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Detecting the effects of forestry on lacustrine sedimentation on the West Coast of Vancouver Island,… Arnaud, Emmanuelle 1997

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DETECTING THE EFFECTS OF FORESTRY ON LACUSTRINE SEDIMENTATION ON THE WEST COAST OF VANCOUVER ISLAND, BRITISH COLUMBIA by EMMANUELLE ARNAUD B.A. (Combined Honours), McMaster University, 1995 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Geography) We accept this thesis as conforming to the requiredjStandard THE UNIVERSITY OF BRITISH COLUMBIA October 1997 © Emmanuelle Arnaud, 1997 In, presenting, this thesis in partial fulfilment of the requirements for an > advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly! purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. ; ' • . .-'.-Department of The University of British Columbia Vancouver, Canada Date! f; 199^ DE-6 (2/88) Abstract Enhanced sediment yield associated with forestry activity is well documented. While some studies have focused on assessing the increase in sediment concentrations of streams, the extent to which sediment is transmitted down valley to storage areas such as lakes remains to be established. There are also unanswered questions about long-term trends in sediment yield. It has been suggested that the study of lake sediments may provide a means to monitor the effects of forestry-related activities. However, a better understanding of the connection between catchment disturbance and lake sedimentation is required to assess the suitability of this approach. To explore these questions, lacustrine sedimentary records from three logged basins and one unlogged basin on the west coast of Vancouver Island, British Columbia were analyzed for physical and chemical properties. Core correlations were based on x-radiography and trends in organic content and magnetic susceptibility. Chronological control provided by 210Pb and 137Cs activity demonstrated that 10-30 cm cores record 100-150 years of sediment deposition and allowed the calculation of sediment accumulation rates. Historical information about both natural and human disturbance in the study areas was compared with changes in sediment characteristics and sedimentation rates. Trends in sediment yield and indicator properties associated with disturbance were thereby identified. The results indicate that increases in sediment yield coincide with forestry-related disturbances, natural disturbances such as rainstorm events, and other human activities such as mining. The identification of the sedimentary signature of forestry-related activity is confounded in one of the logged basins by other catchment disturbances. Depositional events identified on the basis of x-ray stratigraphy and sediment properties also coincide with historically documented instances of localized catchment events such as a landslide or forestry-related mass movement in ii gullies. Of all the sediment properties, changes in the relative proportions of organic and inorganic sediment fractions are most sensitive to upstream catchment conditions as evident from the correspondence between the general change in sediment composition and disturbance history. Methodologically, the results of the study demonstrated that the lake sediment approach may be successful in monitoring the effects of forestry-related activities, although this largely depends on the precision of chronological control, a rigorous sub-sampling strategy and the use of multiple cores. Limitations of the sediment chronology were investigated and show that underestimates of sediment yield may result from assumptions made in the modelling of chronological data. Not all lakes may be suited to this technique due to the resolution required and given that other disturbances occurring in the catchment may obscure inference from the sediment record. in Table of contents Abstract ii Table of Contents iv List of Tables ix List of Figures xi Acknowledgements xv CHAPTER ONE INTRODUCTION 1.1. PURPOSE OF T H E STUDY 1 1.2. RATIONALE OF T H E STUDY 2 1.3. OPERATIONAL OBJECTIVES 6 1.4. D E S I G N OF T H E STUDY 7 1.5. THESIS OVERVIEW 11 CHAPTER TWO LAKE SEDIMENT STUDIES AND THE EFFECTS OF FORESTRY ACTIVITY ON THE SEDIMENT SYSTEM 2.1. INTRODUCTION 12 2.2. L A K E S AS SEDIMENT TRAPS A N D RECORDERS OF C A T C H M E N T CONDITIONS 12 2.2.1. Sediment Sources 14 2.2.2. Processes of Sediment Transfer 15 2.2.3. Catchment factors 16 2.2.4. In-lake factors 19 2.3. EFFECTS OF FORESTRY ACTIVITY O N T H E SEDIMENT SYSTEM 20 2.3.1. Water Yield 22 2.3.2. Suspended Sediment Yield 24 2.3.3. Effect of Forestry Activity on Lake Sedimentation 26 iv 2.4. DISCUSSION 29 C H A P T E R T H R E E M E T H O D S 3.1. INTRODUCTION 31 3.2 SELECTION OF STUDY SITES 32 3.2.1. Selecting comparable basins 32 3.2.2. Selection of lake basins 33 3.2.3 Topographic and air photo survey 34 3.2.4. Field reconnaissance 34 3.3. CORING OF LAKE SEDIMENT 35 3.4. LABORATORY METHODS 38 3.4.1. Whole core analysis 38 3.4.2. Sub-sampling strategy 38 3.4.3. Bulk physical properties 42 3.4.4. Magnetic properties 43 3.4.5. Determination of autochtonous sediments 44 3.4.6. Sediment geochemistry 45 3.4.7. Particle size analysis 46 3.4.8. Sediment dating 46 3.5. CROSS-CORRELATION ANALYSIS AND SEDIMENT YIELD CALCULATION 48 3.6. BATHYMETRIC SURVEY 49 3.7. TERRESTRIAL MATERIALS 50 3.8. SHORELINE SURVEY 50 C H A P T E R 4: T H E S T U D Y A R E A S 4.1. GENERAL PHYSICAL SETTING 52 4.1.1. Geology 52 4.1.2. Climate and Hydrology 57 4.2. MAGGIE L A K E WATERSHED 59 4.2.3. Geomorphology and Drainage Network 59 4.2.2. Disturbance History 63 v 4.3. TOQUART L A K E WATERSHED 65 4.3.1. Geomorphology and Drainage Network 65 4.3.2. Disturbance History 65 4.4. KITE L A K E WATERSHED 69 4.4.1. Geomorphology and Drainage Network 69 4.4.2. Disturbance History 72 4.5. CLAYOQUOT L A K E WATERSHED 72 4.5.1. Geomorphology and Drainage Network 72 4.5.2. Disturbance history 75 4.6. CHARACTERISTICS OF THE STUDY LAKES 78 4.6.1. Maggie Lake 79 4.6.2. Toquart Lake 82 4.6.3. Kite Lake 82 4.6.4. Clayoquot Lake 87 4.7. CATCHMENT COMPARISON AND SUMMARY 90 CHAPTER 5: THE SEDIMENT RECORD 5.1. INTRODUCTION 93 5.1.1. Description of the Sediment Record 93 5.1.2. Chronological Control 95 5.2. MAGGIE L A K E 101 5.2.1. General Stratigraphy 104 5.2.3. Sediment Properties 104 5.2.3. Sediment Chronology 117 5.2.4. Catchment Sediment Yield 119 5.3. TOQUART L A K E 119 5.3.1. General Stratigraphy 120 5.3.2. Sediment Properties 120 5.3.3. Sediment Chronology 128 vi 5.4. KITE L A K E I 2 8 5.4.1. General Stratigraphy 129 5.4.2. Sediment Properties 129 5.4.3. Sediment Chronology 132 5.4.4. Sediment Accumulation Rates and Sediment Yield 134 5.5. CLAYOQUOTLAKE 136 5.5.1. General Stratigraphy 138 5.5.2. Sediment Properties 138 5.5.3. Sediment Chronology 143 5.5.4. Sediment Accumulation Rates and Sediment Yield 144 5.6. CROSS LAKE COMPARISON 146 5.7. MAGNETIC PROPERTIES OF TERRESTRIAL MATERIALS 149 C H A P T E R 6: T H E S E D I M E N T A R Y S I G N A T U R E O F C A T C H M E N T D I S T U R B A N C E 6.1 INTRODUCTION 154 6.1.1. The Potential Bias of the Sediment Chronology 154 6.1.2. The Interpretation of the Sediment Record 157 6.2. T H E REGIONAL TREND IN SEDIMENTATION 158 6.2.1. The Sediment Record of Clayoquot Lake 158 6.2.2. The Sediment Record of Kite Lake Prior to 1978 161 6.2.3. The Inferred Regional Trend 162 6.3. INTERPRETATION OF THE POST 1978 RECORD OF KITE L A K E 163 6.4. INTERPRETATION OF THE SEDIMENT RECORD OF MAGGIE L A K E 164 6.4.1. The Period 1943-1953 164 6.4.2. The Period of 1953-1961 165 6.4.3. The Period 1961-1979 167 6.4.4. The period 1979-1997 168 6.4.5. Sediment Source 170 6.5. CROSS-LAKE COMPARISON AND DISCUSSION 171 vii 6.6. M E T H O D O L O G I C A L DISCUSSION 172 6.6.1. Ideal Lakes and the Failure of Toquart Lake 172 6.6.2. Coring Density and Spatial Variability 173 6.6.3. Relevant Sediment Properties 175 6.6.4. Sensitivity to Change and the Lake-sediment Approach 176 CHAPTER 7: CONCLUSIONS 178 7.7.1. Summary of Findings 178 7.7.2. Recommendations for Future Work 180 References 183 Appendix A Precipitation data 192 Appendix B X-radiographic images of all cores 195 Appendix C Basic physical and magnetic properties of all cores 210 Appendix D Autochthonous sediment, geochemistry and particle size data 224 Appendix E 137Cs and 210Pb data of master cores 236 Appendix F Trap efficiency data 241 Appendix G Catchment sediment yield data 242 Appendix H Magnetic Properties of terrestrial materials 248 viii LIST OF TABLES Table 2.1. Summary of the nature of the influence of in-lake factors at different time scales. . . 21 Table 3.1. Summary of laboratory techniques outlining number of cores analysed, whether or not the analysis is destructive, the sampling interval and the amount of sediment required for the analysis 40 Table 3.2. Summary of cores processed for the more complex analyses. (M- Maggie Lake, T- Toquart Lake, K- Kite Lake, and C- Clayoquot Lake) 41 Table 3.3. Master cores matched for sampling 41 Table 3.4. Results from replicates of measurement of hygroscopic moisture, organic content and carbonate content 44 Table 4.1. Precipitation pattern from the coast to the headwaters of the Toquart Valley (Ministry of Forests, 1993). Period of record is unknown though the station appears to have been established in the early seventies and is no longer being operated 59 Table 4.2. Summary of catchment characteristics 62 Table 4.3. Frequency of landslides in Clayoquot Valley (Fritz, 1996) 78 Table 4.4. Summary of lake characteristics 91 Table 5.1. Average values (±standard deviation) of sediment properties of Maggie cores and core Ml 8 105 Table 5.2. Dates corresponding to sedimentary zones. See text for selection criteria 118 Table 5.3. Sediment yield for Maggie Lake catchment. Minimum and maximum values are based on 95% versus 88% trap efficiency of the lake 120 Table 5.4. Average values (±standard deviation) of sediment properties of Toquart cores and coreT9 122 Table 5.5. Average values (±standard deviation) of the sediment properties of core K2 132 Table 5.6. Age of the sedimentary zones identified in core K2 134 Table 5.7. Sediment yield for Kite Lake catchment. Minimum and maximum values are based on 84% versus 56% trap efficiency of the lake 136 Table 5.8. Average values (± standard deviation) of sediment properties of all Clayoquot cores and core C3 138 ix Table 5.9. Chronology of the sedimentary zones of Clayoquot cores 143 Table 5.10. Sediment yield for Clayoquot Lake catchment. Minimum and maximum values are based on 84% versus 56% trap efficiency of the lake 144 Table 5.11. Summary of coring data 146 Table 5.12. Average values (±standard deviation) of sediment properties of all cores in each lake 147 Table 5.13. Comparison of sediment yield changes over time in the three watersheds 149 Table 5.14. Types of terrestrial material collected in each lake basin 151 Table 5.15. Average SIRM/Xo ratio of terrestrial materials from each watershed 153 Table 6.1. Comparison of mass sediment accumulation (MSA) in master cores with the average MS A based on the MSA in multiple cores 175 L IST OF FIGURES Figure 2.1. Relation between sediment source and sink 13 Figure 3.1. Coring apparatus 36 Figure 4.1. Location of the study area. Dotted lines refer to watershed boundaries and bold text to study lake names 53 Figure 4.2. Geology of the four study watershed (Muller, 1968;Massey, 1994) 54 Figure 4.3. Surficial materials in the study region: a) Maggie Lake watershed, b)Toquart Lake watershed (hammer for scale) 56 Figure 4.4. Mean monthly temperature and precipitation in the study region. Period of record (yrs): Tofino 48, Ucluelet Kennedy camp 26, Estevan Point 83, Carnation Creek 20, Port Alberni 30.(Clayoquot Sound Scientific Panel, 1995) 58 Figure 4.5. Maggie Lake and its watershed. Note mine waste area in the foreground and general relief 60 Figure 4.6. Forestry activity in the Maggie Lake watershed 61 Figure 4.7. The disturbed eastern shoreline of Maggie Lake, showing evidence of mass movement activity along Gully 1, Gully 2, and Gully 3 from left to right. Bridge crossing Gully 3 for scale 64 Figure 4.8. Toquart Lake with Triple Peak and Cats Ears Peak in the background. Note range of relief and timber harvesting next to lake shoreline 66 Figure 4.9. The Toquart Lake watershed showing location of natural and forestry-related disturbance 67 Figure 4.10. Eastern headwater valley, Toquart Lake watershed. Note bedrock failures in the background 68 Figure 4.11. Colluvial fan on the southeast shore of Toquart Lake's lower basin 70 Figure 4.12. The Kite Lake watershed showing location of natural and forestry-related disturbance 71 Figure 4.13. Disturbance related to forestry activity: a) overview of Kite Lake and timber harvesting of 1992, b) the effect of windthrow on buffer and lake shoreline 73 Figure 4.14. The Clayoquot Lake watershed showing location of landslides (Fritz, 1996) . . . . 74 xi Figure 4.15. Landslide above Clayoquot Lake (October, 1995) 77 Figure 4.16. Maggie Lake: a) bathymetric map showing echo sounder transects and coring locations, b) map showing shoreline features. Fans are not drawn to scale. Majority of shoreline has been logged in the last 20-30 years 80 Figure 4.17. Echo sounder charts from Maggie Lake. See Fig. 4.16 for location of transects. Note different scales of each chart. Evidence of slumping (arrow) at the base of slope can be seen on the C-C transect 81 Figure 4.18. Toquart Lake: a) bathymetric map showing echo sounder transects and coring locations, b) map showing shoreline features. Fans are not drawn to scale 83 Figure 4.19. Echo sounder charts from Toquart Lake. See Fig. 4.18 for location of transects. Note different scales of each chart. Depth at J is >10 m as transect was started at the fish hatchery 84 Figure 4.20. Kite Lake: a) bathymetric map showing echo sounder transects and coring locations, b) map showing shoreline features. Fans are not drawn to scale 85 Figure 4.21. Echo sounder charts from Kite Lake. See Fig. 4.20 for location of transect 86 Figure 4.22. Clayoquot Lake: a) bathymetric map showing echo sounder transects and coring locations, b) map showing shoreline features. Fans are not drawn to scale 88 Figure 4.23. Echo sounder charts from Clayoquot Lake. See Fig. 4.22 for location of transect. Note subaqueous channel 89 Figure 5.1. Profiles of 137Cs activity, with 210Pb derived dates for comparison from the master cores of: a) Maggie Lake, b) Toquart Lake, c) Kite and Clayoquot Lakes. The grey box highlights the 1963 maximum in 137Cs activity, while the arrow points to the onset of the rise in activity corresponding to 1954. Blank intervals were not measured 96 Figure 5.2. X-ray image of Maggie Lake cores showing variations in the general grey tone pattern across the lake (Figure 4.16 for core locations). Arrow points to change from light grey to darker grey tone: a) upper basin, b) lower basin 102 Figure 5.3. Summary diagram of sediment properties of core Ml 8 106 Figure 5.4. Geochemical stratigraphy of core Ml 8. Precision is within 5% for all elements except for calcium which has a precision value of 9%. Lead concentrations fell below detection level 107 Figure 5.5. Downcore and spatial variability of organic content in Maggie Lake cores: a) upper basin, b) lower basin. Note cores are arranged to reflect location in the lake (Fig. 4.16) 109 xii Figure 5.6. Downcore and spatial variability of magnetic susceptibility in Maggie Lake cores (cf. Fig. 5.4): a) upper basin, b) lower basin. Note cores are arranged to reflect location in the lake (Fig. 4.16) 112 Figure 5.7. Summary diagram of sediment properties for core M12. Note SIRM/Xo value in M-C is missing 115 Figure 5.8. Geochemical stratigraphy of core Ml 2. Precision is within 5% for all elements except for one replicate of Na and Si which have precision levels of 15 and 10 % respectively. Lead concentrations fell below detection level 116 Figure 5.9. X-ray image of Toquart Lake cores showing variations in the general grey tone pattern across the lake. See Figure 4.18 for core locations 121 Figure 5.10. Summary diagram of sediment properties of core T9. Note Zone T-A is not observed in this core. The top three values of bulk density are most likely an artifact of the different sampling technique used in this part of the core 124 Figure 5.11. Geochemical stratigraphy of core T9. Precision is within 5% for all elements except for calcium which has a precision value of 5.1 and 5.4%. Cadmium and lead concentrations fell below detection levels for most of the profile 125 Figure 5.12. Downcore and spatial variability of organic content in Toquart Lake cores: Note cores are arranged to reflect location in the lake (Fig. 4.18) 126 Figure 5.13. Downcore and spatial variability of magnetic susceptibility in Toquart Lake cores. Note cores are arranged to reflect location in the lake (Fig. 4.18) 127 Figure 5.14. X-ray image of core K2. Note the sandy layer and the graded nature of the zone boundaries 130 Figure 5.15. Downcore and spatial variability of organic content and magnetic susceptibility in Kite Lake cores showing lack of cross-core correlation. Cores are arranged to reflect location in the lake (Fig. 4.20). Note the cyclical nature of the organic profile of K2 131 Figure 5.16. Summary diagram of sediment properties of core K2 133 Figure 5.17. Temporal variability in sediment accumulation rates in core K2 based on lead-210 dates. Shading highlights changes in rates 135 Figure 5.18. X-ray image of core C3. Note the marker horizon at the base of Zone C-A . . . . 137 Figure 5.19. Summary diagram of sediment properties of core C3 140 xiii Figure 5.20. Geochemical stratigraphy of core C3. Precision is within 5% for all elements except for sodium and potassium which have precision levels of 5-6%. The poor precision level in the measurement of Cd is offset by its close correlation with other elements . . 141 Figure 5.21. Downcore and spatial variability of organic content and magnetic susceptibility in Clayoquot Lake cores. Cores are arranged to reflect location in the lake (Fig. 4.22) . 142 Figure 5.22. Temporal variability in sediment accumulation rates in core CI based on lead-210 dates. Shading highlights peaks in accumulation rate 145 Figure 5.23. Location of the terrestrial surface material samples from the four study watersheds 150 xiv ACKNOWLEDGEMENTS I recognize that this study was carried out on traditional Nuu-Chah-Nulth lands and trust that the results will be of value to the people for their stewardship of the land. I would first like to thank my supervisory committee: June Ryder, my supervisor, for her guidance and helpful discussions throughout the duration of this project; Michael Church for technical advice, discussions, and his patience for putting up with my endless stream of questions; and Hans Schreier for advice and encouragement. Kurt Grimm's enthusiasm and brainstorming sessions were also appreciated. Carolyn Eyles motivated much of my decision to undertake my Masters degree. The project was funded by a Forest Renewal British Columbia grant to Michael Church and by an NSERC scholarship to Emmanuelle Arnaud. This financial support is greatly appreciated. Rick Nordin from the Ministry of Environment, Land and Parks generously lent his K-B corer for the retrieval of the sediment cores. The Clayoquot Biosphere Project is thanked for the use of their field station in the Clayoquot valley. Graham Shivers is thanked for his enthusiasm in the field, and for building Gilda. Field assistance from Gord Drewitt and Mike Church is also acknowledged. Many individuals are thanked for their technical assistance with the analyses of lake sediments: Spencer Dearing of the Radiology Department at the UBC hospital for x-rays of the cores; Randy Enkin at the Pacific Geoscience Centre in Sidney for his assistance with the magnetic analyses; Ahn-Toan Tran in the Soil Science Laboratory at UBC for conducting geochemical analyses (courtesy of Hans Schreier); Jack Cornett and Janice Lardner of MYCORE Scientific for lead-210 analyses; Dr. Joe Desloges of the Department of Geography, and Dr. Sandu Sonoc of the Department of Chemical Engineering at the University of Toronto for supervising and carrying out the caesium analyses; Maureen Soon of the Department of Earth and Ocean Sciences, UBC for teaching me the 210Pb provedure and for introducing me to HF; Dr. Humphrey of the Bioscience Electron Microscopy Facility for the use of photography equipment in the Bioscience Department, UBC; Doug Poison and Ray Rodway from the Earth and Ocean Sciences Department, UBC, for helping me with the cutting of the frozen cores (courtesy of Kurt Grimm) and Abid Sivic from the geography Department, UBC, for making the frozen sediment sampler and the sediment trays. All lab analyses were made possible through the enthusiastic commitment and conscientious work of Christy Gold. The following individuals contributed their time to this project through discussions, contacts and reports: John Crusius from the Department of Earth and Ocean Sciences, UBC, Brian Cumming and Kate Laird, from Queen's University; Shelly Higman from MacMillan Bloedel Ltd., Woodlands Division; Shawn McLennan and Flip Wilson from MacMillan Bloedel, Ltd., Kennedy Lake Division; Terry Rollerson, Chief of Research, Vancouver Forest Region, Ministry of Forests; Bruce Thomson, Regional Geomorphologist, Ministry of the Environment; Rob Hudson from the Vancouver Forest Region; Rhonda Morris from the Ministry of Forests, Port Alberni District Office; Peter Fritz; Audrey Pearson and Karen Halwas. xv I also thank Josie Cleland of the Clayoquot Biosphere Project for her assistance and Mike Greig, of EnFor Consultants Ltd, who was particularly helpful with the Toquart watershed history. Air photos for the watersheds of Maggie and Clayoquot lakes were made available by MacMillan Bloedel Ltd. (Woodlands Services Division). Revisions by June Ryder, Mike Church, and Gord Drewitt greatly improved this manuscript. Vincent Kujala's ongoing help with computer glitches and Bobby Levac's rescue of my hard drive are greatly appreciated. Boyd Benson, Trina Bester, Gord Drewitt, Grant Duckworth, Martin Evans, Wendy Hales, Nicky Hicks, Kristen Johnston, Yvonne Martin, John McNern, Brian Menounos, Juliet Rowson, Judy Tutchener, Kamala Todd, Bruce Willems-Braun and Stephanie Wood are all thanked for making my stay at UBC a memorable one. I also thank my family for their love and support. Lastly, four people were particularly instrumental in the successful completion of this thesis: Martin Evans and Brian Menounos for numerous discussions and technical advice on the study of lake sediments, Christy Gold for making lab work so entertaining and Marie Graf, for her unfailing encouragement. -Thank you xvi Chapter 1 Introduction 1 l . l . PURPOSE OF T H E STUDY The purpose of this study is to gain a better understanding of the relation between changes in catchment conditions associated with forestry activity and downstream lacustrine sedimentation. Changes in catchment conditions following timber harvesting are easily identifiable in the British Columbia landscape: accelerated surface erosion and hillslope instability associated with roads, accelerated surface erosion and hillslope instability associated with the removal of vegetation along gullies, and windthrow of trees left standing at the edges of clearcuts. Sediment transfer from sediment source areas to downstream storage points, such as lakes, is influenced by natural and local factors. Hydrology and topography, affect sediment transport processes, while natural disturbances, which may coincide with land-use changes can confound the assessment of the human-induced change. Lake sediments in the end bear the imprint of both the initial change in catchment conditions and the subsequent transformation of that change as the sediment moves from its original source to the lake. The purpose of the study is therefore two fold: the sediment record is examined knowing the disturbance history 1) to determine how lake sediments and sedimentation rates have been affected by forestry activity and 2) to assess how natural and local factors have affected how these changes are recorded in the sediment record. An important aspect of this study is to determine the applicability and feasibility of lake sediment studies to monitor the effects of forestry activity on watersheds. The attractiveness of this approach is that it addresses the issue of surface erosion at the basin scale rather than the site-specific scale, thereby taking into consideration integrated effects which are often difficult to predict. However, are lakes and lake sediments sensitive to upstream changes? What technical 2 expertise and equipment does the approach require? Can changes be resolved at a short time scale of 5-10 years? The purpose of this study includes addressing these methodological considerations. 1.2. RATIONALE OF THE STUDY The study of human impact on sedimentation has been explored within the framework of studies of lacustrine sedimentation for environmental reconstruction and erosion/sediment yield. Environmental reconstructions from lake sediments have focused on characterizing changes in vegetation (e.g. Kremenetsky, 1995), climate (Last and Schweyen, 1985), geomorphic activity (Souch, 1994), and land-use history (Dearing et al, 1981). In contrast, studies of erosion and sediment yield have focused on quantifying the increase in sediment influx to streams and lakes by looking at contemporary processes and stratigraphic records (Bathurst, 1994). Each of these strategies covers different time scales. The analysis of lake sediments has proved fruitful in attempts to reconstruct the environment of the surrounding watershed. Analyses of sedimentary structures, sediment composition, grain size distribution, sediment geochemistry, and fossils have been used to infer the nature of depositional environments. The sediment record has been dated using known chronological markers, such as volcanic deposits, or using dating techniques such as carbon-14, lead-210, caesium-13 7, and thermoluminescence. Temporal variations in sediment properties and accumulation rates can thus be determined. Successive changes in sediment characteristics and accumulation rates represent sequential changes in depositional conditions, allowing past vegetation, climate, geomorphic acitivity and glacial history to be reconstructed over 103 -10s years. 3 Studies of surface erosion and sediment yield evolved out of an interest in the impact of agriculture on sedimentation. This field of research traditionally used hillslope plot studies and long-term monitoring of suspended sediment concentrations in streams to address the issue of accelerated surface erosion. It is a well-established discipline as evident from the numerous special volumes on this subject (e.g. Davies and Pearce, 1981; Hadley and Walling, 1984; Boardmanera/., 1990; Thornes, 1990; Bathurst, 1994, Walling and Webb, 1996). Different types of changes in land-use and the resulting effects on the sediment system have been studied with primary focus on the impact of intensified agriculture, overgrazing and mining activity, and the resulting environmental quality of rivers over the last century (Bathurst, 1994, and Foster et al, 1995). Such process-based studies however require long-term sedimentation records to contextualize the short-term sediment yield they document (Bathurst, 1994). In this respect, Oldfield (1977) recognized that lake-based sediment yield studies provide long-term records that span the periods both before and after disturbance, without the expensive maintenance of long-term stream gauging stations. Subsequently, a number of studies focused on determining sediment yield data from lacustrine sediment records and on establishing a relation between sediment source within the catchment and sediment input into the lake. Many have shown that changes in sediment yield as a result of changing patterns of land-use can be detected in lakes (e.g. Davis, 1976; Dearing et al, 1981; O'Hara et al, 1993). Several issues were identified through this work: the influence of storage in affecting sediment delivery to lakes and the time scale of sediment movement, and the importance of episodic events. A critical review of work done in environmental reconstruction from lake sediments and of studies of erosion/sediment yield reveals several areas requiring further research. The majority of research into human impact on the lacustrine sediment system from the perspective of environmental reconstruction has been carried out at time scales of several hundreds to thousands of years. Moreover, many lake-based palaeoecological studies focus on reconstructing changes in distribution and type of vegetation, making only scant remarks concerning the influence of vegetation in regulating sediment production and lacustrine sedimentation rates. Erosion/sediment yield studies have focused on the effect of vegetation removal on sediment production and lake sedimentation on much shorter time scales, but much of this research has been carried out in areas where the physical environment and land-use history are quite different from coastal British Columbia. In general, questions remain about the relative importance of the human impact in the context of long-term trends and the significance of temporary upstream storage of sediments. The West coast of Vancouver Island was chosen as a suitable location for this study for a number of reasons. As mentioned previously, very few studies have been carried out in this type of physical environment. Vancouver Island has been the focus of international attention as an area experiencing the impact of clear-cut logging. The area has been relatively unaffected by other kinds of human activities, allowing the current study to focus on forestry as a source of change in catchment conditions. The current study will contribute to the specific understanding of the local sedimentation regime and to a more general understanding of the ecosystem's response to recent human-induced change. An important aspect of sustainable ecosystem management is monitoring, which is defined as "repeated observation, through time, of selected objects and values in the ecosystem in order to 5 determine the state of the system" (Clayoquot Sound Scientific Panel, 1995, p. 189). Monitoring contributes to sustainable management of forest resources in three ways: First, it ensures that current practices comply with forest practices standards; second, it helps determine whether the recommendations adopted for the management of a watershed are appropriate; and third, it provides a basis for understanding the mechanism of human-induced and natural changes in ecosystems. The current study not only contributes to this third goal but has the potential to be developed as a way to fulfil the first and second goals by providing a means to assess the effect of forestry activity. The rationale for the methodological aspect of this project stems from the need to know whether lake-based sediment yield studies are appropriate for monitoring the effects of forestry activities in this particular physiographic region. Local environmental factors such as high precipitation, steep terrain and glacial and seismic history, which differ from the few other sites where similar work has been carried out, may complicate the identification of the signature of forestry activity in lake sediments. Several aspects of the lake sediment approach also need to be refined before its widespread use can be implemented. More work is required to develop criteria for the selection of lakes which are most likely to be sensitive recorders of catchment conditions. While multiple coring studies are more time-consuming and costly, they allow a much more accurate representation of lake-wide conditions than single core studies. What is the optimum coring density that is required to assess spatial variability in sediment deposition? The short time scale of this type of study (on the order of 100 years) stands in contrast to those carried out for environmental reconstruction over thousands of years. The short sedimentary record available, requiring high resolution analysis, also needs to be considered when developing laboratory 6 techniques. Likewise, the sediment properties most likely to record changes in catchment conditions associated with forestry activity need to be identified. These methodological considerations will be addressed in the overall consideration of the suitability of this approach. 1.3. OPERATIONAL OBJECTIVES Based on previous studies which documented changes in lake sediments related to forest clearance (e.g. Davis, 1976; Laval etal, 1991), a downstream sedimentation response was expected in the form of an increase in clastic sediment accumulation and a change in sediment composition. However, the relation between land-use change and lacustrine sedimentation is expected to be complex due to secondary responses within the system, the region's physical configuration, and the coupling between sediment mobilization on hillslopes and downstream lacustrine sedimentation. The following research questions will be addressed in order to gain a better understanding of the relation between catchment changes and lake sedimentation. • What sediment properties are indicative of catchment disturbance? • Does timber harvesting and related forestry activity such as the construction of logging roads cause an increase in sedimentation in storage areas such as lakes? • If so, how have sediment accumulation rates changed? • What is the spatial nature of the response? • Are lag effects expressed in the sediment record? • Can the increase in sedimentation be attributed with relative confidence to increase surface erosion from logging activity or are other sources or indirect effects of logging confounding the record? Is this approach an appropriate method to monitor the effects of forestry activity? 7 These questions are the critical issues: lake sensitivity to change, sediment storage, transfer and delivery between source and sink, lag effects, and identification of sediment sources. 1.4. DESIGN OF T H E STUDY It is important to be able to distinguish variability in sediment properties and sedimentation rates associated with local changes (possibly a consequence of land-use) from those associated with regional environmental change. Thus, the classic paired-catchment approach, widely used in hydrological studies, was adopted for the current study to provide some control over varying external factors (i.e. climate, topography and earthquakes). One unlogged lake basin and three lake basins with different harvesting histories were selected and compared with historical records of natural and human disturbance. Differences among the four sedimentary records can then be linked to differences in local disturbances, thereby providing an understanding of the effect of environmental change in the catchment on lake sedimentation. The comparative approach requires that the drainage basins be relatively similar, although this outwardly appears quite difficult since no two catchments are ever alike. It is important however to maximize the similarity of paired catchments and to establish their degree of similarity in order to eventually explain the similarities and differences found in the sediment record. To examine the response of the sediment system to disturbance, changes in sediment properties and sedimentation rates were assessed in the four lacustrine sediment records. Sediments obtained from lake-bottom cores were analysed to determine successive changes in 8 organic content, moisture, bulk density, particle size, magnetic properties, and sediment geochemistry. Analyses were also carried out to determine the portion of the sediment which is derived from in-lake processes. Pollen analyses were not carried out since historical records of the onset of forest clearance are available for all three logged basins. Results from each of these analyses were then interpreted and compared with the known disturbance history of each catchment. Interpretation of the sediment record is based on the following general principles. Changes in organic content can be indicative of changes in the mobilization of organic matter from the contributing catchment and of in-lake processes and depositional conditions; they may also be related to changes in the input of inorganic sediment. Moisture and bulk density are often related to organic content. Changes in particle size were interpreted as being a function of a change in sediment source and/or a change in sediment transfer processes. Magnetic susceptibility was used as a measure of the concentration of magnetite grains, a common mineral in weathered materials (Thompson and Oldfield, 1986). Magnetic susceptibility of topsoils is often enhanced due to the development of magnetite and maghemite (Oldfield etal, 1979). Increases in the magnetic susceptibility of lake sediments have been linked to periods of increased surface erosion (e.g. Thompson etal., 1975; Dearing etal, 1981). Fluctuations in magnetic susceptibility are indicative of changes in the inorganic or clastic fraction of the sediment. Fluctuations in geochemical element concentrations were examined to assess changing geochemical conditions both within the lake and within the soils of the contributing watershed. For example, a decrease in sodium and potassium may be explained by either increased stability of soils allowing leaching of these two elements to occur before the soil is eroded and incorporated 9 into lake sediments (Mackereth, 1966), or increase biogenic silica or carbonate influx diluting the otherwise constant minerogenic composition of the sediment (Engstrom and Wright, 1984). Synchronous levels of sediments in different cores were identified using several sediment properties in order to determine spatial variability in sediment deposition across each lake (Dearing, 1986). Magnetic susceptibility and x-radiography were used for the definition of lake-wide zones (Bloemendal etal., 1979; Axelsson, 1983). In addition to these two parameters, organic content proved to be useful in cross-core correlation. Based on correlation of synchronous levels, properties of master cores derived from the more complex analyses were extrapolated to the rest of the cores across the lake, allowing calculation of clastic sediment yield for each basin. Lastly, sedimentary chronologies of the different lakes were correlated and regionally significant markers identified, allowing comparison between lakes, an essential component of the paired catchment approach. Lead-210 (210Pb) and caesium-137 (I37Cs) isotopes were used to define the sedimentary chronology. Lead-210 is useful for dating sediments deposited in the past 150 years while 137Cs allows the dating of sediments from 1954 onwards (Wise, 1980). These have been successfully used elsewhere for the radiometric dating of recent lake sediments (e.g. Pennington et al. 1973; Dearing et al., 1981, Davison etal., 1985). Other techniques are either less well developed and therefore less accurate, or are applicable for very specific environments and materials (Lowe and Walker, 1984). Lead-210 is a natural isotope and a member of the 2 3 8 U decay series with a half life of 22 years (Olsson, 1986). The 210Pb activity found in lake sediments is made up of two components. The supported component is derived from the decay of uranium and other earlier members of the series found in minerogenic lake sediments (Olsson, 1986). The method assumes that this 10 component is always in radioactive equilibrium with its parent nuclides, leading to a constant supply of supported 210Pb at all depths (Wise, 1980). The unsupported component of downcore 210Pb activity is derived from the decay of 222Rn in the atmosphere. Once it is incorporated into the sediment, it will decay and eventually disappear completely after 150 years. A sedimentary chronology is inferred from the decay constant of 210Pb and the observed downcore decrease in unsupported 210Pb activity. Background levels which correspond to the supported component of total 210Pb activity are first determined by analyzing the deepest sections of cores believed to be older than 150 years. This component is subtracted from the total 210Pb activity to establish a downcore profile of the unsupported activity. Cs-137 is a by-product of atomic testing, and is detectable in sediments deposited during and after 1954 (Wise, 1980). The amount of 137Cs deposited is dependent upon latitude and annual rainfall (Ritchie and McHenry, 1990). Peak fallout periods in 1959 and 1963 have been identified in sediments at other sites in southern British Columbia (Ashley and Moritz, 1979; Mathewes and D'Auria, 1982, Clague et al, 1994; Williams and Hamilton, 1995). Caesium concentration is measured downcore and a profile generated. Three dates are inferred: 1954, when the 137Cs concentration begins to rise; 1959, at the first substantial peak; and 1963, at the highest peak in the profile (Ritchie and McHenry, 1990). In lake sediment studies focused on the history of catchment surface erosion and sediment yield, the various sources of lake sediments (weathered bedrock, surface erosion, and channel erosion in contributing creeks and rivers) need to be distinguished. Issues of sediment source can be resolved by comparing the magnetic properties of terrestrial materials to those of lake sediments (Oldfield etal., 1979; Dearing etal., 1981; and Thompson and Oldfield, 1986). The ratio of saturated isothermal remanent magnetization to magnetic susceptibility (SIRM/Xo) is a funtion of the size of magnetic grains. As different materials have different SIRM/Xo ratios, shifts in the magnitude of that ratio are interpreted as changes in sediment source. A comparison of the magnetic properties of lake and terrestrial sediments and bedrock specimens was undertaken to address the issue of sediment source in the current study. Other methods of sediment tracing, including x-ray diffraction and scanning electron microscopy, were not explored. 1.5. THESIS OVERVIEW The following chapter reviews our current knowledge of the links between sediment sources and lakes, as well as the effects of forestry activities on the sediment system. The methods adopted in order to explore the questions raised above are described in detail in chapter 3. A description of the study areas ensues, including both the physiographic setting of each lake basin and the history of natural and human disturbance. The result of all analyses are presented in chapter 5 and discussed in chapter 6 in the context of the original objectives of the study. Lastly, chapter 7 provides a summary of the findings and makes recommendations for future work. 12 Chapter 2 Lake sediment studies and the effects of forestry activity on the sediment system 2.1. INTRODUCTION The following literature review is organized in two sections. The first considers lakes as sediment traps and recorders of catchment conditions. The sensitivity of lacustrine sedimentation to human-induced changes in catchment conditions is demonstrated by reviewing the linkages between sediment sources and sinks and the processes which influence the sediment cascade. Components of the system most relevant to the time scale under study are highlighted. The conceptual framework of the current research is thus established. The second section reviews current knowledge about the effects of forestry activity on the sediment system, with specific emphasis on water yield, suspended sediment concentrations and lacustrine sedimentation. The limits of our understanding concerning the nature of forestry-related impacts on lacustrine sediment regimes are considered, and ways in which the present project may contribute to this field of study are discussed. 2.2. L A K E S AS SEDIMENT TRAPS AND RECORDERS OF CATCHMENT CONDITIONS Lake sediments originate from their surrounding basins and as such bear the imprint of catchment conditions. Sediments from various sources are transported by fluvial and mass movement processes to downstream depositional environments such as lakes. Catchment and in-lake factors influence the transfer of sediments between source and sink, affecting both the delivery of sediments to lakes and the nature of lacustrine sedimentation (Fig. 2.1). As a result, 13 Source material Surface erosion Mass movement processes Allogenic sediments Climate Vegetation Hydrology Geology and topography Sediment routing and storage on hillslopes Human activity Natural disturbances CATCHMENT FACTORS ;, Storage as fluvial sediments Fluvial Processes Terrestrial In Lake Allogenic sediments In-lake Processes • ( Autogenic sediments Lake capacity Shape factor Temperature Density currents Particle fall velocity Water chemistry Sediment remobilization Outflow configuration Inflow characteristics Sediment characteristics Effective depth IN-LAKE FACTORS Figure 2.1: Relat ion between sediment source and sink. 14 lake sediment studies provide "integrated insight into ecosystem variation on all time scales" (Oldfield, 1977, p. 462). The major components of the sediment cascade system are reviewed below. An understanding of the various sources, transfer mechanisms and catchment and in-lake factors is essential in the study of sediment yield and lacustrine sediment records. 2.2.1. Sediment Sources Lake sediments are divided into two main categories based on their origin: allogenic sediment, derived from outside the lake, and autogenic sediment derived from biochemical processes within the lake. These can be further divided into their organic and inorganic components. The allogenic fraction can consist of detrital minerals from various sources, detrital organic material (e.g. needles, wood chips), allogenic diatoms, phytoliths and soil organic matter, while the autogenic fraction can consist of organic matter produced by organisms and algae, diatom frustules or biogenic silica, secondary minerals and adsorbed ions (Likens and Moeller, 1985). Hakanson and Jansson (1983) defined the autogenic component as derived solely from the physical and chemical processes within lake-bottom sediments and an endogenic component derived from precipitates and flocculates in the water column. Though conceptually useful, this distinction is hard to make in practice. Thus, the broader definition of autogenic will be used for this study. There are several catchment sediment sources to be considered: top soil, colluvium, glacial sediments, local bedrock, aeolian particles, and channel bank sediments. Through an analysis of sediment yield in several alpine catchments, Owens and Slaymaker (1993) distinguished between inputs derived from aeolian dust, diatoms, organic matter, lake shore erosion, colluvial and fluvial origins. Using scanning electron microscopy and x-ray diffraction analyses, Souch (1994) was 15 able to distinguish between sediments derived from glacial material and those derived from colluvial deposits. Dearing et al. (1981) used magnetic susceptibility to separate sediments derived from channel erosion from those derived from top soil erosion. The first study differentiated between major sediment sources, while the last two identified different allogenic mineral sources. Despite the geomorphologist's primary interest in clastic sediments, it is important to have an understanding of the organic component of lake sediments. Organic content may give an indication of influx of organic matter related to changes in vegetation cover on nearby slopes, mobilization and transfer of organic debris, and changes in the autogenic production of organic sediment (Pennington and Lishman, 1971; Pennington, 1981). This seems particularly significant in the current study, where mobilization of organic debris during forestry activity is likely, and event layers in the sedimentary record vary in composition between predominantly sandy and predominantly organic deposits. 2.2.2. Processes of Sediment Transfer Under natural conditions, surface erosion and fluvial and mass movement processes are responsible for the transfer of sediments from the hillslope to the basin outlet. Surface erosion processes include, slope wash, gully erosion and tree throw. The latter is defined as the downslope movement of organic and inorganic material by fallen trees (Roberts, 1984). Tree throw is a significant process under forested conditions prevalent in coastal British Columbia, since surface erosion from surface runoff is limited (Chamberlain, 1982). Mass movement processes which predominate in the study basins include surficial material landslides and bedrock failures. Different types of landslides which commonly occur in the 16 Vancouver Island Mountains (debris slides, debris flows) are distinguished by material type, rate of movement and moisture content (Swanston and Howes, 1994). Debris flows are the rapid downward flow of saturated organic and inorganic materials. Also known as debris avalanches, debris slides are low in moisture content or only near-saturated and involve the sliding and tumbling of loose material along a failure plane (Swanston and Howes, 1994). There are two types of bedrock failures. Rock slides involve the downward movement of bedrock along a sliding plane where as rock falls involve the downward movement of bedrock by free falling, rolling or bounding (Swanston and Howes, 1994). Bedrock failure is only significant on the steepest terrain of the study basins. In terms of fluvial processes, fine sediment is carried in suspension by streams while coarser sediment moves through rolling, sliding and saltation. Channel bank sediments or those within the streambed can be mobilized as a result of increased discharge, changes in flow patterns following disturbance of bed morphology or failure of a large woody debris (LWD) jam. The latter mechanism is particularly significant in small streams of coastal Vancouver Island (Church, 1995). 2.2.3. Catchment factors Within each of the study basins, various factors will determine the nature of the sediment yield response to changes in land-use patterns. In the broadest sense, environmental variables affecting sediment yield from an area are climate, geology and topography, human activity and storage (Fig. 2.1). Climate drives variability at the synoptic, seasonal, and annual scales as storms affect runoff rates and sediment mobilization, thus having a considerable effect on sediment yield and the sediment record (Dearing and Foster, 1986). In small basins, storm events cause mobilization of sediments, producing discrete stratigraphic horizons which can be factored into yield estimates (e.g. Desloges and Gilbert, 1994). Local variability in storm events and rainfall intensity are particularly significant on the west coast of Vancouver Island (Clayoquot Sound Scientific Panel, 1995). Vegetation cover affects sediment yield and lacustrine sedimentation by trapping sediment upstream of the lake as well as protecting against surface and shoreline erosion. Vegetation also affects the water balance of an area by intercepting precipitation and reducing soil moisture content through evapotranspiration. As a result, runoff generation may be delayed. Vegetation is considered a steady factor except for the dynamic changes effected by forestry activity. By virtue of the location of the study area where vegetation is abundant and grows rapidly, this catchment factor, the degree to which it is altered by forestry activity and the rate of recovery will be critical in determining the downstream lacustrine response. Hydrology is controlled by climate and influenced by the nature of the drainage network, surface materials and vegetation cover of each basin. Subsurface hydrological processes during storms influence slope stability, and rates of weathering. Variability of stream discharge influences sediment transport rates, and depositional and erosional processes within the fluvial system. The geology of the study watersheds will determine the kinds of material available to the sediment system. Thus, basins dominated by thin surficial materials and extensive resistant bedrock outcrops have low sediment yields, while those with a more extensive cover of glacial sediments or easily weathered bedrock have greater sediment yields. Geology is considered a steady external condition because, while different bedrock types may lead to different erosion rates, individual rates are not expected to change over the period of interest. 18 Slope gradient and relief strongly influence rates of transfer of sediments within the study basins. Like geology, these are unlikely to change. In the event of a low frequency high magnitude event such as a landslide or debris flow, the connectivity between the hillslope where the event occurred, the fluvial system and the lake is key in determining its impact on downstream lacustrine sedimentation. This kind of change is not likely to be significant in terms of the overall topography of basins but will most likely affect the sediment cascade. Perturbations which can affect the sediment system are fire, forest condition, and earthquakes. Fire, natural or human-induced, affects vegetation cover, exposing and disturbing the soil. Fire has not been a significant factor affecting the sediment cascade of the study basins within the time frame covered by the current study. Trees can also be affected by disease which again may alter soil properties, erosion potential and stability. Mathews (1979) documented occurrences of landslides throughout the study region associated with the 1946 Vancouver Island earthquake which was centred on the eastern coast of central Vancouver Island. Human activity can affect the sediment system at all spatial and temporal scales. The nature of the response of the sediment system of the study basins depends on the type of land-use or disturbance, the extent of the disturbance, the duration of the activity causing the change, and the intensity of the impact. While land-use may seem to impact only one aspect of the watershed ecosystem, the response is often complex due to the inter-relations between various physical and biological systems. The extent of the human activity is an important factor in determining its impact on the overall watershed. For example, some studies suggest a minimum of 25% of the watershed has to be clear-cut in order to affect annual water yield (Hornbeck et al, 1993). The location of the human activity also needs to be considered. For example, surface erosion may not be recorded downstream if the upstream source of sediment is not coupled with fluvial transfer 19 mechanisms. An important 'filter' within the catchment is sediment routing and upstream storage of sediments. Periods of accelerated erosion can be followed by delayed or prolonged periods of increased sediment yield because much of the sediment remains in storage on the hillslope or along the river only to be released during subsequent periods of erosion (e.g. Meade, 1982; Trimble, 1990). In the current study area where moderately steep terrain and high precipitation is common, delays in the sediment delivery of mobilized sediments are unlikely. Landslide event which can produce much sediment often occur during rainstorm events. While coarse sediments may be stored upstream, fine sediments are most likely to be entrained and delivered downstream relatively quickly following disturbance. Prolonged increases in sediment yield may occur from erosion of the landslide deposit or from remobilization of sediments which were deposited in the streambed. Streambed gravels are turned over and washed in most winters so that the latter factor would most likely only prolong the change in sediment yield by one or two years (pers. comm. Church, 1997). The degree to which fine sediments from natural or forestry-related landslides are coupled with the drainage system and the occurrence of upstream storage need to be assessed when interpreting the sediment yield record of each lake. 2.2.4. In-lake factors Once the sediment reaches the lake, sedimentation processes and reservoir configuration influence outflow losses, and determine the lake's ability to trap sediments. Heinemann (1984) presented a comprehensive model which summarizes the factors controlling trap efficiency. Sediment influx characteristics (including volume, particle size and chemical properties), and discharge characteristics determine both the retention time and the nature of the ensuing 20 interaction with the lake water. In the lake, water characteristics, lake capacity, and lake shape affect the process of sedimentation and retention time. The model uses a cascade system approach and makes a useful distinction between factors related to the incoming water and sediment, those associated with sedimentation within the lake and those associated with outflow losses. There are several elements that Heinemann (1984) did not specifically identify. Evaporation and seepage are not considered as outflow losses. These may be of importance since they most likely constitute sediment-free losses. The reservoir water chemistry and the role of sediment compaction in the loss of capacity is also not explicitly identified. The latter is unlikely to be significant over the time scale of the current study. The relative importance of parameters controlling trap efficiency and sedimentation varies over different time scales and can be described as having a variable or steady influence on lacustrine sedimentation (Table 2.1). In summary, the important elements of the sediment cascade system which affect sediment yield and lake sedimentation are sources, transporting processes, catchment characteristics and in-lake factors. Variability in these elements has to be considered when trying to detect the onset of forestry activity and accelerated erosion in lake sediments. 2.3. EFFECTS OF FORESTRY ACTIVITY ON T H E SEDIMENT SYSTEM Having established the connection between sediment sources and the lake as a sediment trap, studies of the effects of forestry activity are reviewed to demonstrate which components of the sediment system are affected by timber harvesting operations. Hydrological effects of forestry activity have been monitored in many paired catchments as well as in single watersheds with pre-and /wsMreatment monitoring of water yields and suspended sediment concentrations 21 Table 2.1: Summary of the nature of the influence of in-lake factors at different time scales. In-lake factor Event Scale (1 hour-1 week) Seasonal Scale (1 month-1 yr) Intermediate Scale (103- 106yrs) Large Scale (103- 106yrs) inflow characteristics variable variable variable variable sediment characteristics variable variable variable variable particle fall velocity variable variable steady steady outflow losses variable variable variable variable effective depth variable variable steady steady lake shape steady steady steady variable lake capacity steady variable variable variable sediment compaction steady steady variable variable -inflow characteristics include magnitude and duration of peak and base flow, water chemistry, density and temperature, -particle fall velocity is a function of water temperature, sediment size, currents, -effective depth is a function of chemical and thermal stratification. -reservoir capacity is a function of water levels as well as sediment accumulation and compaction. It is variable at the seasonal scale because of changing water levels. Both changing water levels and loss in capacity due to the accumulation of sediments (counteracted by compaction) become factors at intermediate and large scales. 22 (see Whitehead and Robinson, 1993 and Bosch and Hewlett, 1982 for reviews). These experimental catchment studies were very common in the 1960's and have since developed to include the study of sediment transfer mechanisms and other physical processes associated with hydrological impacts of forestry activity. In addition, the focus has shifted from being purely hydrological to being more integrative by examining impacts on biogeochemical processes. The following discussion of existing literature focuses on three areas. Water yield, which is affected by the change in water balance associated with clearcutting, is first discussed as it is an important factor in determining sediment mobilization and transfer. Studies of suspended sediment concentrations are then reviewed as they explore the relation between timber harvesting operations, enhanced surface erosion and suspended sediment yields. Lastly, the effects on lacustrine sedimentation are highlighted. 2.3.1. Water Yield Decreases in evapotranspiration and canopy interception associated with removal of forests lead to increased water yields in proportion to the extent of harvesting and reduction of basal area (Hornbeck et al, 1993). Hydrological response to disturbance persists for no longer than ten years following impact unless vegetation regeneration is delayed through the use of herbicides. While increases in water yields are apparent in most cases, the magnitude of the response depends largely on precipitation and forest cover (Whitehead and Robinson, 1993). Thus, the response may be more significant in coastal British Columbia where high precipitation and big trees are common (Church, 1996). Other factors which determine the nature of water yields following harvesting are snowmelt runoff and fog drip. The latter is most likely significant in Clayoquot Sound and Barkley Sound. The loss of fog drip with the removal of vegetation may 23 offset the expected increase in water yield (Harr, 1982). Church (1996) suggested that increases in water yield are most apparent in the early autumn when the contrast in soil moisture between a clearcut area and a forested area would be most significant, although increases in summer low flows are also apparent. The nature of harvesting operations also affects the nature of the hydrological response. Hornbeck et al, (1993) emphasized the configuration of cutting as another important factor in determining the magnitude of the response. Timber harvesting in strips or of individual trees leads to increased crown exposure and transpiration rate of residual trees. This reduces soil moisture content, and leads to lower water yields. Timing of logging is also important, pointing once again to the influence of existing soil moisture on stream flow (Hornbeck et al, 1993). While there is consensus on the effects of forestry on annual water yields, hydrological response during extreme events is less clear (Whitehead and Robinson, 1993). The variability in stormflow response has been revealed by several case studies. Harr et al (1975) analysed storm hydrograph parameters of paired catchments in the Alsea watershed of Oregon: peak discharge increased following timber harvesting. They also identified seasonal fluctuations in peak discharge related to soil moisture content. High moisture contents in cleared areas promote higher responses than in forested areas where soil moisture is depleted throughout the growing season. Peak flows related to rain-on-snow events, which are common in coastal British Columbia, behave differently. Canopy interception facilitates snowmelt so that removal of vegetation can lead to decreased peak flows (Church, 1996). Jones and Grant (1996) examined changes in peak discharges, volumes and timing in small and large basins with clear-cutting alone, with roads alone and with both roads and clear-cutting. Their study emphasized the role of roads and clear-cutting in altering the nature of the drainage 24 network of a watershed. Jones and Grant (1996) found that peak flows increased in all cases. In contrast, some studies reported no changes in peak flows following harvesting (see references in Church, 1996). However, it is clear that timber harvesting operations alter the landscape in ways which are significant for the generation of stormflow hydrographs. The nature of the subsequent change is dependent on the interaction of a number of factors, some of which are the type of precipitation, the time of year and watershed elevation (Church, 1996). 2.3.2. Suspended Sediment Yield Much work has been done in characterizing the effects of timber harvesting operations on the suspended sediment concentrations in streams due to the implications for fish habitat and water quality of downstream reservoirs. Brown and Krygier (1971) working in the H. J. Andrews experimental forest, in Oregon, found that there was a 5-6 year recovery period following increases in sediment yield resulting from forestry activity. They stressed the variability of the response between watersheds and the importance of extreme events on annual sediment yields. In addition, they found roads to be the primary source of sediments, followed by the exposure of mineral soils following intense burning of slash. Beschta (1978) analysed the long-term effects of forestry in the Alsea Watershed, Oregon, focusing on the timing and magnitude of fine sediment production. Increased sediment yields and suspended sediment concentrations related to road surface erosion remained high for 3 out of 8 post-treatment years. Blackburn et al. (1990) reported similar findings for watersheds in East Texas, distinguishing between the effects of several kinds of site preparations and post-clearance land-uses. In the context of regional trends however, observed sediment losses were within the range of both disturbed and undisturbed sediment yields in the area. Sediment yields in the Kirkton watershed at Balquhidder, Central 25 Scotland, increased 600 % from former levels as a result of deforestation (Johnson, 1993). In the Carnation Creek study, Vancouver Island, fine sediment concentrations were most sensitive to episodic releases of substantial volumes of fine sediments associated with the failure of log jams and mass movements (Church, 1995). However, the scope and resolution of research to date does not permit an assessment of the role of logging activity in these processes. Roads have long since been identified as the major source of suspended sediment yields in catchments experiencing forestry activity. Reid and Dunne (1984) identify two major aspects of this problem: how much sediment is mobilized by road surface erosion and what is the relative importance of road surface erosion compared to other road-related sediment sources? In terms of the first question, traffic intensity in their field study is key in determining the magnitude of sediment production. Heavily used roads (>4 logging trucks/day) produced 100 times more sediments than an abandoned road (Reid and Dunne, 1984). In addition, road surfaces were much more important than cutbanks or ditches as sediment sources. Other sources of sediments related to roads were landslides from road fills and sidecast material, debris flows (starting as landslides) into stream channels, sediment sidecast where dry ravel and rainsplash mobilize fine sediments, and road cuts (Reid et al, 1981). A sediment budget approach defined the relative importance of each sediment source. Sixty percent of road-related sediment production was attributed to landslides, while twenty percent came from road surfaces (80% of which comes from highly-used roads). Reid et al. (1981) also recognized the influence of roads on altering the nature of the drainage network, which in turn affects the mobilization of fine sediments and downstream sedimentation. Another important source of suspended sediments are slides on open slopes. While a clear relation between slides and forestry activity remains to be established, studies have shown that the 26 occurrence of slides may increase significantly following timber harvesting (Church, 1996 and references therein). Failure is not necessarily immediate however, and may occur up to 5-10 years after timber harvesting. This lag effect is attributed to residual soil strength from slow root deterioration. The relations between forestry activities and water yield and suspended sediment concentrations outlined above are drawn from studies conducted in a variety of environments and thus the general magnitude and direction of the response is likely to be valid for British Columbia. However many of these studies were conducted in physical environments which differ from coastal British Columbia. Local conditions will affect the response observed in the study region. The deeply weathered soils of the unglaciated landscape of Oregon and Washington for example stand in contrast to the shallow soils which have developed on extensive blankets of glacial drift in British Columbia. The hydrological response to harvesting may be greater in British Columbia due to the low water storage capacity of shallow soils (Church, 1996). 2.3.3. Effect of Forestry Activity on Lake Sedimentation It is evident from the review of literature above that changes in discharge and sediment concentrations have been observed. Although the response may be complex, it is assumed that forestry effects will be recorded in lake sediments. Both traditional studies of environmental reconstruction and studies of erosion and sediment yield associated with land use activities have documented changes in the nature of the sediments delivered as well as changes in sedimentation rates associated with forest clearance. Forest clearance, often followed by agriculture, is not directly comparable with the forestry activity in the current study area as the latter includes replanting and regrowth of the forest cover. However, specific examples of lake-based studies of 27 deforested basins illustrate the relevant issues, techniques available, and the wide range of sediment properties used to identify the effects of a change in forest cover. In many long term studies, mineralogical and sedimentological evidence supports palynological evidence of vegetation cover changes related to human disturbance. A decline in arboreal pollen which precedes layers of pedogenic origin, was interpreted as evidence of widespread basin erosion during the mid to late Holocene (Laval et al., 1991). The erosion was linked to forest clearance as subsequent layers revealed the presence of pollen associated with the development of agriculture. In a similar study, Kremenetsky (1995) identified periods of accelerated erosion through an analysis of the pollen record and of sedimentation rates in two swamps in the Southwestern Ukraine. In this case, palynological and historical records, and the increase in sedimentation rates provided the evidence for the interpretation. The time scale of change is on the order of 102-104 years (some studies cover changes caused by ancient civilizations) and the record of vegetation change can only resolve major shifts in vegetation cover. This level of resolution is typical of Quaternary and Holocene studies. This shortcoming is, to a large extent, absent in studies of erosion and sedimentation associated with more recent human activity. The pollen record of two cores from Lake Washington was examined and compared with established historical records of land-use changes (Davis, 1973). An increase in sediment accumulation was recorded from 1890 to 1916 while, according to the historical record, large scale logging around Seattle began in 1880. Lag effects such as this one are an integral part of impact studies and are not considered further by Davis. While the study illustrates the value of a thorough review of historical records in interpreting the sediment record, it is based on only two cores, prohibiting a drainage basin scale interpretation of sediment yield associated with surface erosion and logging activity. Davis (1976) presented 28 further evidence of increase in sediment yield from forest clearance. The sedimentary record of Frains Lake spans from 1770 to the present allowing pre-clearance erosion rates to be established and compared with erosion rates associated with forest clearance and crops. This illustrates the contextual analysis of sediment yield Bathurst (1994) was advocating in his criticism of stream-based sediment yield studies. Two studies identify sedimentological properties associated with human disturbance in particular physiographic regions. Decreases in organic content and increases in magnetic susceptibility, inorganic silica and cations associated with volcanic soil are interpreted as representing periods of accelerated erosion in the highlands of Central Mexico (O'Hara, et al, 1993). Rates of sedimentation during episodes of erosion are estimated to be between 10, 300 t/yr between 2500 and 1200 years before present and 29,000 t/yr in the last 850 years. The latter value coincides with the rise of the Postclassic Purepecha Empire, which is known for ceremonial bonfires and the manufacture of various forest products. In the tropical karst environment of Haiti, Brenner and Binford (1988) documented the onset of deforestation with palynological evidence. Decreases in organic matter content and increases in carbonates record consequent erosion. While many studies have focused on enhanced surface erosion and the resulting increase in lake sedimentation rates, very few studies have considered the effects of forest clearance on autogenic sediment sources. Almquist-Jacobson etal. (1992) assessed the influence of vegetation cover of the surrounding catchment on sediment-forming processes in kettle lakes of West-central Minnesota. Changes in organic, inorganic and carbonate sediment deposition rates as well as changes in sediment magnetic characteristics were observed during succession from pine forest to prairie environment. Almquist-Jacobson et al. (1992) suggested that wind exposure affects influx 29 of eolian particles, erosion of shorelines, water circulation and carbonate equilibria. Upland vegetation affects soil water chemistry, evapotranspiration and soil moisture and thus the chemical nature and amount of groundwater input to the lake. This characterization of relevant processes contributes to the understanding of the link between vegetation cover and lacustrine sedimentation. While a study of alternative sediment forming processes similar to that of Almquist et al. (1992) is beyond the scope of this thesis, they should be considered as they may contribute to the accumulation of sediments related to clear-cutting practices. 2.4. DISCUSSION A critical review of work done on lake sedimentation and the effects of forestry reveals several areas requiring further research. The consideration of human impact in studies of environmental reconstruction is relatively rare in North America because significant impacts are much more recent than the periods typically covered in such research. Most studies in Eurasia suffer from a lack of historical and archeological records of early civilizations. As a result, studies of environmental reconstruction mention human impact only briefly. The impact of European settlement in North America is often recorded in lake sediments with an increase in Ambrosia and a decrease in arboreal pollen (Almquist-Jacobson etal, 1992). However, this is often used as a chronological marker signalling the end of the period being studied rather than a particular area of inquiry. Moreover, the purpose is to reconstruct vegetation change throughout the Holocene rather than to reconstruct the impact this change may have on the sediment regime. The relatively recent development of large-scale logging in North America and the general emphasis on Holocene rather than contemporary reconstructions from lacustrine records in North America may explain the relatively few indications that have been found of the effects of forestry on lake 30 sedimentation. One of the main barriers is the issue of resolution. In traditional studies of environmental reconstruction from lake sediments, there are no existing records of vegetation changes and therefore no independent assessment of those vegetation changes can be carried out. The inferences are then limited by the degree of confidence in the established chronology and the ability to isolate the cause of changing sediment properties. In contrast, erosion and sediment yield studies compare historical records of land-use changes (e.g. agriculture) with the record of change in lake-bottom sediments. This is potentially a much more sensitive analysis, assessing rapid changes on much shorter time scales. Furthermore, the correspondence between the chronology of the sedimentary record and the historical records of disturbance allow better chronological control in the interpretation of the catchment change and the corresponding response. Studies of the effect of forestry activity on lake sedimentation are in general limited. None have been completed in coastal British Columbia and very few cover time scales of less than 100 years. Issues of sediment source, upstream storage and lag effects identified in studies of the effects of other types of land-use need to be addressed in the context of forestry activity and lake sedimentation. Chapter 3 Methods 31 3.1. INTRODUCTION Retrieval and analysis of sediment cores from 4 lakes was undertaken to explore questions of sedimentation response to forest harvesting. One lake was used as a control, while the others lake basins are logged to various degrees. Site selection involved consideration of the similarity of basins, and their suitability for a lake-based sediment yield study. Topographic maps and air photos of the region were examined to establish a list of candidate lakes. Field reconnaissance determined ultimate suitability of the lakes. Field sampling of lake cores and subsequent laboratory analysis of sediment established the temporal and spatial variability of the nature of sedimentation and of sedimentation rates. There are three steps to assessing change in the nature of lake sediment and relative rates of lake sedimentation. The first is to establish the physical and chemical properties of the sediment. Relative downcore changes of physical properties provide fundamental information to infer past catchment conditions. Analyses which establish sediment composition (organic content, diatom or biogenic silica and carbonate content) and bulk density are also essential to convert volumes of sediment into mass-based clastic sediment yields! The more complex methods to determine sediment geochemistry and particle size provide additional information for the interpretation of past conditions. The second component of lake sediment studies is to date the sediments and establish a chronology of sediment deposition. The radioactive isotopes lead-210 (^ "Pb) and caesium-137 (137Cs) were used to this end. The third step entails using some of these properties to cross-correlate cores within lakes, in order to calculate whole-lake sediment accumulation and catchment sediment yield. The sediment record was examined in all basins over a period that 32 commences well before forest harvesting. Terrestrial surface materials were collected to resolve issues of sediment source. Ancillary data such as bathymetric surveys and shoreline surveys provide basic morphometric and geomorphological information about each study lake. While the analysis of the lacustrine sediment record is the focus of the study, the development of methods for the analysis of recent sediments is also an integral part of the study. Thus, methodological considerations particular to this time scale are highlighted wherever relevant and discussed more at length in the section entitled "subsampling strategy"(section 3.4.2). 3.2 SELECTION OF STUDY SITES 3.2.1. Selecting Comparable Basins General criteria for the selection of comparable basins include: contiguity, geological and physical similarity and uniform vegetation (Church, 1984). The definition of contiguity adopted for this study is "that they be contiguous if they are within 50 km of each other". Contiguity is an important criterion because it ensures that basins are experiencing similar climate, which eventually influences surface erosion rates and the frequency of mass movement events. Geology affects erosion rates and sediment yields. Physical characteristics of a basin (elevation, slope, area, catchment to lake ratio, drainage density and relief) not only affect erosion rates, but also influence sediment routing, sediment deposition and vegetation. Vegetation, in turn, also affects erosion rates, sediment routing and sediment deposition. Distance from the coast was particularly considered to minimize the difference in patterns and type of precipitation associated with distance from the Pacific Ocean. All of the above criteria were considered in the first phase of the selection process. 33 3.2.2. Selection of Lake Basins The ideal lake for this type of study is steep-sided and fairly deep (20+ m) to minimize the potential for physical reworking of sediments from waves, seasonal overturn processes, lake level fluctuations, subaqueous slumping, and bioturbation by bottom dwelling organisms (Dearing and Foster, 1986). High sediment accumulation rates, simple lake morphometry, and high trap efficiency are also preferable (Berglund, 1986). High sedimentation rates provide longer cores from which to analyse sediment properties, thereby providing resolution on the order of several years to a decade to estimate short-term sediment accumulation rates and to resolve changes in physical and chemical sediment properties. Complex bottom morphology leads to substantial spatial variations of sedimentation patterns, making estimates of sediment yield for the whole basin problematic. Bottom roughness, can be deduced from the degree of crenulation of the shoreling of a lake (Hakanson and Jansson, 1983) or from depth sounding with graphical output. High lake trap efficiency is preferable because longer residence times and minimal loss of sediment from outflow produce better sediment records. The local bedrock geology were considered to deduce the nature of outflow losses. Finally, the time span over which forestry activity took place was an important factor to consider during the site selection process, as longer records with a distinct response following disturbance are preferred. A long record following disturbance allows a sedimentation response to be recorded despite lag effects due to residual soil strength and temporary upstream storage of sediment in transport. Furthermore, when forest harvesting occurs over a relatively short time span, the response is expected to be relatively distinct. In contrast, varied and prolonged forestry activity will probably be harder to detect as sediment production may increase in limited areas and at different times within the lake basin. These two criteria, time since initial disturbance and 34 duration of logging activity, were often at odds as areas where logging started early (1950's) on the west coast of Vancouver Island are also the areas with the most prolonged history of disturbance. 3.2.3 Topographic and Air Photo Survey A list of candidate lakes with comparable basins was first established by noting the following characteristics for over 100 lakes: size and shape of lake, surface elevation, topographic gradient near the lake and throughout the contributing catchment, number of inflowing and outflowing creeks, road access, and general orientation of the lake. A list of approximately twelve sets of lakes on the Sunshine coast and on the central west coast of Vancouver Island was extracted from this preliminary survey by establishing contiguous lakes with similar topography and drainage. Review of air photos shortened the list to eight sets due to inaccessibility of some lakes, and lakes without a control unlogged basin or without a logged basin. These lakes were ranked according to the following five criteria: similar topography, similar drainage density, contiguity, distance from the coast and ease of access. 3.2.4. Field reconnaissance Final selection was made during two field trips through an assessment of morphological characteristics and accessibility of the eight sets of lakes. Three lakes on the West coast of Vancouver Island were investigated using preliminary depth sounding and Ekman grab sampling of bottom sediments. This revealed that all three lakes are deep and steep-sided, and have relatively simple bottom morphologies. Their logging histories are quite varied in terms of the onset of clearance and the extent to which each basin is harvested. This provided an opportunity 35 for cross-comparisons and analysis of the effects of a variety of logging histories. All three lakes were therefore selected for further study. The lake selected as a control to these logged basins is accessible only by air and was therefore not visited on this reconnaissance trip. 3.3. CORING OF L A K E SEDIMENT Coring of lake bottom sediments was the main component of the field work. Various coring devices and sampling strategies have been designed for the extraction of subaqueous sediments (see Lowe and Walker, 1984; Aaby and Digerfeldt, 1986; and Goudie, 1981 for reviews of existing techniques). Several corers were tested to select the coring technique suitable for the sediment type encountered in the Ekman samples. The modified Livingstone sampler (Livingston, 1955; Schmok, 1986; Souch, 1990, and Evans, 1993), a piston corer which works well with fine sediments, can only be used in shallow lakes due to its reliance on rods for its operation. The Phleger coring device was used during field reconnaissance, but the highly unconsolidated nature of the sediment made it inadequate to successfully retrieve sediment from the selected lakes. A freeze corer (Huttunen and Merilainen, 1978 and Schmok, 1986) was also considered due to its ability to preserve high resolution laminated records. Its use was discounted however, for logistical reasons and on the basis of the lack of visible laminations in the Ekman samples. Coring for this study was undertaken using a modified Kajak-Brinkhurst gravity corer (Brinkhurst, 1974; Fig. 3.1). The release of a seal at the top of the core barrel, once the corer has penetrated the sediments, allows extraction of cores without the use of a core catcher. This prevents alteration of the outer surface of the core, which was especially significant for the removal of these soft, under-consolidated, organic-rich sediments (Stephenson et al, 1996). The Figure 3.1: Coring apparatus. 37 lightweight design of the corer also permits easy retrieval of short sediment cores from depths up to several hundred metres. An A-frame support system was build to facilitate core retrieval (Fig. 3.1). Initially designed to handle the much heavier Phleger corer, it was easily modified to facilitate the retrieval of the K-B corer. Coring density in various lake sediment studies varies significantly (Foster et al, 1990). Optimal coring density depends on the purpose of the study, size of lake, complexity of the lake bottom morphology, and amount of time and effort available to characterize anticipated variability of depositional environments. A coring density of 1 core per 0.1 km2 used in one of the studies documented in Foster et al, (1990) was deemed adequate to characterize sedimentation variability across the four lakes. Coring location was based on depth sounding data to include sub-basins and areas of maximum depth, thereby capturing variable sedimentation patterns and areas of maximum accumulation. Core locations were established from landmarks visible on air photos. Clear acrylic core barrels (2.5 inches inner diameter) were removed from the coring device, sealed with rubber stoppers and wrapped for storage to allow subsequent whole-core analysis of magnetic susceptibility. Cores were described in the field in terms of sediment texture (fine versus sand), colour (e.g. grey, buff, brown), type of organic content (fibrous, wood chip, needles, twigs), contact between noticeable layers (sharp, undulating, graded, loaded, continuous, irregular), and nature of the sediment water interface (disturbed, presence of chironomid tubes). Using long stemmed pipettes, water was removed from the top of cores. Cores were then dried to a working consistency before placing them in cold storage. 38 3.4. LABORATORY METHODS 3.4.1. Whole-Core Analysis Prior to applying procedures to specific sediment samples, two whole-core analyses were carried out. Magnetic susceptibility scans were accomplished at 5 cm interval. This procedure established that there was variability in this parameter and that specific susceptibility of sediment at shorter intervals (1 cm) was required to obtain a better resolution of its variation over time. Experimental x-radiography of a trial core indicated that sedimentary layers are best resolved from frozen sediment slabs of uniform thickness. Furthermore, the technique used in medical mammography generates better exposures than standard x-ray techniques (Technical specifications: a Senograph 600T, an aluminum target, settings at 27 KV, 25 mAs and Kodak Min-R film). All cores were therefore frozen and cut lengthwise to produce a 1 cm thick slab. Contact prints of all x-rays were made to allow scanning of x-rays into a photo software program. The sediment slabs were wrapped in cellophane and foil for freezer preservation. This visual archive was used to devise the optimum subsampling strategy for subsequent analyses. 3.4.2. Sub-Sampling Strategy While most of the laboratory techniques have been developed by others, many had to be modified to accommodate the relatively short period of interest in the cores. Assuming a sedimentation rate on the order of 1 mm/year typical of Vancouver Island lakes (Rick Nordin, pers. comm., 1997), the first 10 cm should represent most of the period of European settlement. To obtain high resolution in sediment properties during the last 100 years, a small sampling interval is required. Every effort has to be made to maximize the use of the restricted amount of sediment available in each sampled layer. Various trials of different techniques were undertaken 39 to derive the most suitable sub-sampling strategy and set of procedures (Table 3.1). All cores were cut parallel to sedimentary layers at 1 cm intervals using a vertical band saw. This was the smallest interval possible considering the core diameter, the cutting method used and the minimum amount of sediment required for analyses. All cores were analyzed at 1 cm resolution for the following physical properties: bulk density, total residual moisture content, organic content and magnetic properties. One core in Maggie Lake (M10) and one in Toquart Lake (T5) were not analyzed since x-ray images revealed a highly disturbed sediment record. As little as 5 g of sediment is obtained from 1 cm intervals which is not sufficient for all analyses to be carried out, especially since most procedures are destructive (see Table 3.1). The more labour-intensive and costly techniques (absolute dating, sediment geochemistry, particle size, diatom and carbonate content) were carried out on a subset of cores selected from each lake (see Table 3.2). These cores were extracted from either a central location to incorporate maximum sedimentation rates or from the centres of lake sub-basins to consider the spatial variability in patterns of sedimentation. Where possible, additional cores strongly correlated with the central core on the basis of organic content and x-radiographs were selected to allow all the more complex techniques to be carried out at a 1 cm resolution (Table 3.3). This was deemed the best strategy because alternating analyses every other centimetre on one core and thus sampling at a larger interval (e.g. 2 cm interval) would compromise the interpretive power of the study. Both master cores and matched ones were analyzed at stratigraphically significant depths or at 2 cm intervals to establish the general downcore pattern. Further analyses were 40 Table 3.1: Summary of laboratory analyses outlining number of cores analyzed, whether or not the analysis is destructive, the sampling interval and the amount of sediment required for the analysis. ANALYSIS #OF CORES RECOVERY POTENTIAL SAMPLING INTERVAL AMOUNT OF SEDIMENT REQUIRED Whole-core magnetic susceptibility all non- intrusive 5 cm whole core in barrel Mammography x-ray all archived n/a frozen sediment slabs (1 cm thick) bulk density / residual moisture content; hygroscopic moisture all full recovery 1 cm whole sample layer; ~1.0g Organic content (LOI) all recovered for carbonate and geochemical analysis 1 cm - 1.0 g from above Magnetic properties: specific magnetic susceptibility and saturated isothermal remanent magnetization (SIRM) all non- destructive 1 cm sample cylinders must be filled and sediment compacted, ~5-8g Carbonate content subset destructive irregular - 1.0 g left from LOI Geochemistry subset destructive stratigraphic markers / irregular - 1.0 g LOI sediment Particle size subset non- destructive 2 cm ~4g Diatom or biogenic silica content subset destructive 2 cm ~2g Caesium-137 activity subset non-destructive stratigraphic markers / irregular - 3-4 g in glass vials Lead -210 activity subset destructive 2 cm -0.25 g for the top 5 cm, -1.0 g for 5-10 cm depths, and -1.5 gfor 10+cm. Note that each sample layer is 1 cm thick, las a diameter of approximately 3 cm and 3-8 g of sediment. Assuming a sedimentation rate on the order of 1 mm/yr, the temporal resolution of each sample varies between 10-20 years. Weights of sediment refer to oven-dry (at 40°C) weights, unless otherwise stated. 41 carried out once the need for higher resolution was assessed and if downcore variability in a certain property was high. Table 3.2: Summary of cores processed for the more complex analyses. (M- Maggie Lake, T-Toquart Lake, K- Kite Lake, and C- Clayoquot Lake). ANALYSIS CORES PROCESSED 137Cs activity M5,M16, M11;T10;K2;C1 210Pb activity M5, Ml6, Mil ; T10, T2; K2, and CI Geochemistry M18, M12, T9, C3, * Carbonate content M5, M12 and M8; T8, T4; Kl; C2 Diatom or biogenic silica content Ml8, Ml2, T9, C3,K2 Particle size M18,M12, T9, C3, * *A Kite Lake core was not analyzed due to insufficient sediment in core K2 and the restricted length of cores Kl and K4. Table 3.3: Master cores matched for sampling. L A K E MASTER CORES MATCHING CORES Maggie M5,M11 M18, M12 Toquart T10 T9 Kite K2 n/a Clayoquot CI C3 Master cores were analysed for 137Cs concentrations at irregular intervals until the 1963 peak and the onset of the rise in 137Cs activity were resolved at maximum resolution (1 cm). The activity of 210Pb was assessed on all master cores at 2 cm intervals. Additional cores were dated in Maggie and Toquart Lake (Ml 6, Ml 1, T2) since the former is quite large and the latter consists of two well-defined sub-basins (see Table 3.3). Core T2 was dated using only 210Pb because cores across the upper and lower basin of Toquart lake are well correlated based on organic content. Thus, lead-210 analysis of T2 was deemed sufficient to establish the 42 synchroneity of stratigraphic markers identified in the upper and lower basin. Located across from highly-gullied logged adjacent slopes, core Ml 1 is thought to record recent mass movement activity. As a result, its specific chronology provides an opportunity to study the direct impact of mass movement related to forestry activity on lake sedimentation. Utilization of both caesium and lead isotopes provides a means to cross-check the developed chronologies. While 137Cs and 210Pb activity was assessed from master cores, sediment geochemistry, diatom content and particle size were assessed on cores highly correlated to these central cores (Tables 3.2, 3.3). The percentage of carbonate sediment was established in cores which were not necessarily strongly correlated with the central core since this parameter is thought to be relatively constant across these lakes. Several cores were analyzed in the bigger lakes and the results support this assumption. In summary, the subsampling strategy described above provides a means to assess variability of sediment characteristics across each lake while taking into consideration the short supply of sediments per sample layer. It also ensures that sediment properties can be determined at 1 cm intervals if necessary. 3.4.3. Bulk Physical Properties A three step process allows the measurement of bulk density, total residual moisture content and organic content (Berglund, 1986; Gale and Hoare, 1991). Each frozen sample was cut with a custom-made heated aluminum sampler to repeatedly sample a known volume. The known volume of each sample was then air dried for 12 hours at 40°C to remove moisture. Additional oven drying at 105° C for 12 hours of a disaggregated sub-sample (1 g) removed 43 hygroscopic moisture. This two step-drying process is necessary as magnetic analyses require 5-8 g of sediment dried at no higher than 40°C. Total residual moisture content is the percent weight lost during both drying periods. Bulk density is the oven dry weight of the known frozen volume divided by that frozen volume. Organic content was established using standard Loss on Ignition technique (Dean, 1974; Gale and Hoare, 1991) where weight loss is determined after four hours in a 500°C furnace. This parameter is expressed as % of the oven dried weight. The replicability of the above procedures was tested using four sets of three replicates from various downcore depths. The bulk density procedure can not be replicated as only one sample of known volume could be cut from each 1 cm layer. Replicate analysis shows 0-0.4% difference in the measurement of hygroscopic moisture (Table 3.4). The measurement of organic content was least precise in replicates of Kite samples with a 3% difference. This is most likely due to the high concentration of macro-organics, the combustion of which may have varied. Differences of 0-1% are reported for the measurement of organic content in other replicates. 3.4.4. Magnetic Properties Sediments dried at 40 °C and disaggregated were sieved to isolate the <2 mm particle size fraction and packed into plastic sample cylinder (6.3 cm3). Magnetic susceptibility of each sample was first measured on a Sapphire SI2 susceptibility metre (noise level: 10"5 SI/vol). Saturated isothermal remanent magnetization (SIRM) was then measured on a Geophyzika JR5A magnetometer (noise level: 5 x 10"6 A/m) following saturation in a 1 Ampere electromagnetic field. This procedure is non-destructive allowing sediment to be used again. 44 Table 3.4: Results from replicates of measurement of hygroscopic moisture, organic content and carbonate content. Core and samnle id Depth rcml %Hygroscopic moisture % organic content %C03 K4-4a 3.85 3.1 20 1.5 K4-4b 3.85 3.2 21 1.7 K4-4c 3.85 2.7 18 1.6 K4-%difference 0.5 3 0.2 T8-10a 10.45 3.3 19 1.6 T8-10b 10.45 3.5 19 1.7 T8-10c 10.45 3.6 19 1.7 T8-%difference 0.3 0 0.1 C2-15a 15.95 3.8 24 2.0 C2-15b 15.95 3.8 25 1.9 C2-15c 15.95 3.8 24 1.9 C2-%difference 0.0 1 0.1 M17-20a 21.45 2.4 14 1.5 M17-20b 21.45 2.5 14 1.5 M17-20c 21.45 2.4 14 1.5 Ml 7-%difFerence 0.1 0 0.0 3 . 4 . 5 . Determination of Autochthonous Sediment Fraction Carbonate content is calculated by dividing by 0.44 the percent weight loss from C0 2 released when sediment is subjected to 900°C for an hour (Dean, 1974; Bengtsson and Ennel, 1986). Some organic matter may ignite at this temperature and some carbonates may have ignited during the LOI procedure at 500 °C. The carbonate concentration is used in the calculation of sediment yield in combination with organic content and biogenic silica, thereby making this possible source of error irrelevant. The method is deemed adequate to characterize downcore variability as the same procedure was adhered to with each sample. Replicability was established using four sets of three replicates taken at various downcore depths (Table 3.4). Diatom or biogenic silica content is based on weight loss associated with alkaline digestion 45 of the sample. Dry sediments were first treated with 30% hydrogen peroxide to remove organics (Gale and Hoare, 1991). Samples with high concentrations of macro-organics were dry-sieved at 1000 /urn to facilitate the peroxide treatment. The residue was dried, disaggregated using a pestle and mortar, and reweighed before being heated in 50 ml of 0.2 M sodium hydroxide for an hour at 95 °C (Engstrom and Wright, 1984). After cooling, the solution was filtered through pre-weighed filters (0.45 /urn Sartorius cellulose nitrate membrane filters). Weighing filters before filtration required oven drying (at 105°C) for an hour and cooling in a desiccator for an hour. The residue on the filter was dried and weighed to establish the weight of biogenic silica lost in the alkaline digestion. 3.4.6. Sediment Geochemistry The concentrations of the following total recoverable elements were established at stratigraphically significant markers: sodium, potassium, manganese, iron, magnesium, calcium, silica and aluminum. The heavy metals zinc, cadmium, chromium, nickel, lead and copper were also extracted. The analysis involves acid digestion following US Environmental Protection Agency methods (Office of Research and Development, U.S. Environmental Protection Agency), and measurement with a Jarrell Ash Inductively Coupled Plasma (ICP) Spectrometer and an Atomic Absorption Spectrophotometer. Standards from the National Research Council of Canada (reference materials MESS-1 and BCSS-1) were used to establish the level of accuracy, while 10% replication of each set of analyses was maintained to establish the precision of the measurements. Precision levels for geochemical analyses are reported with each set of results in chapter 5. 46 3.4.7. Particle Size Analysis Particle size distribution was established using a Micromeritics SediGraph 5100 system. Samples were first treated with 30 % hydrogen peroxide to remove organic matter. Samples with high concentrations of macro-organics were dry-sieved at 1000 fj.m to facilitate the peroxide treatment. The sample was left overnight in dispersant (10 ml of 0.05 % sodium metaphosphate) before wet sieving through a 63 jum sieve. Material greater than 63 tim (sand) was collected from the sieve, dried at 105°C and weighed. The material less than 63 //m (silt and clay) was dried at 40 °C (to avoid clumping of clay), disaggregated and weighed prior to analysis. Dispersant was added to the samples to ensure the disaggregation of clays. Sample size did not permit division of the sand fractions. 3.4.8. Sediment Dating The lead-210 (210Pb) isotope was measured by the radiochemical purification of its grand daughter isotope, Polonium-210 (210Po). In sediments, the concentration of 210Po is equal to that of 210Pb. Po-210 was measured by isotope dilution alpha spectrometry (Eakins and Morrison, 1978). In this process, a known amount of209 Po was added to the dried samples of sediment. Various sample sizes of dried sediment were required downcore to account for the decreasing level of 210Pb activity (Table 3.1). The Polonium isotopes were then extracted from the sediment matrix by digestion in hot aqua regia (HC1 / HN03). The HN03 was evaporated, a reducing agent added to reduce oxidants that might interfere with the electroplating and the two isotopes of Polonium were electroplated onto silver disks in a dilute solution of HC1 (Millard, 1963; Flynn, 1968). The quantity of each isotope was determined by alpha spectrometry using silicon surface 47 barrier detectors. The activity of 210Po in the sample was determined from the ratio of the total counts of Po-209 : Po-210 and from the quantities of sediment and Po-209 added to the sample. Details are presented in Evans and Rigler (1980) with modifications described in Cornett etal., (1984) and Rowan et al, (1995). The concentrations of 210Pb were interpreted using the constant rate of supply (CRS) Pb-210 dating model (Appleby and Oldfield, 1979; Robbins, 1978). Total activity of 210Pb in sediment is comprised of excess (unsupported) 210Pb from the catchment and the atmosphere, and supported 210Pb which is in equilibrium with Ra-226. The CRS model assumes that the input of excess 210Pb to the sediment-water interface has remained constant through time and that no post-depositional migration of the radionuclide has occurred over the dating interval. This model allows for fluctuations in the deposition of sediment over time, and is therefore deemed best suited for this study (Appleby and Oldfield, 1983; Olsson, 1986). The total quantity of excess 2l0Pb was used in the determination of sediment ages. The age of a section of a sediment core was calculated from: Age = Age(0) - L"1 • In (S / SJ where age is expressed in years, Age (0) is the year the core was collected, L is the decay constant for 210Pb in years, S is the total quantity of excess 210Pb in the core, and S; is the quantity of excess 210Pb below depth (i). Cs-137 concentrations in sediment samples were determined with APTEC gamma spectrometric facilities. Samples had to be homogenous, disaggregated and free of macro-organics (1000 /urn dry-sieve). HPGe detectors have resolutions between 1.8 and 2.6 keV and relative efficiencies between 10% and 20%. Data analysis was performed using a 486 AMPAQ computer and the APTEC spectrum analysis program (APTEC, 1993). Efficiency calibrations 48 made use of 1 3 ,1, 1 0 9Cd, 133Ba, and 65Zn solutions. The IAEA-375 intercomparison sample was used to check the efficiency of the calibration. Measured values were well within the confidence interval (less than 2% difference for the recommended value). The maximum in Cs-137 activity corresponds to the year 1963, while the onset of the rise in activity corresponds to 1954 (Ritchie and McHenry, 1990). 3.5. CROSS-CORRELATION ANALYSIS AND SEDIMENT YIELD CALCULATION Core correlation was based on a combination of parameters (organic content, magnetic properties and x-ray grey tone). Trends in these parameters and visual similarity in the x-ray images were used to identify synchronous levels in cores throughout each lake. Zones were then defined chronologically using the correspondence between the results of the two sediment dating analyses. Dry sediment mass between date markers was determined using bulk density data. The proportion of organic matter, biogenic silica and carbonate was subtracted from the sediment mass, allowing the sediment influx within dated zones to be converted into allogenic clastic accumulation rates in each core (Dearing, 1986). The calculation of whole-lake sediment accumulation for synchronous zones (in all cores) takes into consideration the area which each core represents within the lake. A critical depth of 10 m was adopted for the definition of the area of the lake which experiences sediment accumulation. It is assumed that areas above the 10 m depth contour are characterized by erosion and transportation of sediment. The area which a core represents was then defined using Thiessen polygons (O'Hara, 1993) and calculated using digital planimetry. If a zone was not represented in one or more cores, Thiessen polygons were redefined, and areas recalculated to accommodate the 49 lack of data at that point. The exercise was repeated assuming a critical depth of 20 m to test the sensitivity of sediment yield to this assumption. Lastly, lake trap efficiency was determined to account for outflow losses and thus convert whole-lake sediment accumulation into catchment sediment yield. Mean annual flow was determined for each basin using the equation: wherein Q is the mean annual flow for a specific area, k is the unit hydrological estimate for the region i, and Ad is the drainage area (Church, 1997). The k value for the study region is 0.15 ± 0.10 (Church, 1997). Trap efficiencies were determined on the basis of this range in discharge, Brune's curve (Brune, 1953) and the equation of Brune's curve for fine sediments derived by Gill (1979). Upper and lower limits of the sediment yield estimates are based on the confidence range of kj and the two critical depth values which affect the area that each core represents. Sediment yield is normalized by drainage area and expressed in t km"2 yr'1. 3.6. BATHYMETRIC SURVEY Basin morphology was established from bathymetric soundings with graphical outputs. Depth sounding was executed using an Apelco Ranger 420 Echo Sounder along a number of transects. Time was recorded throughout the surveys to control the effect of boat speed. Depth data were extracted from the echo sounder's graphical output and bathymetric maps were produced manually for each lake. A qualitative analysis of the bottom morphology was undertaken noting slope, bottom topography, maximum depth, core location, turbidite evidence, nature of the depth sounding signal and its possible interpretation. The definition of depositional 50 sub-basins and the interpretation of the sedimentation patterns within the lake is thereby facilitated. 3.7. TERRESTRIAL MATERIALS Samples of terrestrial materials were collected in each lake basin. Soils on different substrates were sub-sampled within visible horizons. Bedrock and poorly-sorted unconsolidated sediments from exposed outcrops, river or gully bank materials, were also obtained from different areas within each lake basin. An attempt was made to gather rock specimens from all lithologies present in the basin. Bedrock samples were cut using a diamond-head drill and gravity driven saw, while surficial terrestrial sediments were dried, disaggregated, sieved to isolate the <2 mm size fraction and bottled into small sample cylinders. These materials were analysed for magnetic susceptibility and SIRM. The techniques used to establish the magnetic properties of lake sediments were applied to establish the same parameters for all terrestrial sediment and bedrock specimens. Some bedrock specimens as well as some sediment samples which were particularly coarse in texture were not suitable for magnetic analysis. This factor in addition to limited accessibility of some of the study areas has resulted in a spatial clustering of sampling sites which may not reflect the range of materials available in the basins. Every effort, however, was made in the field to acquire a broad range of material types. 3.8. SHORELINE SURVEY Shoreline assessments consist of noting the type of vegetation (tree type, marsh, low vegetation, grasses), the predominant sediment size on beaches (sand, gravel, boulders), and the 51 presence of woody debris, snags, or rocky shores within 2 metres of the shoreline. These surveys were used to summarize shoreline characteristics of each lake. Typical assemblages of material and vegetation were identified. Chapter 4 The Study Areas 52 4.1. G E N E R A L PHYSICAL SETTING The drainage basins of the four lakes under study are found in the Vancouver Island Mountains physiographic region , immediately north east of the Estevan Coastal Plain located on the west coast of Vancouver Island, British Columbia, near Clayoquot and Barkley Sounds (Fig. 4.1). 4.1.1. Geology The Wrangellia terrane which forms the basement of the field areas consists of three thick volcanic-sedimentary sequences: the Paleozoic Sicker Group, the Upper Triassic Vancouver Group, and the lower Jurassic Bonanza Group (Massey, 1992). The Sicker and Vancouver Groups are commonly intruded by batholiths of the Island Intrusions (Muller and Carson, 1969). Most of the study region is underlain by two major rock units: the Middle to Upper Triassic Karmutsen Formation of the Vancouver Group and the Jurassic Island Plutonic Suite (Massey, 1994). The Karmutsen Formation consists of basaltic and andesitic pillow lavas, pillow breccias, flows and tuffs, whereas the Island Plutonic Suite is made up of granodiorite, quartz diorite, and quartz monzonite. The area is cut by steep major northwest-southeast trending faults, roughly parallel to the coast (Muller and Carson, 1969). The Maggie Lake watershed is geologically the most complex of the four study basins (Fig. 4.2). The area is mainly underlain by the Early Jurassic Island Plutonic Suite. Outcrops of undivided volcanics of the Lower Jurassic Bonanza Group, limestones of the Triassic Quatsino Formation, Tertiary Clayoquot Intrusive Suite, and sandstone conglomerate are found in several 53 Fig 4 .1 : Locat ion of the study area. Dotted l ines refer to watershed boundar ies and bold text to study lake names . Kite Lake watershed ^ ^ E \ / Handsome x / ^ ^ I Mountain Lucky 1 Mountain! J S 2 \s Kitefc££ Lake^~1 — — — T ' * " ) ^ \ . ) \ \ i / ^ B l a c k Peak geological boundary fault 1 Karmutsen Formation 2 Island Plutonic Suite 3 Bonanza Group 4 Granitic Intrusions 5 Quatsino Formation 6 Sicker Group 7 Clayoquot Intrusive Suite 8 Sandstone Conglomerate 0 1 2 3 km 54 Cats Ears Peak Toquart Lake watershed f -^ 1 jW \ Tripple \ P e a k /CI *L 4 1 7 N X \ \ Mount/ V / - ^ " / H a l l 4 / ( J /\ 2 ^ Y 2 I 7 % 1 J \ / 1 ;>^v « 2 l | l Toquart Lake Clayoquot Lake watershed / A 1 / ) i / >» \ / N A*" "V I 3 ( 1 1 3 ^ { 1 j f t ^ y Y / I 1 1 \ t" \ y i s y ^ 1 I 6 J ' ClayoquoFX_^ \ / 1 / Hidden Peak Figure 4.2.: Bedrock geology of the four study watersheds (Muller, 1968; Massey , 1994). 55 areas of the basin. The watershed of Toquart lake is mostly underlain by Jurassic granitic intrusions and the Karmutsen Formation; the Island Plutonic Suite is found around the lake (Fig. 4.2). Upper reaches of the Kite Lake watershed are underlain by the Karmutsen formation, while lower reaches of the two contributing valleys are underlain by the Island Plutonic Suite (Fig. 4.2). Approximately 80% of the catchment of Clayoquot Lake is underlain by the Karmutsen Formation (Fritz, 1996); in the southwest corner of the basin, Paleozoic bedrock of the Sicker Group (composed of basalt to rhyolite volcanic tuff, breccia and argillite) is exposed (Fig. 4.2). Small pockets of Bonanza Group and Quatsino Formation can be found in the upper reaches of the catchment. Surficial materials of the study areas are dominated by colluvium and Pleistocene glacial deposits. Colluvium is particularly extensive at the base of steep slopes in the upper reaches of Clayoquot and Toquart watersheds (Fritz, 1996; Hudson, 1994). Glacial deposits consist of till and glaciofluvial sediments of various thicknesses (Fig. 4.3). In general, till is thickest and most extensive in the catchment of Maggie Lake, relatively common and relatively thick in the Toquart watershed, and much more patchy and thin in the Kite and Clayoquot watersheds. Fluvial deposits comprise the floodplains of the major contributing creeks. Soils are predominantly Ferro-Humic Podzols developed on poorly-sorted colluvial and glacial deposits (Massey, 1994). Podzolic Bhf horizons are enriched in organic carbon, iron and aluminum (Valentine etal., 1978). In contrast to the other study basins, soils of Clayoquot valley are predominantly folisols, formed where forest litter accumulates directly over the colluvium or bedrock (Fritz, 1996). Figure 4.3: Surficial materials in the study region: a) Maggie Lake watershed, b)Toquart Lake watershed (hammer for scale). 57 4.1.2. Climate and Hydrology The climate of the study region is influenced by its proximity to the Pacific Ocean and its mountainous topography. Temperatures are mild in the winter and cool in the summer (Clayoquot Sound Scientific Panel, 1995), although maritime influence becomes less significant with increasing distance from the outer coast. Most precipitation data available in the region are collected along the Estevan Coastal Plain, and may not be representative of the study basins. Annual precipitation averages 2977 mm at Tofino (36 year record between 1943 and 1990) and 3374 mm (years of record: 1957-1997) at the Ucluelet-Kennedy camp station near Ucluelet (see Appendix A). Precipitation occurs primarily during winter months, with mean monthly precipitation from November through January of 400-500 mm (Fig. 4.4). Extreme daily precipitation can reach 180-220 mm in winter and 50-135 mm in summer (Clayoquot Sound Scientific Panel, 1995). The nature of winter storms coming from the Pacific Ocean and the rapid change in relief in the coastal zone lead to spatially variable rainfall patterns. Precipitation data available from Clayoquot Lake (Clayoquot Biosphere Project, 1996, in Fritz, 1996) show that precipitation in Clayoquot valley in October 1995 was twice as much as that reported at the Ucluelet-Kennedy camp station. Over 7500 mm of precipitation was reported at the Brynnor Mine in the Maggie Lake watershed from October 1960 to September 1961 (Mines and Petroleum Resources Report, 1961). Further evidence is provided in the Toquart watershed where annual rainfall was reported at three stations (Table 4.1). These figures are again much higher than those of the Estevan Coastal Plain stations showing the local influence of Barkley Sound and the Mackenzie Range (Fig. 4.1; Appendix A). There is no stream gauging station in any study basin. Therefore, specific hydrological Figure 4.4: Mean monthly temperature and precipitation in the study region. Period of record (yrs): Tofino 48, Ucluelet Kennedy camp 26, Estevan Point 83, Carnation Creek 20, Port Alberni 30 (Clayoquot Sound Scientific Panel, 1995). data are non-existent and observations are limited. Despite interception by vegetation, heavy precipitation in forested basins of coastal British Columbia results in a quick stream discharge response due to well-established sub-surface pathways (Chamberlain, 1972). Flashy discharge is also a function of the weather. It has been reported as a common phenomenon for Toquart and Clayoquot rivers (Ministry of Forests, 1993; Waddington, 1994). The predominance of rocky ground is an additional factor in Clayoquot valley. Low baseflow during summer months is common, with many headwater streams being dry throughout the summer (Karen Halwas, pers.comm., 1996) Table 4.1. Precipitation pattern from the coast to the headwaters of the Toquart Valley (Ministry of Forests, 1993). Annual rainfall (mm) Mouth of the Toquart River 4500-5000 Toquart Lake 5500-6350 Head of the Toquart River valley 6350-7600 Note: Period of record is unknown though the station appears to have been established in the early seventies and is no longer being operated. 4.2. M A G G I E L A K E WATERSHED 4.2.1. Geomorphology and Drainage Network The drainage basin of Maggie Lake is located between Kennedy Lake and the shores of Barkley Sound (Fig. 4.1). Its general characteristics are summarized in Table 4.2. Closest to the coast, it is characterized by low to medium relief with four high points: Draw Mountain, Mount Dawley, Frederick Mountain and Mount Redford (Fig. 4.5, 4.6). With an overall elevation range of 850 m, 400-600 m of relief between ridge and valley floors is common. Slopes vary generally Figure 4.5 relief. Maggie Lake and its watershed Note mine waste area in the foreground and general Figure 4.6: Forestry activity in the Magg ie Lake watershed. 62 between 10 and 40% grade, with the steepest gradients of 50 to 80% beneath Draw Mountain and Mt. Redford. Thick till mantles the bottom of the valleys, while some bedrock outcrops can be seen on the upper part of slopes where less till has accumulated. The lower reach of Draw Creek has a well-developed floodplain but a relatively small delta protruding into the lake. In contrast, the floodplain of Paradise Creek broadens in the last kilometre above the lake to form an extensive delta. Below the lake outflow, Maggie River flows over 1.8 km down to the Macoah Passage of Barkley Sound. An important consideration for sediment yield studies is the significance of upstream lakes acting as sediment traps. Of the four other lakes in the Maggie Lake watershed, three are not likely to trap significant amounts of sediments due to their far upstream location within the drainage network. An old iron-ore quarry which has become a lake near the mine waste is also not a likely sediment trap (Fig. 4.6). Table 4.2. Summary of catchment characteristics. Maggie Toquart Kite Clayoquot Drainage area (km2) 57 68 25 67 Catchment: lake ratio 26 68 125 134 Range of relief (m) 50-900 69-1559 120-1300 0-1465 Drainage density (km-km"2) 0.79 1.01 0.81 1.03 Logged area (%) 87 7 12 Roads (km) 95 16 12 Road density (knvkm"2) 1.68 0.24 0.57 Period of logging 1956-1993 1981-1994 1991-1996 63 4.2.2. Disturbance History Due to the nature of the McMillan Bloedel forest cover maps, dates of stand establishment following logging, rather than date of harvesting, had to be used to reconstruct the timber harvesting history in the Maggie Lake watershed. Logging began in the early 1950's, although one stand was established as early as 1939. Eighty seven percent of the watershed has been harvested over the last forty years (Fig. 4.6). Heavy harvesting periods occurred in the early sixties and early eighties, while the seventies also saw a large number of cut blocks harvested. Logging activities have been limited since the early 1990s, although road deactivation and stream rehabilitation are still being carried out. Gravel roads total 95 km; while they are classified as active, most are not maintained (Fig. 4.6). Three groups use the main Toquart Bay road which crosses the Maggie watershed: logging companies harvesting nearby watersheds, native communities, and tourists to Toquart Bay. Approximately 49, 000 people used the Toquart Bay Forest Service campsite in 1991 (Ministry of Forests, 1993). While this is an annual figure, the site is mostly used between June and September by fishermen and kayakers who frequent the Toquart Bay and Broken Island Group recreational areas (Fig. 4.1). Several slope failures are visible on 1988 and 1994 air photos in the northeast section of the drainage north of Redford Creek, as well as immediately above the eastern shoreline of the lake (see Fig. 4.6 and 4.7). Other areas affected by mass movements include the area between Mount Dawley and Mount Frederick. Many of these failures initiated in sidecast material of mid-slope roads. The mine waste pile located south of the old quarry and adjacent to Draw Creek accumulated during the period of operation of the Brynnor (Braynor) Mine (Fig. 4.5, 4.6; Ministry of Forests, 1993). Magnetite was extracted over a period of eight years between 1962-Figure 4.7: The disturbed eastern shoreline of Maggie Lake, showing evidence of mass movement activity along Gully 1, Gully 2, and Gully 3 from left to right. Bridge crossing Gully 3 for scale. 65 1969. A crushing plant was established next to the open mine while the facility to produce iron concentrates for export was located outside of the watershed near the Toquart Bay campsite (Mines and Petroleum Resources Report, 1961). 4 . 3 . T O Q U A R T L A K E WATERSHED 4 . 3 . 1 . Geomorphology and Drainage Network The Toquart watershed is located approximately 24 km from Ucluelet, north of Toquart Bay, and is characterized by a range of relief of 1500 m (see Table 4.2 for summary of characteristics). Triple Peak and Cats Ears Peak of the Mackenzie Range delineate the northern most limit of the basin (Fig. 4.8, and 4.9). Steep slopes (approximately 60-75% gradient) occupy most of the basin, with the exception of a small area to the west of the lake where gentler slopes on the order of 15% exist. Two u-shaped valleys occupy the northern half of the drainage basin (Fig. 4.9 and 4.10). The western headwater valley trends along a fault. Steep cliffs are common along the back walls of the valley. A relatively thin mantle of till covers the hillslopes with occasional outcrops of bedrock. The lower third of Toquart River flows over a broad floodplain, splitting into two channels in the last kilometre above the lake. Several steep gullies drain the eastern slopes adjacent to the lake. The Toquart River delta extends out into the lake, thereby creating bays on either side of it. Toquart River drains into Toquart Bay 4.5 km from the lake outflow. 4 . 3 . 2 . Disturbance History Logging in the catchment of Toquart Lake began in the mid to late eighties. Its extent is 66 Figure 4.8: Toquart Lake with Triple Peak and Cats Ears Peak in the background relief and clearcut next to shoreline. Note range of Figure 4.9: The Toquart Lake Watershed showing location of natural and forestry related disturbance. Figure 4.10: Eastern headwater valley, Toquart Lake watershed. Note bedrock failures in the background. 69 quite limited, covering approximately 7% of the drainage area (Fig. 4.9). The main road was extended from the Lower Toquart valley beyond the lake in 1983, and now continues into the eastern tributary of the upper basin, covering a total of 16 km. No roads have been constructed on the west side of the river, although future development plans include two bridges crossing the Toquart River above the lake (pers.comm. Mike Greig, 1997). In terms of natural disturbance, several rock slides are visible on the head walls of the eastern headwater valley (Fig. 4.10). Several slope failures located in the tributary valleys of the upper Toquart River are visible on 1989 air photos. Debris flow fans at the mouth of tributary valleys are common (Hudson, 1994; Fig. 4.9). A colluvial fan is discernible on the southeast shores of the lower basin of Toquart Lake (Fig 4.11). 4.4. K I T E L A K E WATERSHED 4.4.1. Geomorphology and Drainage Network Kite Lake drainage basin is located northeast of Toquart Bay (Table 4.2 for summary of characteristics). It is characterized by local relief of 600-800 m and gradients of 30-50%, with the exception of the steeper slopes (65-80% gradient) below Handsome Mountain (1360 m elevation) and Lucky Mountain (1250 m elevation). Till occurs in topographic lows, while bedrock outcrops are common on hillslopes. Talus slopes exist immediately below Lucky Mountain cliffs. Lucky Creek drains the northern part of the drainage basin, while the other major creek contributing to Kite Lake trends east-west along a major fault (Fig. 4.2), occupying the eastern portion of the basin (Fig. 4.12). Valleys associated with the two creeks are u-shaped and are divided by a long oblong bedrock high (680 m). The eastern shoreline of Kite Lake is Figure 4.11: Colluvial fan on the southeast shore of Toquart Lake's lower basin. Figure 4.12: The Kite Lake watershed showing location of natural and forestry-related disturbance. 72 entirely composed of deltaic deposits from these two creeks. Two lakes occupy the headwaters of Lucky Creek. The larger of the two (37 ha) drains approximately one third of the Kite Lake watershed. This upper portion of the basin is separated from the lower portion by an east-trending ridge. The substantial size of the larger lake and the area that it drains warrants consideration of its role as an upstream sediment trap. The lower part of Lucky Creek drains 5 km from the Kite Lake outflow, through Ellswick lake and down to Toquart Bay. The Kite lake watershed is sheltered from the coast by a west-northwest trending ridge. 4.4.2. Disturbance History Logging activity in the Kite Lake watershed is the most recent of the three basins, having begun in 1990 (Fig.4.12). Twelve percent of the drainage area has been logged in this short time span. Roads extend along both contributing creeks and cover approximately 12 km. Clear-cut harvesting is extensive along half of the lake's shoreline, thus directly influencing the lake (Fig. 4.13). Assessment of natural disturbance is limited to examination of 1989 air photos: two failures were identified on the south slopes of Lucky Mountain, and four on the south-facing slopes above Lucky Creek (Fig. 4.12). 4.5. C L A Y O Q U O T L A K E WATERSHED 4.5.1. Geomorphology and Drainage Network Located north east of the Clayoquot Arm of Kennedy Lake, Clayoquot basin's U-shaped valley is surrounded by steep terrain which is cut by v-shaped tributaries (Fig. 4.14). Most peaks in the area are unnamed and tower over 1000 m in elevation above Clayoquot River (Table 4.2 73 Figure 4.13: Disturbance related to forestry activity: a) overview of Kite Lake and clearcut of 1992, b) the effect of windthrow on buffer and lake shoreline. Figure 4.14: The Clayoquot Lake watershed showing location of landsl ides (Fritz, 1996). 75 for summary of characteristics). Located in the southeastern corner of the basin in the Maitland Range, Hidden Peak reaches 1465 m above sea level. The eastern side of the basin is otherwise less steep (50-70%) than the western side of the valley where gradients of 65-80% are common. Local relief of 800 m and cliffs are very common in this basin, as are talus slopes. Limited glaciofluvial and till deposits are found at the mouths of two tributaries (Waddington, 1994). Upper slopes are covered in colluvial material, while the valley floor is covered by thick accumulations of forest litter. The lower third of Clayoquot River flows over a well-developed floodplain. Clayoquot River delta deposits extend well into the lake, creating two sheltered bays similar to those found in Toquart Lake (Fig. 4.14). Most of its tributaries flow along northwest-southeast trending faults. Aside from Clayoquot River, the lake has two inflowing streams along its western shores. One of these is a fourth-order stream with an extensive fan made up of deltaic deposits from the creek and colluvial materials from a much bigger colluvial fan (Fig. 4.14). Accumulation of debris at the mouths of these two tributaries may have caused the impoundment of Clayoquot Lake (Fritz, 1997 pers comm). Partly filled in by an extensive marshland, Norgar Lake acts as a sediment trap along the Clayoquot River, below three much smaller lakes (Fig. 4.14). There are several small and relatively insignificant lakes and cirques in the headwaters of some of the tributaries. 4.5.2. Disturbance History It is necessary to establish a chronology of disturbance in Clayoquot Lake watershed to provide an understanding of the local controls on the lake sediment record and the extent to which this may differ from the lacustrine record of the logged watersheds. Two studies of natural 76 disturbance have been carried out. A landslide inventory which distinguished between rockslides, rockfalls, debris flows and debris avalanches, showed that rock slides were the most common mass movement events in the area, followed by mixed debris flow/debris avalanches (Fritz, 1996). Pearson (1995) reported similar results in her assessment of landslides in the valley. Clayoquot River shows very little change in its channel configuration between 1939 and 1988 except for one minor channel shift which may be associated with the 1946 earthquake (Pearson, 1995). The chronological and spatial distribution of landslides is important in explaining the nature of their impact on the lacustrine record. Perhaps the most obvious feature of disturbance is the 1995 landslide immediately above Clayoquot Lake (Fig. 4.15). Initiated as a rock slide, it blocked a creek and developed into a debris flow, entering the lake on the western shore north of the narrows. Thirty two percent of all landslides reported in the study did not reach streams (Fritz, 1996). While this may affect the magnitude of the downstream sediment yield response, muddy waters draining these landslides most likely contributed to the downstream transfer of fine sediments. The majority of the landslides that are visible on air photos occurred on the west side of Clayoquot River and around Norgar Lake (Fig. 4.14). Fritz (1996) showed that 53% of landslides occurred prior to 1939, while most of the remainder occurred between 1939 and 1954 (Table 4.3). The majority of landslides which occurred prior to 1939 initiated on the headwalls of the western tributary valleys below Norgar Lake. Of the 37 landslides which occurred between 1939 and 1954, four were located immediately above Clayoquot Lake in the vicinity of the 1995 slide. Based on the number of slides which occurred over such a short period of time, there is bound to have been an effect on the local sediment cascade, although those above Norgar Lake are unlikely to have had an effect on the sediment record of Clayoquot Lake. Nine Figure 4.15: Landslide above Clayoquot Lake (October, 1995). 78 of twelve landslides which occurred between 1988 and 1994 initiated in the west tributary above Clayoquot lake. None of them however reached the nearby stream. This is once again a very high value for a six year period. As many happened in the same area, it is possible that Fritz (1996) identified parts of one major failure as individual failures. Table 4.3: Frequency of landslides in Clayoquot valley (Fritz, 1996). Period frequency of landslides Prior to 1939 59 1939-1957 37 1957-1970 1 1970-1981 0 1981-1988 1 1988-1994 12 After 1994 1 The effect of these landslides on the lacustrine sediment record remains unknown. While the connection between hillslope and drainage is critical in determining transfer of larger particles, mobilization of finer particles is unlikely to be affected by the position of the landslide in relation to the creek and more likely to be controlled by local generation of surface runoff. 4.6. C H A R A C T E R I S T I C S O F T H E S T U D Y L A K E S Knowing the bottom morphology provides a greater understanding of the sedimentation patterns within the lake. Lake shoreline surveys provide information regarding potential for lake shore erosion to contribute to the overall lacustrine sediment accumulation. These two aspects are described briefly for each lake. 79 4.6.1. Maggie Lake Maggie Lake is an elongate lake divided into an upper basin with maximum depth of 39 m and a lower basin with maximum depth of 45 m (Fig. 4.16). Morphometry of the upper basin is characterized by moderately steep sides (30% gradient) and a smooth to slightly undulating bottom. Graphical outputs of the bathymetric soundings reveal evidence of slumping at the base of the lake side-walls (Fig. 4.17). The lower basin exhibits similar gradients but a more complex bottom morphology. Two bedrock highs are visible in the lower third of the lake and the basin is slightly asymmetrical with maximum depths along the eastern shoreline (Fig. 4.16). The bottom topography is otherwise smooth to slightly irregular with evidence of slumping limited to the area around the Paradise Creek delta (Fig. 4.17). The upper basin of Maggie Lake is characterized by low angle gravel shores with low vegetation or marsh. This kind of shore is less dominant in the lower lake basin: the northeast shore is covered in dense forest with occasional gravel fans from gullies on adjacent slopes, while the southwest shore is characterized by bedrock headlands and low vegetation (including marshes) in sheltered bays. Gravel or bouldery beaches in sheltered bays are commonly strewn with woody debris. The apparent sources of sediments are from the banks of inflowing creeks and gullies on the slopes above the northeast shores of the lower basin, and the Toquart Bay road (Fig. 4.16, and 4.7). Lake shore erosion by wave action during prolonged windy conditions may be significant due to the available fetch (longest-3.5 km). However, loose sediment sources are limited within the immediate shorelines. 80 Draw Creek MAGGIE LAKE 0 250 500 750 Paradise Creek fig boat launch • fish hatchery — Toquart Bay Rd. • gravel fans • logged m/g/v/w b/g/wN g/b/v/wT Figure 4.16: Magg ie Lake : a) Bathymetr ic map showing echo sounder transects and coring locations; b) map showing shorel ine features. F a n s not drawn to sca le . The majority of the shores were logged within the last 20 to 30 years . 81 o O J CM LT3 CD E o " r a CD ' c J= Q. CD Q CM T— CD m ra o CD C CO CD C CD ra co i = CD .2 o ra o 2 o ™ **— tn D) r- £ ' I Li. CO CD "ft CO CD O CD C CD TO "D — ' > CD LU O) . ro co E x : o o j= ra co <•>• •c CO ° CO £ 0) C "raff § ^ 6 CO O CD N _ O "C * -JC O C o x : o W~ CD CD " O O 3 CD CD 82 4.6.2. Toquart Lake Little difference in maximum depths are encountered in the two sub-basins of Toquart Lake (see Fig. 4.18). Morphometry of the Toquart upper basin is relatively simple with 40% gradients along side walls and smooth bottom topography. The bottom is irregular in the upper section of the lake immediately adjacent to the deltas of the two arms of the Toquart River (Fig. 4.19). A northwest-southeast trending ridge at the southwest end of the basin is of limited extent. The lower basin exhibits sidewalls with lower gradients (30%) and undulating bottom topography (Fig. 4.19). Evidence of slumping is limited to areas immediately below gullies or small creeks. The upper basin shoreline is dominated by bedrock with small coves of marsh and low vegetation (alders, brush and high grasses). A gravel delta protrudes into the southeast corner of the upper basin (Fig. 4.18). The lower basin is much less homogeneous. Cedars, Douglas firs and hemlock grow along the shoreline, while alders, marsh and low vegetation occur in some sections. Below the clear-cut, the shoreline is characterized by gravel fans from upslope gullies with some evidence of bank erosion at the base of one of the fans. The outflowing arm of the lake is characterized by marshes along its edges. Most of the shoreline can be characterized as stable with very limited fine sediment sources. 4.6.3. Kite Lake Kite Lake has a very simple bottom morphometry with 20% side slopes and a bowl shaped trough elongated in the east-west direction (Fig. 4.20). There is no evidence of slumping off the delta and lake-bottom topography is smooth (Fig. 4.21). The north shore is characterized by low vegetation (mostly alders, brush and high grasses), woody debris and gravelly to bouldery 83 TOQUART LAKE Toquart River I m/v m-marsh v-low vegetation b-boulder beach g-gravel beach t-forested r-bedrock w-woody debris l-logs alluvial fan gravel fans logged Toquart Rd. outflow Figure 4.18. Toquart Lake : a) bathymetric map showing echo sounder transects and coring locations; b) map showing shorel ine features. F a n s are not drawn to sca le . 84 Lucky Creek b/g r/l 9 | 9 r f \ t logging road m-marsh w-woody debris v-low vegetat ion l-logs/fallen trees 0 125 250 375 g-gravel beach b-boulder beach I 'I I" I I I , . . . | : » ^ ^ r -bed rock logged-1992 m t-fo r e s t e d gravel fan contour interval: 10 m Figure 4.20. Kite Lake : a) bathymetric map showing location of echo sounding transects and cores; b) map showing shorel ine features. Fans are not drawn to sca le . A A' 1:3510 Depth interval: 10 m Figure 4.21: E c h o sounder chart from Kite Lake. S e e Figure 4.20 for location of transect. 87 shorelines (Fig. 4.20). Timber harvesting and windthrow have left significant amounts of small woody debris, snags and fallen trees (Fig. 4.13). The east shore is characterized by two deltas which typically consists of gravel bars, marsh and low vegetation. The south shores are dominated by gravel beaches that are several metres wide and vegetated by poplar trees. Bedrock outcrops near the outlet. There are no fine sediment sources along the shoreline. 4.6.4. Clayoquot Lake The morphometry of Clayoquot lake is relatively complex. An extensive delta protrudes into a shallow, flat-floored upper basin (11m maximum depth) with channel-like features along the shorelines (Fig. 4.22). Gradients vary between 9 and 50%,with an average approximately at 30%. The lower basin is a much deeper typical bowl-shaped depression (45 m maximum depth) with the exception of a relict channel-like feature (7-8 m deep and 62 m wide) in the western corner of the lake (Fig. 4.23). Bottom topography is otherwise undulating with some evidence of slumping immediately below the deltas of the western shore (Fig. 4.6). The most distinct feature of the lake is the steep cliffs on the north east shore. Colluvium is ubiquitous with large blocks of bedrock coming from overhanging cliffs. Rocky shorelines of the upper basin of Clayoquot lake are very similar to those of upper Toquart Lake. Two shallow bays (<50 cm deep) on either side of the Clayoquot River delta are covered by marsh vegetation. Shorelines of the narrows consist predominantly of marsh vegetation with the exceptions of sandy gravel associated with an extensive debris flow fan on the west shore and rocky outcrops on the east shore (Fig. 4.22). The lower basin of Clayoquot Lake can be described by two shoreline types. On the northwest side are a series of colluvial and alluvial gravel fans (Fig. 4.22). Cedars otherwise Figure 4.22. Clayoquot Lake: a) bathymetric map showing echo sounder transects and coring locations; b) map showing shorel ine features. Fans are not drawn to sca le . 89 C C' 1: 5639 Depth interval: 10 m Figure 4.23: E c h o sounder chart from Clayoquot Lake 's lower bas in. S e e Figure 4.22. for location of transect. Note the subaqueous channel . 90 grow right to the shoreline and large woody debris is common. On the east side of the lower basin of the lake, a mixture of rocky shorelines, low vegetation and marsh make up a majority of the shoreline types encountered. Erosion of shores most likely occurs where marsh vegetation dominates and fine sediment accumulates. This is evident near the Clayoquot Biosphere Project (CBP) field station where lake levels rising several metres during severe winter storms have been observed. Sediment sources around Clayoquot Lake are limited to debris flow fans and deltas of inflowing creeks (Fig.4.22). 4.7. CATCHMENT COMPARISON AND SUMMARY The selection of comparable catchments is an essential part of this study's design (section 3.2). With this in mind, the degree of similarity and the differences between lakes are discussed in order to understand some of the variability encountered in the four lacustrine sediment records. All four lakes experience fluvially dominated sediment inputs, although mass movement is also a key process in the Clayoquot valley. Clayoquot, Toquart, and Maggie watersheds are similar in size and in the structure of their contributing drainage networks. Toquart Lake is particularly comparable to Clayoquot Lake in terms of the topography of contributing drainage basins, drainage network (density and structure) and lake morphology. All lakes are located within 50 km of each other and all three logged basins are approximately the same distance away from Barkley Sound (Fig. 4.1), thus providing control on climatic variability. There are some differences in degree of relief and surficial material cover present in the Maggie Lake watershed compared to the much steeper slopes with more exposed bedrock encountered in the other three basins. While Kite lake's drainage area is less than half of the others, its catchment to lake ratio remains comparable to the Clayoquot catchment to lake ratio 91 (Table 4.2). The catchment to lake ratio of Maggie Lake is relatively smaller than the other three basins. In terms of disturbance history, the three logged basins represent a variety of forestry impacts: the majority of the Maggie Lake watershed has been logged over a period of 40 years. Toquart's harvesting spans the last decade whereas Kite's harvesting history spans the last five years. While the Maggie Lake watershed has been logged on the order of 90%, Toquart Lake and Kite Lake watersheds have both been harvested on the order of 10%. Rock slides, rockfalls and debris flows are common mass movement processes in all four watersheds. The degree to which these are documented in existing reports varies. Thus a comparison of geomorphic activity across the four study basins is limited. Table 4.4 summarizes the characteristics of the four lakes under study. Maggie Lake is longest of the four study lakes exhibiting a typical oblong shape. While both are oriented in Table 4.4: Summary of lake characteristics. Maggie Toquart Kite Clayoquot Lake area (km2) 2.2 1.0 0.2 0-5 Maximum depth (m) 45 35 26 45 Lake volume (m3) 6.3 x 107 2.2 x 107 3.6 x 106 8.3 x 106* Residency time (days)f 89-447 28-138 11-53 12-58J Trap Efficiency (%) 88-95 75-91 56-84 56-84 Elevation of lake (m) 30 ± 69 ± <120 <20 UTM coordinates 10-221308 10-278398 10-327364 10-164523 "The lake volume of Clayoquot Lake includes only the lower basin. f Residency time based on discharge calculated using the method outlined in Church, 1997. JResidency time calculated using whole lake volume. -Note the upper basin of Toquart has an area of 0.4 km while the lower basin has an area of 0.6 km. Both have maximum depths of 35 m. 92 different directions, Toquart and Clayoquot lakes have similar shapes with a long narrow upper basin separated from a relatively bowl-shaped lower basin, and a well developed delta at the mouth of the inflowing river. Maggie Lake's bathymetry shows a distinct upper basin but in contrast to the other two lakes, there is no constriction between the upper and lower basin. Kite Lake has a linear upstream shoreline but is otherwise round, tapering at the outflow. The relatively small catchment to lake ratio, greater water residency time and trap efficiency of Maggie Lake will probably be a factor in accounting for differences in the sediment record of the four study lakes. Chapter 5 The Sediment Record 93 5.1. I N T R O D U C T I O N 5.1.1. Description of the Sediment Record This chapter presents the results of the analyses of the sediment record of the four study lakes. For each lake, general stratigraphy is described using changes in x-ray grey tones to give an overview. 'Grey tone' is used throughout to refer to the different shades in grey scale density found in x-radiographic prints. To optimize resolution of the variations in grey tones, and in contrast to the original x-ray images, prints used in illustrations here were not processed at the same exposure. In general the following relation exists between grey tones and sediment density: the darker the grey, the more dense the material and conversely, the lighter the grey, the less dense the material. Consequently, sand layers are black while organic layers are white. Visual examination of cores was limited to field descriptions through core barrels. Splitting the cores in half was avoided due to the high moisture content and the consequent potential of altering the stratigraphy. The poor correspondence between field descriptions and the much more revealing x-radiographic images is attributed to smearing on the outer edge of the cores. Notes made in the field are therefore largely omitted. Sedimentary zones were defined using x-ray grey tone, organic content and magnetic susceptibility of all cores. Zones exhibit either uniform properties or internally consistent trends. Marker layers which occur within zones and which may be traced in other cores are also noted. For the purpose of this study, marker layers are defined as discrete, sharply bounded, relatively thin layers which may record local or lake-wide sedimentation events. Cross-core variability is 94 outlined for each lake through the examination of properties which were analysed at a short sampling interval in all cores. Results from the analyses of representative cores are illustrated and discussed in the text using sedimentary zones as a framework. The reader is referred to Appendix B for all x-rays and to Appendices C to E for complete data sets of all sediment properties. The following comments should be kept in mind in reviewing the properties of each sediment record. Descriptions of trends are made starting at the base and working upward to the top of a zone. Unless otherwise stated, 'moisture' refers to both total residual and hygroscopic moisture. Both total residual moisture and hygroscopic moisture are generally closely related to organic content, whilst trends in bulk density are generally inversely related to those of organic content. Changes in geochemical element concentration evident for a number of elements are likely to reflect changes in depositional conditions. The level of confidence in the interpretation increases with the number of elements which show similar trends. The ratio SIRM/Xo is described in general terms for the whole period of deposition covered in the cores as its high degree of variability makes establishing patterns within zone difficult. In contrast to the other parameters which have been assessed on all cores, texture and sediment geochemistry are based on a subset of cores. The degree to which these are representative of lake-wide conditions remains unknown. However, it is supposed that if the core which has been analysed is representative for other parameters, then it is likely to be representative for texture and geochemical properties. Having described the sediment properties for each zone, catchment sediment yields are presented based on the chronology adopted for each lake and the zonal correlation of cores across each lake. Similarities and differences between the sediment record of the four lakes are discussed, outlining local and regional variability. The last section of the chapter documents the 95 magnetic properties of terrestrial materials in all four lake basins. 5.1.2. Chronological Control Assessment of the correspondence between the sediment record and the history of natural and forestry-related disturbance is one of the main objectives of the current study. Consequently, one of the critical results is to establish a chronology of sediment deposition. Two dating techniques have been used to this end. The results of 137Cs and 210Pb assays are discussed below to establish the degree of chronological control obtained from these two techniques. With the exception of core Ml 1, the maximum in , 37Cs activity nominally corresponding to 1963 occurs over a relatively broad interval in the master cores of each lake (Fig. 5.1). Errors associated with the measurement of the isotopic activity in the sample layers do not allow differentiation of the peak at a higher resolution (Appendix E). In contrast, the identification of the onset of the rise in the activity of 137Cs is relatively straightforward (Fig. 5.1 and Appendix E). Dates derived from the activity of 210Pb indicate that core M16 documents the longest record of sediment deposition in Maggie Lake with a basal date of 1860. Longer records of sediment deposition are found in Kite Lake and Toquart Lake (167 years). Close examination of the results reveals discrepancies between the two chronologies which must be investigated to assess the potential biases of either dating technique. The 1954 137Cs marker corresponds to an older 210Pb age in every core, except core T10 (Fig. 5.1). This pattern is also apparent in the 1963 markers of cores M5 and CI. The 1963 maximum in core K2 has a younger range of 2I0Pb ages covering the period 1966 - 1972. While the offset between the two chronologies is comparable in cores M5 and CI, no consistent trend in the magnitude of the r-- m co co T - r— O ) 0 ) O ) G) o> CO CO o> o> o> O J 0> O) O) T - o> r— m T - e o t o v n r o o m c N O h - m i - h - CM c o N r— r— s ( 0 ( 0 ( O i D ( D i n i o ^ ^ * ^ c o c o O) O) 0 > 0 > 0 > 0 > 0 > 0 > 0 > 0 > 0 > 0 > 0 ) 0 ) o> o> o> o> o O-c o o o-CM o o CM CM CO CO m i n N « O ) o oi ^ N CO Tj- i n CO S CO O ) CM _• _• _• . _ • _ • CM CM c o * m ID s c o o> o CM r N n ^ in J2 ir W O N <M CM CM CM CM t ^ t o c o a > m o r ^ c o o ) i o c M c o c o c o o o m c o r - ~ 0 ) 0 > h ~ ' ^ - o o c o o ) c n c o c o c o s s c o c o d m o m t * ^ n w r o o i c o c o O ) O ) G> O ) CD 0 ) 0 ) 0 ) O ) Q ) 0> O ) O) O) O) G> G> O ) 0 ) 0 CD 00 CO 00 o CM c o <* m CD s c o o> C M C O ^ U I C O S C O O I N T N CO CM c o it i n id s oo oi ^ N c O T t i n c d ^ e d c i d ^ S 0 . - * m ' t o • ^ T - 1 - T - T - T - T - T - C M < M C M CN C M S to C O O ) CO N CO CO CO CD TJ- T - O h - i - N i t M O i f CO CM o i o i o i c o c o c o N r~- r - c o c o c o t o m m M - c o CM o ) o > o > C 7 > o > o > o ) o o o ) 0 ) 0 ) o o > 0 ) 0 ) o i o ) ( 7 i a ) c n o> o o CO O T C M c O i n <D N c o o> r ' ' N n * i n ( p N I O C I I N ^ CM CO ^ C N c o T t i o ' c b s c o ' o J N r i * i r i i D N c d o ) 6 N 2 «ri ' - T - f - T - ^ - T - T - T - C M <M CM CN m o o X } ' ey ing i _ O ) C CD o _ C Q . H •es d L _ o iriso o iriso >» pa > E TJ o CO o c a se CO \_ CD -*-« CD CO x: T J -«—< •a >4— o o > "CD to CD c T J o O CD sz CN 1 n o ea c o C L co" o CD b o CO o CD CD x: CO CD _ l ' ' CD sz D) O ) CO > '-4—* •d CD o i _ o CO Cs CO Cs ea c E acl E en CO CD O E - Q »4— O iaxi o c to CD c CD CO > CD CO 2 OJ sz D_ to CO 'oT x: —^< CO cri x: c CD D) x: c D ) CD CO u_ Jc m (LUO) mdaa 97 E o Q. 03 Q C s - 1 3 7 activity (Bq/kg) 300 Lead-210 derived Alternative dates - core 12 for core 1997 1997 1997 1992 1995 1988 1983 1991 1979 1973 1986 1969 1965 1982 1960 1957 1978 1953 1952 1974 1948 1945 1970 1940 1933 1965 1928 1926 1959 1922 1912 1953 1907 1898 1947 1893 1880 1941 1876 1859 1933 1855 1830 1922 1826 1910 Figure 5.1 b): Profi le of C s - 1 3 7 activity for Toquart Lake , with lead-210 der ived dates for compar ison. T h e grey box highlights the 1963 max imum in C s activity, whi le the arrow points to the onset of the rise in activity cor responding to 1954. Alternative dates are given based on a different isotope concentrat ion in the top layer (see text for d iscuss ion) . 98 Figure 5.1c): Profi le of C s activity for Kite and Clayoquot lakes, with lead-210 der ived dates for compar ison. Blank intervals were not measured T h e grey box highlights the 1963 maximum in C s activity, whi le the arrow points to the onset of the rise in activity corresponding to 1954. 99 offset is apparent. 210Pb dates in core T10 reveal a very different chronology from that of the 137Cs markers: the 1963 maximum has a much younger corresponding 210Pb age of 1973-1992, while the 1954 marker corresponds to a 210Pb age of 1965 (Fig. 5.1b). Some of the contradictions may be explained by the downward mobility of 137Cs. This phenomenon has been documented in other lake sediments and is particularly common in soft water lakes (Pennington et al, 1973; Wise, 1980; Blais, et al., 1995; Crusius and Anderson, 1995). The mechanism for downward mobility is not well understood, although several have been suggested: chemical diffusion (Crusius and Anderson, 1995), and physical and biological reworking of sediments (Pennington et al., 1973). Based on the fact that it is defined by the onset of isotopic activity, identification of the 1954 marker is most tenuous in these circumstances (Pennington et al., 1973). The distinction between the first substantial peak in 137Cs, corresponding to 1959, and the maximum peak corresponding to 1963 is also obscured (although not as significantly) by downward mobility, leading to a much broader/flatter peak in isotopic activity. Biological reworking and physical reworking from sediment focusing are possible mechanisms for the observed I37Cs profiles. Physical reworking by wave action is unlikely as cores were all collected in deep waters. However, the extent of the downward mobility compared to the relatively high sediment accumulation rates encountered in the study lakes suggest that chemical diffusion played a significant role in altering the isotopic profile (pers.comm. J. Cornett, 1997). The lack of consistency in diffusion rate remains unexplained. Another problem with the 137Cs technique is the possible contribution of 137Cs from catchment derived sediments in addition to that of atmospheric fallout (Wise, 1980). Catchment soils accumulate 137Cs fallout over time. Isotope concentrations in excess of the expected fallout 100 levels can be attributed to catchment sources. This process has been invoked to explain the upper tail of the 1963 maximum and may be responsible for the discrepancy found in the 1963 marker of core K2. Discrepancies between the chronologies of core T10 cannot be explained by either of the above problems related to the analysis of 137Cs . As such, it provides an opportunity to assess the possible bias of the 210Pb chronology related to the uncertainties of that technique. Two main assumptions were made in the modelling of the 210Pb activity which may account for some of the discrepancies. First, the isotopic activity in the top layer of each core had to be estimated and in general was assumed to be equal to the value in the layer below. Another approach is to attempt to extrapolate the increase observed in the layers below. The 210Pb activity in the upper section of core T10 changes so rapidly that it is hard to judge which method of estimation is more appropriate (pers.comm. J. Cornett, 1997). Sensitivity analysis of data in core T10 reveals that the discrepancy with the 137Cs chronology would be reduced if the assumed value of the top section was twice that of the value in the layer below (Fig. 5.1b). The 1963 marker would have an equivalent 210Pb age of 1969-1988, while the 1954 marker would have an equivalent age of 1960. While the discrepancy is attenuated, the 137Cs markers still correspond to younger 210Pb dates. Upward mobility of the 1954 137Cs marker and downward mobility of 210Pb (Crusius and Anderson, 1995) are unlikely. Thus, the discrepancy remains unexplained. The second assumption which was made in the modelling of 210Pb concerns the definition of the bottom of the 210Pb profile. The supported fraction of the total 210Pb activity is assumed to be in equilibrium and therefore constant at all depths. The depth at which 210Pb activity no longer changes over time represents the bottom of the profile. Dates are derived from the profile of unsupported 210Pb activity which decreases downcore according to the decay rate of the isotope. 101 Unlike T10, cores in other lakes did not reach background levels of supported 210Pb activity. Background levels and depths at which these were reached had to be estimated based on values found in other lakes in the area. This introduces uncertainty into the 210Pb chronology. The bottom of the profile is particularly sensitive to this assumption. Ages of sedimentary zones identified in each lake were assigned based on the correspondence of the two chronologies, as well as the following principles. Lead-210 dates were preferred when downward mobility of 137Cs was apparent from correspondingly younger 210Pb dates. In addition, the flattening of the 1963 maximum (from downward mobility or from catchment derived influx of I37Cs ) was taken into account when assessing its correspondence with the 210Pb chronology. In addition to the comparison of the two isotope records, chronological control can be assessed by the consistency in the chronology of correlated sedimentary zones or marker layers. Final discussion on the limits and constraints imposed on the adopted chronology is deferred until after these are presented. 5.2. M A G G I E L A K E Seventeen cores (average length - 31 cm) were collected in Maggie Lake. Cores Ml and Ml 5 are relatively short compared to all other cores (19 and 23 cm). There is very little disturbance associated with coring as revealed by the horizontal nature of almost all layers visible on the x-ray images (Fig. 5.2, Appendix B). Some in-situ disturbance is obvious in M10 and the bottom of core M2. Disturbance from coring and extrusion is found in the middle section of core M14 and the top of core M8 (Appendix B). With the exception of core M10, which was 102 M5 M18 Figure 5.2: X - ray image of cores in Magg ie Lake showing variation in the general grey tone pattern across the lake (Fig. 4.16 for core locations). Arrow points to change from light grey to darker grey tone: a) upper bas in. Figure 5.2: X- ray image of cores in Magg ie Lake showing variation in the general grey tone pattern across the lake (Fig. 4.16 for core locations). Arrow points to change from light grey to darker grey tone: b) lower bas in. 104 excluded from further analyses, these disturbances are relatively minor and do not jeopardize the quality of the sediment record. 5.2.1. General Stratigraphy X-radiographic images revealed a consistent pattern of grey tones in Maggie Lake cores: the lower section of most cores is characterized by a lighter (less dense) grey image interrupted by a layer consisting of fine sand and/or macro-organic fragments. The upper section of the core is characterized by a darker (more dense) grey image interrupted by a varying number of distinct layers. Figure 5.2 demonstrates the various forms of this general pattern). Cores M5 and Ml 8 are located within 200 m of each other, while Ml 6, and M12 are located in the lower basin (see Fig. 4.16). Marker layers are predominantly minerogenic (sand size), or predominantly organic, or finely laminated, or a combination of any of these. Thicknesses of layers range between 1 mm and 1 cm. 5.2.2. Sediment Properties Sediments are composed mainly of gyttja with an average of 15 % organics (Table 5.1). Bulk density, based on dry weight per wet volume, ranges between 0.2 and 1.0 g cm'3. Total residual moisture is relatively high with an average value of 58 ±9%. In every core throughout the lake, a well defined peak interrupts the otherwise non varying trend in magnetic susceptibility. The profile of the SIRM/Xo ratio displays a general upcore increase, although some cores exhibit a non-varying trend in the lower section of the core. Fine silt is the most common particle size, although other size fractions are also well represented. 105 Table 5.1: Average values (± standard deviation) of sediment properties of Maggie cores and core M18. ALL MAGGIE CORES M18 Organic content (%LOI) 15 ±5.7 12 ±2.8 Bulk density (g cm"3) 0.65 ±0.17 0.69 ±0.16 Total residual moisture (%) 58 ±8.6 53 ±5.4 Hygroscopic moisture (%) 2.5 ±0.93 2.1 ±0.39 Magnetic susceptibility (xlO"6 m3 kg*1) 1.8 ± 0.71 2.19 ± 1.0 SIRM/Xo ratio (k Am"1) 13 ± 3.1 11 ± 1.2 For the more detailed description of sediment properties that follows, core Ml 8 is used to represent lake-wide patterns, while core Ml 2, discussed later, provides an example of a core which differs from this lake-wide pattern. The average values of the sediment properties of Ml 8 are comparable to those of other Maggie cores (Table 5.1). In addition, core Ml 8 is well correlated with the central core of the upper basin (core M5) which is least likely to have a disturbed record compared with cores located in the lower basin across from the dissected and unstable hillslope (see section 3.4.2, Figs. 4.7, 4.16). Core M12 was chosen as it is well correlated to the dated, and similarly disturbed, core Ml 1 (see section 3.4.2). Four zones were defined on the basis of x-ray grey tones, organic content, and magnetic susceptibility of all Maggie Lake cores (Appendix B and C). Beginning at the bottom of core M18 (Fig. 5.2a, 5.3), Zone M-A (16.5- 20.9 cm depth) is generally a light grey tone, and exhibits a characteristic upward decrease in organic content and moisture, and a corresponding increase in bulk density. Magnetic susceptibility remains constant throughout this zone. A distinct sand layer at 21.5 cm depth with low organic content, high bulk density, low moisture and stable to low magnetic susceptibility interrupts Zone M-A (Fig. 5.2, and Fig. 5.3). Material is predominantly silt with minor fractions of sand and clay. In terms of geochemical properties (Fig. 5.4), almost all 106 Figure 5.4: Geochem ica l stratigraphy of core M18 . Prec is ion is within 5 % for all e lements except for calc ium which has a precis ion value of 9% . L e a d concentrat ions fell be low detection level for most of the downcore profile. 108 elements follow similar upcore trends, with the exception of calcium and cadmium. All elements except for zinc exhibit a minimum in concentration which coincides with the peak in coarser minerogenic particles at 21.5 cm depth. In terms of cross-core variability, there are some exceptions to the pattern of Zone M-A found in core M18. Zone M-A was not recognized in cores Ml (Fig. 5.5.a) and M17 (Fig. 5.5b) as evident by their organic content trends (see also Appendices B and C). In addition, the discrete layer which occurs within this zone is not found in M9, Ml 1, M12 and M14, while it dominates the sediment properties of Zone M-A in upper basin cores (Fig. 5.5 and Appendix B). Organic content can also be relatively constant in the upper basin cores (Fig. 5.5). Zone M-B at 11-16.5 cm depth is characterized by an increase to maximum values of magnetic susceptibility and a corresponding, although sometime stratigraphically lower, maximum in bulk density, and minimum in organic content and moisture (Fig. 5.3). The organic content trend changes from the zone below to an increasing trend which continues to the top of the core. Likewise, bulk density exhibits higher values than in Zone M-A from this zone upwards. There is more clay, and coarse and medium silt in Zone M-B compared to concentrations observed in Zone M-A. Fine silt is lowest in this zone compared to those above and below. The elements Na, K, Al, Fe, Mn and Zn all show a low concentration in this zone, coinciding with low values in organic content and high values of magnetic susceptibility. Concentrations of Si, Mg, Cr, Cu and Ni increase upward and are not related to either property. Cadmium and calcium do not follow either trend, exhibiting a decreasing trend and a high concentration respectively. In terms of cross-core variability, the pronounced nature of the magnetic susceptibility peak shows that Zone 109 c CO CO a) •«-Q . 3 ri> CN CO c © c o u o "c CO (uio) ujdap (wo) ujdsp co tr-io 2 2 o 8 » CO o _ J c 0) d) • — r~ 0)±= g> co CO — ^ & .£ co — Q-c (1) o c Q . o o ° 7 o <a c ro JS E° CD ° £ o c > » c = 2 la * i CO w •c o CO Q-> o CO CD CO CD CL >-CO o 2 c o <?. o c C CO s« . . CO 10 2) •£ 8 O) o L L Z I l l M-B is present in all cores (Fig. 5.6). However, as evident by organic content profiles and the x-ray images, it is interrupted by organic rich layers in cores M4, M17 and M14 (Fig 5.4 and Appendices B and C). Zone M-C found between 4.4 and 11 cm depth is characterized by sediment properties which remain constant, with the exception of magnetic susceptibility which, in some cores, decreases and clay content which continues to increase (Fig 5.2). This zone is dark to mid-grey with a graded upper boundary which is hard to identify on some x-ray images. Geochemical concentrations of all elements except for calcium reach a maximum at the base of the zone and then decrease upward. In terms of cross-core variability, Zone M-C is missing in M7 (Fig 5.4, Appendix B). The non-varying profiles of sediment parameters of this zone in cores M4 and Ml 1 are offset by layers with higher (Ml 1) and lower (M4) organic content (Fig. 5.5). These are visually obvious on x-rays (Appendix B). The uppermost Zone M-D (0-4.4 cm depth), is dark to mid-grey and is characterized by a renewed increase in organic content and moisture (Fig 5.2). The relatively non-varying value of magnetic susceptibility found in this zone as well as Zone M-C is slightly higher than the non-varying value found in Zone M-A. While this pattern is evident in the upper basin cores, it is confounded by the occurrence of spikes in magnetic susceptibility associated with discrete layers in the lower basin cores. Element concentrations are either stable or decreasing, coinciding with increases in sand and fine silt as well as increasing organic content. In terms of cross-core variability, sediment properties of core M3 do not follow the general pattern established above. Zone M-D is not found in Ml 1, and is represented by only 1 or two points in cores Ml7, Ml4, M7, andM13 (Fig. 5.5). 112 CO LO in o CM CO CO r Q 1 O 1 * CQ < 1 in 2 2 l \ s 5 - •* •CO H 1 H — — h - H 1 • 1—'— CM - T — s E •> o T " 15 o. a> o (/> 3 CO C ca a m o in o m o r - CM CM CO (LUO) L|}d9p (LUO) ujdap c o d) 8 0 ) 0 CO .»-. c CO CO cu co a) co g 8 o O c o ^ . ^ > U) • TO Li. ^ 2. o i l co "—^ •o-i 2 ca S x: C D W o Q. c Q. o > =3 C o Q * Q. . . co O CD CD LO o CD ^ CD ra .5>« 2 U I £ 114 The sediment properties of core Ml 2 demonstrate how the general pattern can be offset by local variability (Figs. 5.2b, 5.7). Departure from the norm occurs in the upper three zones. The low in organic content characteristic of Zone M-B is asymmetrical, while total residual moisture and bulk density are not as closely related to organic content as they tend to be in other cores. The general pattern in grey tone is still evident although two organic layers are quite prominent in a much lighter grey Zone M-D. Trends in texture are quite different from those observed in core Ml 8. Particle size distribution is dominated by fluctuating fractions of fine silt with a maximum in Zone M-A and a minimum in Zone M-B. Medium silt decreases in Zone M-B, subsequently remaining low upcore. Very fine silt increases sharply in Zone M-B, remaining high in the upper two zones. Clay is relatively constant with a higher fraction found at the base of Zones M-A and M-B (Fig. 5.7). The geochemical analysis of core Ml 2 resulted in much more variable patterns. The following assemblages of elements show similar upcore trends: K, Fe, and Al; Cr, Mg and Ni; and Cu and Ca (Fig. 5.8). Element concentrations in Zone M-A are generally increasing upcore, with exceptions in Na, K, Zn , Fe and Mn. Concentrations of elements are highly variable in Zone M-B and Zone M-D. Lows in concentrations of heavy metals in Zone M-B coincide with low values of organic content suggesting these two properties are correlated. While Na and K increase in Zone M-C, all other major elements and heavy metal concentrations decrease. In addition to these variable trends, element and metal concentrations are usually higher in core Ml2 than in core Ml8. While there is poor correspondence between the geochemical properties of cores Ml 8 and Ml2, other sediment properties are relatively well correlated in the two cores, while lake-wide correlations are evident from trends in organic content and magnetic susceptibility (Fig. 5.5 and 115 Figure 5 .8 :Geochemica l stratigraphy of core M12 . Prec is ion is within 5 % for all e lements except for one replicate of N a and S i which have precis ion levels of 1 5 % and 1 0 % respectively. L e a d concentrat ions fell below detection levels. 117 5.6). Cross-core variability evident in x-ray images supports the variability encountered in organic content and magnetic susceptibility (Appendix B). In the upper basin, cores closest to the inflowing Draw Creek are difficult to correlate with one another and with those located towards the center of the basin. Cores located in line with gullies adjacent to the lower basin show more anomalous layers which do not match the lake wide pattern. Discrete layers which cannot be traced throughout the lake occur in the upper sections of cores M8, M9, Ml 1, Ml 2, and Ml 4 (Appendix B). Cores M3 and Ml 7 are composed of sediment of variable density as evident from the mottled nature of the grey tones (Appendix B). Core M13 has a simple grey tone stratigraphy compared to neighbouring cores (Ml 1, Ml 2, M8 and M9), although the general pattern outlined above is still apparent (Appendix B). Despite the local variability of sediment properties in some of the cores, the sedimentary zones are still identified in almost all cores, thus justifying their definition. 5.2.3. Sediment Chronology Considering downward mobility of 137Cs, there is relatively good correspondence between the 1963 137Cs marker and the 210Pb derived dates in all three cores (Fig. 5.1a). The correspondence between the dates of correlated sedimentary zones across the three cores provides a check on the 210Pb chronology (Fig. 5.1a). The basal dates of Zones M-D and M-C in cores M5 and Ml 6 are well correlated (± 2 years). Although the top of zone M-B is chronologically well correlated in M5 and Ml 6, the base of this zone is 13 years younger in M16 (1940 in M5 vs 1953 in core M16), reaching an even higher value for the base of Zone M-A (20-year difference). There is only 6 years difference between the base of Zone M-A in core Ml 6 and the base of the same zone in core Mi l . Thus, while there is good agreement between the upper 118 zones of cores M5 and Ml 6, chronological correlation of sedimentary zones decreases downcore. This is related to assumptions made in the modelling of the 2I0Pb chronology which increasingly affect the derived age downcore (pers comm., Jack Cornett, 1997). In general, there is poor agreement between the 210Pb ages of Ml l's sedimentary zones and those found in the other two cores. While there is a good correspondence between the two isotopic records in core Ml 1, the lack of agreement with the dates of the sedimentary zones in the other two cores is problematic. Dates were assigned to each sedimentation zone (Table 5.2) based on the following criteria. As evident from its location and its other sediment properties, core Ml 1 records a history of local disturbance. Stratigraphic anomalies make the modelling and interpretation of the measured 210Pb activity difficult (Rowan et al., 1995). Thus, of the three, core Ml 1 is probably the least representative core. Consequently, data from cores M5 and Ml 6 were used for the chronological control of lake-wide sedimentary zones. As the dates of the upper two zones were quite similar in cores M5 and Ml 6, an average was used. For the lower two zones, the dates of Ml 6 were selected as there is closer agreement with the 1954 137Cs marker. Table 5.2: Ages of sedimentary zones. See text for selection criteria. Zone Age M-D 1997-1979 M-C 1979-1961 M-B 1961-1953 M-A 1953-1943 119 5.2.4 Catchment Sediment Yield Based on trap efficiency estimates of 88-95%, catchment sediment yields range between 46 and 112 t/yr/km2 over the period of deposition recorded in the four zones (Table 5.3). Trap efficiencies for this lake are based on estimates of discharge of 1.6 to 8.1 mY1 (see Appendix F). The higher trap efficiency value results in an 8% decrease in sediment yield. Temporal variability in sediment yield is most significant between the periods of 1943-1953 and 1953-1961. Sediment yield in Zone M-B is 1.4 times higher than that observed in Zone M-A. In contrast, the two most recent zones show relative decreases in sediment yield compared to earlier zones. A sensitivity analysis is presented for different critical water depths which define the lacustrine sediment depositional area used in the sediment yield calculation. A more conservative area of deposition (20m depth) leads to sediment yields 17 to 21% lower than the ones reported above (Table 5.3). Sediment yields quoted throughout this chapter are based on the 10 m critical depth. 5.3. T O Q U A R T L A K E Eleven cores (average length of 23 cm) were collected from Toquart Lake. In general, lower basin cores are longer, while upper basin cores are as short as 14 cm. Core disturbance from coring and extrusion is limited to the side walls of cores T3, T4 and T9 (Appendix B). Core T5 shows evidence of in-situ disturbance and was therefore not analyzed further (Appendix B). Otherwise, core disturbances are relatively minor and do not jeopardize the quality of the sediment record. 120 Table 5.3: Sediment yield for Maggie Lake catchment. Minimum and maximum values are based Zone Date Min. Yield-10 Max. Yield-10 Change from change ft/vr/km^ ft/vr/km** zone below* from M-A* M-D 1997-1979 46 50 0.67 0.61 M-C 1979-1961 69 75 0.67 0.92 M-B 1961-1953 103 112 1.4 1.4 M-A 1953-1943 76 82 Zone Date Min. Yield-20 Max. Yield-20 Change from change ft/vr/km2) (T/vr/km2>> zone below* from M-A* M-D 1997-1979 38 41 0.66 0.63 M-C 1979-1961 57 62 0.67 0.96 M-B 1961-1953 85 92 1.4 1.4 M-A 1953-1943 60 65 *Factor by which yield changes from previous zone or compared to Zone M-A. -Estimates of sediment yield were calculated assuming deposition over an area delimited by the 10 m contour and over an area delimited by the 20 m depth contour. -Sediment yield calculation data is in Appendix G. 5.3.1. General Stratigraphy The general stratigraphy of Toquart Lake is characterized by a change in grey tone in the upper 5 cm of the cores taking on various forms with some or all of the following properties: a darker grey tone, a less homogenous grey tone reflecting small fragments of variable densities, and laminations on the order of 1mm to 1cm of sand and/or organic debris (see Figure 5.9; Appendix B). In term of cross-core variability, the two cores closest to the lake's inflowing stream (T4 and T5) do not follow this general pattern and are crudely laminated with highly contrasted densities (Appendix B). Core T10 exhibits many abrupt changes in sediment density with laminations varying in size from 2 mm to 2 cm (Appendix B). 5.3.2. Sediment Properties Toquart cores are composed of gyttja and fine silt with typical bulk densities of 0.43 to 121 Figure 5.9: X-ray image of Toquart Lake cores showing variat ions in the general grey tone pattern across the lake (See F ig . 4.18 for core locations). 122 0.61 g cm'3. Organic content averages 20% and never exceeds 30%. Total residual moisture averages 65%, while magnetic susceptibility is between 0.89 and 1.44 xlO"6 m3 kg"1 (Table 5.4). All major elements and heavy metals conform to the same downcore profile except for the uppermost values of sodium and potassium. Core T9 was selected as a representative core as it resembles the dated core T10 and appeared to have the longest record of sediment deposition. In addition, as shown by data in Table 5.4, average values of sediment properties are similar to the average values of all Toquart cores. Toquart cores are divided into four zones defined by organic content, grey tone and magnetic susceptibility. Zone T-A is found in cores T2 and T7 (see Fig. 5.9) and is distinguished by its dark to mid-grey tone, and a bulk density that is greater than that found in the zone directly above. Organic and moisture contents are either increasing (core T7) or exhibiting a low (core T2) in this zone, while magnetic susceptibility increases. As Zone T-A does not appear in core T9, comments cannot be made on the texture or sediment geochemistry of this zone. Table 5.4: Average values (± standard deviation) of sediment properties of Toquart cores and core T9. ALL TOQUART CORES T9 Organic content (%LOI) 20 ±3.0 22 ± 2.7 Bulk density (g cm"3) 0.52 ±0.09 0.46 ±0.14 Total residual moisture (%) 65 ± 3.1 66 ±3.0 Hygroscopic moisture (%) 3.1 ±.55 3.4 ±0.40 Magnetic susceptibility (xlO"6 m3 kg"1) 1.3 ±0.14 0.93 ±0.11 SIRM/Xo ratio (k Am"1) 23 ±3.5 21 ±2.7 In core T9, Zone T-B (top at 9.9 cm depth) is characterized by a homogeneous mid-grey tone, decreasing to non-varying organic content, and increasing to non-varying magnetic 123 susceptibility and bulk density (Fig. 5.10). Over 75% of the minerogenic sediment is medium and fine silt (Fig. 5.10). Fractions of coarse silt are relatively non-varying throughout, except for two decreases occurring at approximately 13 and 18 cm depths (Fig.5.10). All elements except for sodium, potassium and copper show a minimum followed by a maximum in concentration (Fig. 5.11). The SIRM/Xo ratio is generally increasing to stable throughout this zone. In terms of cross-core variability, laminations of various grey tones interrupt this pattern in core T10, while the zone is absent in core T4. While upper basin cores show non-varying organic content and increasing magnetic susceptibility, the lower basin cores exhibit decreasing organic content and relatively non-varying magnetic susceptibility (Fig. 5.12, 5.13). The layer of lighter grey tone at the base of core T9 is correlated to a similar layer in core T10 (Appendix B). However, this marker layer is not found in other cores, and in particular in the older sediment record of cores T2 and T7 (Fig. 5.12, Appendix B). Zone T-C (5.5-9.9 cm depth) is characterized by a pronounced maximum in organic content, a minimum in density, a textured light to mid-grey tone, and very slight increases in sand, and clay particle sizes (Fig. 5.10). The dominance of fine and medium silt is maintained throughout this zone (Fig. 5.10). All geochemical elements show a minimum in concentration (Fig. 5.11). The SIRM/Xo ratio increases throughout this stratigraphic unit as well as throughout the zone above. In terms of cross-core variability, magnetic susceptibility increases in upper basin cores, in contrast to the well-defined minimum in lower basin cores (Fig. 5.13). The uppermost Zone T-D, from 0 to 5.5 cm depth, is characterized by a minimum in organic content, a high in magnetic susceptibility, a dark to mid-grey tone and an increase in all particle sizes except for sand, medium silt, and fine silt (Fig. 5.10). All geochemical elements except for sodium and potassium show a maximum in concentration (Fig. 5.11). Exceptions to 124 Concentration (mg/kg) Figure 5.11: Geochemical stratigraphy of core T9. Note: precision is within 5% for all elements except calcium which has a precision values of 5.1 and 5.4%. Cadmium and lead concentrations fell below detection levels. 126 CN CN \ CN \ I " CN \ / \ r O V i \ / • CN I r 0 0 A 1 ' H , — J L j , ) 1 1 , co 1 -9 , 5 i i J i i , ' CN CO oo CM CM m o m (uio) indop o CM CO CM O CM CO 0) c 8 o 'c ra B O ' 9 1 : K L: i-CM CN CN O CN 0 0 o CM m CM (/> c CD to 0 CD CD ra C L — 1 D co x: D * -H CD C CO * i to C 0 1 o o $ o J,m O TO NT : ~ CD .9? 3 S i b .ra c g co c 'co > .2 .2 .3 ra j-= o o ra o £ C L o w TJ -T3 CD CD CO CD CD Q •— o ° o> O T J m c <D 5 C CD ro o _ o co 6 Q c\i •. S> o LO co CD to E T CD O .2> o TJ L L O X ) (LUO) indap 127 r-it" 1- \ • 1 H • i in o in CM CM (wo) ujdap 1 -CN 0 0 h-CM ^ — 00 o CM h-cq o o \— CM oq o T — CD H d o CM CM 00 O CM 00 O o CN 00 O CD O CN 2 "E i o 3 •s. CD U CO 3 ( 0 u Q) C U) co oo d T— T— CM CM (wo) indap co o co o <D o i _ o c O co ( 0 co-p 2 0 8 1 ^ CO >* -.t=: co = CD -Q u. o CL O CD r -O •-CO CO =3 5 CO -O O) "3 CO CD 0 * ^ 2 1 8-CO ->-J co i — J5 £ CD CO sz CO c S 8 P o o c o — CO C ti CD > ( ] ) * = Q 0 ) Q-0 0 O CO 1 0 CD "D CD O)co LL CO C 128 the pattern in Zone M-D are discrete layers visible in cores T8 and T10 and stable magnetic susceptibility in core T2 (Appendix B and Fig. 5.13). Comparison of organic content profiles of all cores (Fig. 5.12) shows good correlation across the lake. While lake-wide correlation of magnetic susceptibility profiles is more difficult (Fig. 5.13), the persistence of the trends identified above justifies the definition of the four sedimentary zones. 5 . 3 . 3 . Sediment Chronology In addition to the discrepancy between the two isotope records discussed in section 5.1.2, the correlated sedimentary zones identified in cores T2 and T10 have very different 2I0Pb ages (Fig. 5.1b). Considering the uncertainties and discrepancies in the 210Pb derived ages, and the relatively poor correspondence with the I37Cs markers, any calculation of sedimentation rate and sediment yield would yield tenuous data without the use of another chronological control. In addition, even if the 137Cs markers are deemed more reliable, they are relatively meaningless. Both occur in Zone T-D, thereby making any cross-zone analysis impossible. Moreover, forestry-related activity began well after 1963, making any assessment of the effects of disturbance also impossible. 5 . 4 . K I T E L A K E Three cores were collected in Kite Lake. Cores KI and K4 are half the length of K2 (Appendix B). Core K4 experienced some disturbance during the coring process. 129 5.4.1. General Stratigraphy Stratigraphic markers are very limited in x-ray images of Kite Lake cores. Cores Kl and K2 are light grey with specks of white to light grey throughout, while the x-ray image of K4 exhibits more variability in grey tone with contrasted and crude layering. All three cores are noticeably sandy and rich in macro-organics. A barely visible layer of sand divides the downcore profile of K2 approximately 14 cm from the top of the core (Fig 5.14). 5.4.2. Sediment Properties Kite lake sediments have high concentrations of macro-organic particles and a relatively coarse minerogenic component. Bulk density averages 0.29 g cm"3, while total residual moisture averages 80% (Table 5.5). Magnetic susceptibility is remarkably non-varying between 0.1 and 0.2 xlO"6 m3 kg"1 with an increase in the most recent sediments causing a slightly higher average value (Table 5.5). K2 was chosen as the representative core of Kite Lake due to its length compared to the other two much shorter cores and due to its central location. Core K4 is located immediately west of the Lucky creek delta and it is thus unlikely to be characteristic of the conditions in the remainder of the lake. Three sedimentary zones are defined on the basis of organic content and magnetic susceptibility in core K2. The definition of lake-wide stratigraphic zones is limited as cores Kl and K4 are much shorter than core K2 (Fig. 5.15). The following discussion on the sediment properties of Kite Lake sediments is thus based almost entirely on the sediment record of core K2. 130 Figure 5.14: X - ray image of core K 2 . Note the sandy layer and the graded nature of the zone boundar ies. 131 K 1 K 2 K 4 0 25 H — i — i — i — i — i — I - I — i — i — i — i — i— • — I -J—i—i—i—i—t—i—i—I 34 36 38 40 33 35 37 39 14 18 22 26 28 Organic content (%LOI) K 2 K 4 9 J K-B — i — i — i — i — i — I K -A 1 — i — 1 — i — i — i — 4 0 0.2 0.4 0.6 0.2 0.4 0.6 0.8 Magnetic susceptibility (x 10 m kg") Figure 5.15: Downcore and spatial variability of organic content and magnet ic susceptibi l i ty in Kite Lake cores, showing lack of c ross-core correlat ion. C o r e s are ar ranged to reflect location in the lake (Fig. 4.20). 132 Table 5.5: Average values (± standard deviation) of core K2's sediment properties Sediment property K2 Organic content (%LOI) 37± 1.8 Bulk density (g cm'3) 0.29 ± 0.02 Total residual moisture (%) 80 ± 1.3 Hygroscopic moisture (%) 5.6 ±0.40 Magnetic susceptibility (xlO"6 m3 kg"1) 0.23 ±0.10 SIRM/Xo ratio (k Am"1) 18 ±2.6 content, and moisture (Fig. 5.16). Bulk density slightly decreases in this zone, with values ranging between 0.30 and 0.25 g cm"3, while magnetic susceptibility displays a slight increase. The sandy lamina in its upper section, barely visible on the x-ray image, corresponds to a low in organic content (Fig 5.14, 5.16). The thinner Zone K-B (5 5-9.9 cm depth) is characterized by relatively non-varying trends in almost all sediment properties, with exception of bulk density and SIRM/Xo which both increase. While magnetic susceptibility remains stable, the values obtained in this zone are slightly higher than those found in Zone K-A. The mid to dark grey tone of the zone below grades into a mid to light grey tone for Zone K-B (Fig. 5.16). The uppermost sedimentary Zone K-C which extends from the surface down to 5.5 cm depth is characterized by an increase in magnetic susceptibility. The zone has a mid to dark grey tone, and exhibits a peak in organic content and hygroscopic moisture, decreasing total residual moisture and increasing bulk density (Fig. 5.16). 5 . 4 . 3 . Sediment Chronology The 210Pb chronology is adopted as the 137Cs profile appears seems to have been affected 134 by both downward mobility and upward tailing of the 1963 peak from catchment derived 137Cs (see section 5.1.2., Fig. 5. lc). Based on these data, the following dates are assigned to the sedimentary zones of core K2. Table 5.6: Ages of the sedimentary zones identified in core K2. Zone Age K-C 1997-1978 K-B 1978-1955 K-A 1955-1830 Note: the ages of K - C and K - B boundaries are very similar to the ages of boundaries in Maggie Lake. 5.4.4. Sediment Accumulation Rates and Sediment Yield Accumulation rates calculated for the dated master core K2 show a general increase upcore from 0.01 g/m2/yr at the base of the core to 0.05 g/m2/yr at the top of the core (Fig. 5.17). A maximum accumulation rate between 1917-1921 is found in Zone K-A stratigraphically below the marker horizon described in the previous section. Accumulation rates in K2 slowly increased between 1921 and 1978. A sharper increase is noted in the uppermost layer of the core. Trap efficiency estimates are 56 to 84 % based on a range in discharge of 0.8-4.0 m3/s (Appendix F). Over the period of deposition of the three zones, catchment sediment yields range between 90 and 580 g/yr/km2 (Table 5.7). The wide range in the trap efficiency estimates leads to a difference of 50% between the maximum and minimum values of sediment yield. The adoption of a more constrained lake sediment depositional area leads to a 44% decrease in the sediment yield estimates. Zone K-A exhibits the lowest sediment yield. Zones K-B, K-C (b) and K-C (a), K2 o E o Q. CD Q 15 20 10 1983-88 i 1949-55 1917-21 1855-73 25 K-C K-B 1978 1955 K-A 1830 0 0.02 0.04 0.06 Accumulation rate (g m"2 yr"1) Figure 5.17: Temporal variability in sediment accumulat ion rate in core K2 based on Lead-210 dates. Shad ing highlights peaks in accumulat ion rates. 136 Table 5.7: Sediment yield for Kite Lake catchment. Minimum and maximum values are based on Zone Date Min. Yield-10 Max. Yield-10 Change from change (Wvr/km*> fo/yr/km2) zone below* from K-A* K-C(a) 1997-1988 387 580 1.73 4.3 K-C(b) 1988-1978 224 335 1.41 2.49 K-B 1978-1955 158 237 1.76 1.76 K-A 1955-1830 90 135 Zone Date Min. Yield-20 Max. Yield-20 Change from change <Vvr/km2>> [V/vr/km*> zone below* from K-A* K-C(a) 1997-1988 215 322 1.73 4.3 K-C(b) 1988-1978 124 186 1.41 2.49 K-B 1978-1955 88 132 1.76 1.76 K-A 1955-1830 50 75 *Factor by which yield changes from previous zone or compared to Zone K-A. -Estimates of sediment yield were calculated assuming deposition over an area delimited by the 10 m contour and over an area delimited by the 20 m depth contour. -Units differ from those used in the other two lakes due to the much lower magnitude of sediment yield in this basin. -Sediment yield calculation data is in Appendix G. show greater sediment yields with the highest increase from levels in Zone K-A observed in the last nine years of deposition (Table 5.7). Zone K-C was divided into two sub-zones to resolve the change in sediment yield since logging began in the early 1990s. This calculation was possible as there is only one core from which to extrapolate accumulation rates to the whole lake. This subdivision reveals that the increase in catchment sediment yield from Zone K-A to Zone K-B is not sustained to the same degree in Zone K-C(b) (Table 5.7). 5.5. C L A Y O Q U O T L A K E Three cores of comparable length (avg. 24 cm) were collected in the lower basin of Clayoquot Lake. Minimal disturbance was caused by coring as evident from the downcore drag of the layer visible at the base of core C3 (Fig 5.18). 137 C 3 Zone C - C Zone C - B Zone C - A Figure 5.18: X- ray image of core C 3 . Note the sandy-organic rich marker at base of Zone C - A . 138 5.5.1. General Stratigraphy X-ray images reveal a relatively uniform grey tone downcore with the exception of one discrete darker grey layer, 1-1.5 cm in thickness, which occurs at the base of cores CI and C3 (Fig. 5.18). This discrete layer is characterized by sand and macro-organic fragments and is underlain by a thick layer of sand in core CI (Appendix B). Crude layering with varying grey tones is evident in the upper section of cores CI and C2 (see Appendix B). 5.5.2. Sediment Properties Sediments are typically composed of fine silt and gyttja. Average values of sediment properties are summarized in Table 5.8. Bulk density is remarkably non-varying throughout all cores with an average value of 0.43 g cm"3. While some of the elements exhibit similar profiles, trends of the other major elements are quite variable. SIRM/Xo is mostly variable across cores, although spikes in this parameter are inversely related to spikes in magnetic susceptibility and correspond to some spikes in organic content. For the purpose of the more detailed discussion of sediment properties, core C3 was selected as a representative core as it is well correlated to the dated master core CI. Table 5.8: Average values (± standard deviation) of sediment properties of all Clayoquot cores and core C3. Sediment Property ALL CLAYOQUOT CORES C3 Organic content (%LOI) 25 ±2.0 25 ± 0.97 Bulk density (g cm"3) 0.42 ± 0.05 0.43 ± 0.03 Total residual moisture (%) 71 ±2.8 71 ± 1.8 Hygroscopic moisture (%) 3.7 ±0.42 3.8 ±0.20 Magnetic susceptibility (xlO"6 m3 kg"1 ) 0.86 ±0.13 0.82 ±0.06 SIRM/Xo ratio (k Am"1) 20 ± 2.7 21 ± 1.5 139 Four sedimentary zones based on organic content trends are used to describe the sediment properties of Clayoquot Lake sediments. In core C3, the mid-to light grey Zone C-A (10.5- 18.7 cm depth) is characterized by a low in organic content and moisture, a relatively non-varying bulk density and increasing magnetic susceptibility (Fig. 5.19). All particle sizes are relatively constant in this zone except for slight increases in sand and medium silt in the top portion of the unit. Geochemical element concentrations reach a high in this zone, although cadmium, silica and potassium do not follow this pattern (Fig. 5.20). The peak in concentration of most elements which occurs just above 15 cm depth coincides with a peak in organic content. The base of Zone C-A is dominated by a sand marker at 19 cm depth which exhibits low organic content, high density, increasing to high magnetic susceptibility and a low in SIRM/Xo (Fig 5.19). Sand and coarse silt are relatively higher in concentration at this depth (Fig. 5.19). The low concentrations of most geochemical elements found at the base of Zone C-A coincide with the high sand content associated with the stratigraphic marker. This discrete layer is not visible on the x-ray image of core C2 but the trends in the other sediment properties of core C2 conform nonetheless with the above pattern (Appendix C, Fig. 5.21). The light grey Zone C-B (6.6-10.5 cm depth) is characterized by a maximum in organic content, increasing magnetic susceptibility and low to non-varying bulk density (Fig. 5.19). Changes in grey tone between this zone and the ones above and below are graded. Most particle size fractions remain the same except for an increase in very fine silt in the middle of the zone. Most major chemical elements decrease in concentration, while trends in heavy metals are highly variable (Fig. 5.20). In terms of cross-core variability, this zone is slightly darker in grey tone in core C2 and is better defined in terms of grey tone changes in core CI (Appendix B). In addition, 140 Figure 5.20: Geochem ica l stratigraphy of core C 3 . Prec is ion is within 5%, except for sod ium and potassium which have 5-6% precis ion levels. The poor precis ion level in the measurement of C d is offset by its c lose correlation with other e lements. 1 Magnetic Susceptibility (x 10"* m'kg"1) Figure 5.21: Downcore and spatial variability in organic content and magnet ic susceptibi l i ty of Clayoquot Lake cores. C o r e s are arranged to reflect location in the lake (Fig. 4.22). 143 this zone is much thinner in core CI and relatively thicker in core C2 (Fig. 5.21). Zone C-C which extends from the surface down to 6.6 cm depth is characterized by a minimum in organic content and moisture and a maximum in magnetic susceptibility (Fig. 5.19). Bulk density remains the same compared to the two other zones below, except for a decrease in the uppermost data point. X-ray images show this sedimentary zone to be visibly darker than the ones below. The three coarsest particle sizes as well as very fine silt increase in Zone C-C. Major chemical element and heavy metal concentrations decrease except for iron, manganese and potassium (Fig. 5. 20). Based on organic content and magnetic susceptibility, cross-core variability is limited in Clayoquot Lake (Fig. 5.21). Cross-core correlation of magnetic susceptibility in the uppermost zone is less well defined than in other zones. The relatively few cross-core inconsistencies in the stratigraphic patterns outlined above justify the definition of the three sedimentary zones. 5 . 5 . 3 . Sediment Chronology The lead-210 chronology was adopted as downward mobility of Cs-137 most likely accounts for the discrepancy between the two chronologies (Fig. 5. Ic; Table 5.9). Table 5.9: Ages of sedimentary zones in Clayoquot cores. Zone Age C-C 1997-1963 C-B 1963-1942 C-A 1942-1878 Note: the ages of C-C and C-B boundaries are very similar to the ages of boundaries in Maggie Lake. 144 5.5.4. Sediment Accumulation Rates and Sediment Yield Accumulation rates in the dated master core CI are relatively non-varying throughout the last 120 years, with a slight increase since 1974 (Figure 5.22). A period of higher accumulation rates occurs in zone C-A between 1929 andl935. Sediment yield estimates range between 1.7 and 3.7 t/yr/km2 over the period of deposition of the three zones (Table 5.10). The trap efficiency of Clayoquot Lake is the same as that of Kite Lake with estimates ranging between 56 and 84% based on estimated discharges of 1.9 to 9.3 m3/s (see Appendix F). This wide range in trap efficiency leads to a 55% difference between the maximum and minimum sediment yield estimates (Table 5.10). An area of no sediment accumulation down to depths of 20 m instead of 10 m leads to a 21 to 22% decrease in yield estimates . Zone C-B shows a sediment yield 1.4 times that observed in Zone C-A. Catchment sediment yields remain high but show a slight decrease between Zone C-B and Zone C-C. Table 5.10: Sediment yield for Clayoquot Lake catchment. Minimum and maximum values are Zone Date Min. Yield-10 Max. Yield-10 change from change rt/vr/km2) ft/vr/km2) zone below* from C-A* C-C 1997-1963 2.2 3.4 0.9 1.28 C-B 1963-1942 2.4 3.7 1.4 1.4 C-A 1942-1878 1.7 2.6 Zone Date Min. Yield-20 Max. Yield-20 change from change rt/vr/km2) (r/vr/km2>l ••one below* from C-A* C-C 1997-1963 1.7 2.6 0.9 1.24 C-B 1963-1942 1.9 2.8 1.4 1.4 C-A 1942-1878 1.4 2.1 •Factor by which yield changes from previous zone or compared to Zone C-A. -Estimates of sediment yield were calculated assuming deposition over an area delimited by the 10 m contour and over an area delimited by the 20 m depth contour. -Sediment yield calculation data is in Appendix G. 145 C1 o E o Q_ O Q 10 15 20 25 • • 1981-1996 C-C 1 v i I C-B 1 1929-1935 • i C-A I H - * 1878-1911 • 1 1 1 l 1963 1942 1878 0 0.1 0.2 Accumulation rate (g m"2 yr'1) Figure 5.22: Temporal variability in sediment accumulat ion rate in core C1 based on lead-210 dates. Shad ing highlights changes in rates. 146 5.6. CROSS LAKE COMPARISON Thirty five cores were collected in the four lakes at average depths ranging between 13 and 39 m (Table 5.11). Most cores were approximately 20 cm long except for those collected in Maggie Lake which were generally longer. Coring density is comparable between the four basins. While there are some similarities, most sediment properties display unique trends in each lake. Magnitude of organic content is low in Maggie Lake sediments and relatively high in Kite Lake sediments (Table 5.12). This cross-lake pattern is also evident for hygroscopic moisture and total residual moisture. Average values of bulk density and magnetic susceptibility are highest in Maggie Lake and lowest in Kite Lake. Average values of all sediment properties of Toquart Lake are within the same range as those found in Maggie Lake, while those of Clayoquot Lake are comparable in magnitude to those found in Kite Lake. The average susceptibility of Kite Lake sediments is much lower than in all three other lakes (Table 5.12). Particle size distribution is Table 5.11: Summary of coring data. Data type Maggie L. Toquart L. Kite L. Clayoquot L. Number of cores 17 11 3 3 Average length 31 23 20 24 of cores (cm) Average depth (m) 39 30 13 37 Lake area / core 12.9 9.1 6.7 9.0* (ha) *Value is based on the area of the lower basin rather than the total lake area since upper basin was not cored. -Note that average length refers to length prior to freezing. relatively well distributed over all size fractions in Maggie Lake, whereas it is dominated by fine silt in both Toquart and Clayoquot. 147 Table 5.12: Average values (± standard deviation) of sediment properties of all cores in each lake Sediment Property MAGGIE TOQUART KITE CLAYOQUOT Organic content (%LOI) 15 ±5.7 20 ±3.0 37 ± 1.8 25 ± 2.0 Bulk density (g cm"3) 0.65 ±0.17 0.52 ±0.09 0.29 ± 0.02 0.42 ± 0.05 Total residual moisture (%) 58 ±8.6 65 ±3.1 80 ± 1.3 71 ±2.8 Hygroscopic moisture (%) 2.5 ±0.93 3.1 ± .55 6.0 ±0.4 3.7 ±0.42 Magnetic susceptibility 1.75 ±0.71 1.3 ±0.14 0.23 ±0.10 0.86 ±0.13 (xlO"6 m3 kg1) SIRM/Xo ratio (k Am"1) 13 ±3.1 23 ±3.5 18 ±2.6 20 ±2.7 The most significant similarity is that displayed by the sedimentary zones of Clayoquot Lake and Toquart Lake. Organic content trends in these two lakes are particularly similar with a peak within the sedimentary zone C-B and T-C (Fig 5.12 and 5.21). In contrast, the downcore profiles of organic content found in Maggie Lake are more complex, while that of core K2 is somewhat cyclical (Fig. 5.5 and 5.15). While both Maggie Lake cores and Clayoquot Lake cores have a minerogenic stratigraphic marker at the base of their sediment record, the one in Clayoquot Lake is older (1878). The period of high accumulation rate in Clayoquot Lake's Zone C-A corresponds to the dated marker horizon in Kite Lake's core K2 (1929-1935 and 1927-1935 respectively). Almost all upper sections of cores in Clayoquot, Kite and Toquart lake exhibit a darker x-ray grey tone. In contrast, the change to darker tones occurs much earlier in the sediment record of Maggie Lake (1944-1951 in core M5 and 1962 in core M16). All four lakes exhibit unique downcore trends in magnetic susceptibility. The maximum magnetic susceptibility encountered in Maggie Lake differs markedly from maximum values obtained in the other three lakes. 148 Lastly, in terms of chemical stratigraphy, there are essentially no similarities between the downcore trends of major elements and heavy metals between the four lake sediment records. Highest concentrations of major elements and heavy metals are found in Clayoquot Lake, except for potassium and cadmium which are highest in Maggie Lake, and manganese, which is highest in Toquart Lake. The next highest concentrations are usually found in core T9 while core Ml2 concentrations are usually higher than those of core Ml 8. Magnesium and silica concentrations are substantially lower in Ml 8, while iron concentrations are substantially lower in T9. Sediment yields from the catchment of Maggie Lake are an order of magnitude higher than those observed in Clayoquot Lake. Sediment yields from the Kite Lake catchment are 104-10s lower in magnitude than in the other two lake basins. Cross-lake comparisons can only be made for zones which are synchronous across lakes. Sediment yield in Kite Lake was therefore recalculated to match the chronological boundaries in the other two lakes, thereby allowing cross-lake comparisons. Sediment yield estimates in Maggie and Clayoquot lake basins are based on multiple cores for zones which are correlated by sedimentary characteristics. Comparisons are therefore limited to zones which are fortuitously synchronous in the two lakes. The period of 1953-1961 in the Maggie watershed records a greater increase in sediment yield from the previous period (1943-1953) than it does in the Kite Lake watershed (Table 5.13). Sediment yield continues to increase from 1961 to 1997 in Kite Lake, compared to decreases in sediment yield in the watershed of Maggie Lake for the same period. Increases in sediment yield in Kite and Clayoquot basins are comparable during the period of 1942-1963 (Table 5.13). The period from 1963 to the present shows an increase in sediment yield from the previous period by a factor of 1.6 in Kite Lake and a decrease by a factor of 0.9 in Clayoquot Lake. Lastly, the post 1963 decrease in sediment yield observed in the Maggie Lake basin is relatively similar to the one 149 Table 5.13: Comparison of sediment yield changes over time in the three watersheds. Time Period Change* from previous period Change* from oldest period 1997-1979 (Maggie) 0.7 0.6t 1997-1978(Kite) 1.77 2.16t 1979-1961 (Maggie) 0.7 0.9t 1978-1961 (Kite) 1.15 1.2t 1961-1953 (Maggie) 1.4 1.4t 1961-1952 (Kite) 1.1 l i t 1997-1963 (Kite) 1.6 2.4t 1997-1963 (Clayoquot) 0.9 1.2* 1963-1942 (Kite) 1.5 i n 1963-1942 (Clayoquot) 1.4 1.4J 1997-1961 (Maggie) 0.7 (M-D), 0.7 (M-C) (not comparable) 1997-1963 (Clayoquot) 0.9 (C-C) •factor by which sediment yield changes from previous period or from oldest period, f change from the oldest period 1943-1953. j change from the oldest period 1942-1873 (Kite)/ 1942-1878 (Clayoquot). -See Appendix G for adjusted Kite Lake sediment yield values.observed in the Clayoquot Lake basin. 5.7. MAGNETIC PROPERTIES OF TERRESTRIAL MATERIALS Three different types of terrestrial materials were collected in each basin (Table 5.14). Most of these were obtained from exposures along roads of the three logged basins and along the creeks and lake shoreline of Clayoquot Lake's watershed (Fig. 5.23). It should be noted that multiple soil samples were collected at one site so that the number of sites where soil was collected is lower than the value reported in Table 5.14. Kite Lake watershed ) / "III, /Handsome ( [ Mountain Lucky .3 Mountain! ^ ^ ^ ^ Lake / \ J Black Peak 0 1 2 3 km . sample site location 150 Toquart Lake Clayoquot Lake watershed i Norgar T \ I \Lake ( 45-18T w ^ ^ V v / p ^ H - 9 - 1 3 O / Clayoquot Lake^ Hidden Peak Figure 5.23: Locat ion of the terrestrial surface material samp les from the four study watersheds. 151 Table 5.14: Types and numbers of terrestrial material samples collected in each lake basin. LAKE BASIN DATA Maggie L. Toquart L. Kite L. Clayoquot L. Soil samples 13 9 10 2 Bedrock 7 4 5 6 Unconsolidated sediments 5 9 2 9 Total surface material samples 25 22 17 17 Terrestrial area / sample (ha) 228 309 147 394 Bedrock specimens have mostly low values of magnetic susceptibility (1 x 10"6 - 1 x 10"7 m3kg"1) with some exceptions (on the order of 1 x 10 "'nr'kg'1) (Appendix H). This is prevalent for bedrock from all watersheds except Toquart which only has low values. SIRM/ Xo ratio for bedrock specimens exhibit low values ranging from 1-5 kAm"1, with some exceptions ranging from 10-50 kAm"1. The magnetic susceptibility of soils is relatively similar across the four watersheds with average values of 1 x lO t^o 1 x 10'7 m3kg'1. The SIRM/Xo ratios of soils are variable across the four lakes: high in the watersheds of Clayoquot and Kite lakes, low in Maggie and mixed in Toquart (Appendix H). There seems to be no significant relation between magnetic properties and the parent material of the soil (e.g. soil on rock versus soil on till). The standard enhancement of magnetic susceptibility in topsoil due to the formation of magnetite and maghemite is observed only in some of the surveyed soil profiles. This may be explained by the fact that Ferro-Humic Podzols dominate the study region. Most of the iron oxides in these soils are leached out of the uppermost layer and accumulate lower down in the soil 152 profile, leading to higher magnetic susceptibility values lower down in podzolic profiles. The sample results which do not conform to this pattern may be due to local differences in degrees of leaching. Clays, gravels and gully bank materials tend to have high SIRM/Xo ratios, tills and sand have intermediate SIRM/Xo ratios, and colluvium has lower SIRM/Xo ratios (Appendix H). These materials all have relatively similar values of magnetic susceptibility. SIRM/Xo ratios of terrestrial materials reveal significant differences in each basin (Table 5.15). Low SIRM/Xo are associated with colluvium in Clayoquot valley and stand in contrast to soils and fluvial sediment values (Table 5.15). The watershed of Kite Lake is characterized by generally higher SIRM/Xo ratios for soils. Soils on clays also have higher SIRM/Xo ratios than soil on bedrock or on other materials (Appendix H). The SIRM/Xo ratio of laminated clays collected along Paradise Creek Road in the watershed of Maggie Lake are high in comparison to all other materials with a value of 45 kAm"1 (Appendix H). Magnetic properties of soils on bedrock in the catchment of Maggie Lake are not substantially different from those on till or granules (Table 5.15). SIRM/Xo ratios in Toquart are well differentiated across the different types of materials. Unconsolidated sediments have higher ratios than soils with the lowest values found in bedrock and glaciofluvial sand. 153 Table 5.15: Average SIRM/Xo ratio of terrestrial materials from each watershed. Watershed Material Type (# of samples) Average SIRM/Xo ± std Maggie bedrock* (2) 2± 1 soil on bedrock (5) 14 ± 2 soil on till (8) 14 ±5 other unconsolidated sediment (7) 13 ±3 Toquart bedrock (4) 4 ± 3 other unconsolidated sediment (5) 34 ± 11 soil (10) 20 ±5 sand (3) 12 ± 1 Kite bedrock* (4) 3 ± 4 soil (10) 43 ± 12 clay(l) 19 sand (1) 29 Clayoquot bedrock* (5) 3 ± 1 soil (2) 29 ±3 fluvial sediments (3) 24 ±8 colluvium (6) 6 ± 2 *One sample with an extreme value was not used in the calculation of average. - See Appendix H for complete data set. Chapter 6 The sedimentary signature of catchment disturbance 154 6.1 INTRODUCTION This chapter presents a final discussion of chronological control based on the identification of event markers, as well as the interpretation of the sediment record, thereby documenting the correspondence between changes in the lake sediments and the historical records of disturbance. Trends in sediment yield that depart from the regional trend, the occurrence of marker layers and the general trend in sediment properties are interpreted in the light of the catchment disturbance history. The last part of the chapter addresses the methodological issues identified in chapter 1, including the appropriateness of this approach in monitoring the effects of forestry activity. 6.1.1. The Potential Bias of the Sediment Chronology Several marker layers were identified in the sediment records of the four study lakes. These provide an opportunity to assess the potential bias of the 210Pb chronology. An event in the period 1927/9-1935 is recorded as a discrete clastic layer in Kite Lake and an increase in sediment accumulation rate in Clayoquot Lake. While the exercise remains purely speculative for the lack of historical records over this period, it is useful to consider the origin of this event in an attempt to check the accuracy of the 210Pb chronology. A particularly severe rainstorm or an earthquake, could have generated landslides events throughout the region, which in turn may have been recorded in the lake sediments. In January 1935, the storm of the century occurred on the inner coast of British Columbia (pers.comm. M. Church, 1997). Moreover, Mathews (1979) documented the widespread occurrence of landslides following the 1946 earthquake on the 155 eastern coast of Vancouver Island. Both of these natural disturbances may account for the event layer. If the event corresponds to the 1946 earthquake, the inaccuracy of the 210Pb chronology yields underestimates of sediment accumulation. If on the other hand, the 1935 storm of the century is responsible for the sedimentary marker, the 210Pb chronology is relatively accurate. Another regional event which may be responsible for changes observed in the sediment record is Hurricane Freda, which occurred in 1962. In the Maggie Lake cores, this event coincides with other disturbances associated with logging and mining in the catchment, so that its influence on the record is difficult to assess. However, high influxes of organic matter are recorded in the period 1942-1963 in Clayoquot Lake and 1955-1961 in Kite Lake. It is plausible that Hurricane Freda caused greater mobilization, transfer and delivery of organic matter to the lakes. In either lake, the 210Pb chronology returns older ages showing a possible underestimate of sediment accumulation. A final example illustrates the potential bias of the adopted 210Pb chronologies. The pronounced nature of the magnetic susceptibility peak in Zone M-B can be explained in several ways. Increases in magnetic susceptibility have been interpreted as resulting from periods of accelerated erosion associated with human disturbance (Thompson et al, 1975; Dearing et al., 1981; and O'Hara etal, 1993). In addition, however, iron ore was mined just north of Maggie Lake. Draw Creek was previously known as Magnetic Creek in the early part of this century when a strong magnetic anomaly was reported by prospectors (Mines and Petroleum Resources Report, 1961). Over 5 million tons of iron ore were then exported during the operation of the mine from 1962-1969 (Ministry of Forests, 1993). Thus, the increase in the magnetic susceptibility of Maggie Lake's sediments may have been related to both mining and accelerated erosion associated with forestry activity. 156 It is reasonable to assume that sediments mobilized as a result of Hurricane Freda influenced the nature of the magnetic signature found in this period, but that the most likely factor remains the upstream mining of magnetite-rich bedrock. The shear magnitude of the peak compared to the much lower susceptibilities found in other lakes supports this assertion. Consequently, the peak in magnetic susceptibility can be used as a check on the 210Pb chronology. The mine was in operation between 1962 and 1969. The onset of the rise in magnetic susceptibility can therefore be assigned a tentative date of 1962. The possibility of continued erosion of magnetite-rich bedrock following closure of the mine makes the dating of the upper tail of the peak more difficult. This process may account for the higher level of magnetic susceptibility in Zones M-C and M-D compared to that found in M-A. However, the relatively sharp decrease following the peak suggests that the process was limited. As a result, it is plausible to assume that the upper tail of the peak corresponds to the early seventies. The 210Pb age of the peak is 1940 to 1969, and 1953 to 1977 in cores M5 and Ml 6 respectively. This provides further evidence for the potential bias of 210Pb in underestimating sediment accumulation. The sensitivity analysis of core T10 to the doubling of the 210Pb activity in the top layer of the core yielded overestimates of sediment accumulation. As the analyses of event markers indicate consistent underestimates of sediment accumulation, it is suggested that the second assumption, which concerns the estimate of the bottom of the isotopic profile, is the more likely source of the 210Pb bias in the cores of Maggie Lake, Kite Lake and Clayoquot Lake. The inconsistent magnitude of the offset points to the possible interplay of uncertainties associated with both assumptions. The discussion of some of the problems and inherent uncertainties in the dating techniques identifies some of the limits and constraints on the chronological control of the sediment record. 157 The analysis of event markers suggests that layers or zonal boundaries may be more recent than the 210Pb data suggests. As a result, connection between changes in the sediment record and changes in land-use history may be made erroneously. In particular, a change may appear to have occurred earlier than it really did. In addition, sediment yield estimates in Maggie Lake, Kite Lake and Clayoquot Lake may be underestimated. The interpretation of the sediment record which follows is constrained by these qualifications. 6.1.2. The Interpretation of the Sediment Record The interpretation of the sediment record is based on the following general principles. Relative importance of the clastic and organic component of the sediment is derived from trends in clastic sediment yield, magnetic susceptibility and loss on ignition data. Increases in magnetic susceptibility are interpreted as increases in magnetite-rich clastic sediments (Thompson etal., 1975; Dearing etal, 1981; Oldfield etal, 1983). Changes in organic content are also relevant in this study where abundance of organic debris following timber harvesting may have an effect on organic influx to the lake. Increases in particle size represent changes from relatively quiet depositional conditions to ones of higher energy. The relation between sediment geochemistry and depositional conditions is complex. However, similarity between elements suggests their association with a particular sediment source which is characterized by a certain assemblage of elements. In this study, elemental concentrations are often related to organic content. Deviations from this trend are interpreted as a change in sediment source where some of the elements may be associated with a particular minerogenic source. Due to the interdependence of chemical constituents of sediments (Jacquet et al, 1982), an increase in several elements may be explained in two different ways: an actual 158 increase in the influx of these elements or a relative increase as a result of an actual decrease of other elements. Either explanation is the result of a change in sediment source; the difficulty lies in distinguishing which elements have actually changed. Comparison of the variability in all sediment properties can help identify the source of change. The comparison of the SIRM/Xo ratio of lake sediments and terrestrial materials is more useful to assess the relative importance of the various terrestrial clastic sediment sources. Secondary magnetic oxides which form in soils differ in crystal form and size from those in primary magnetic minerals found in parent materials (Oldfield, et al, 1983). Thus shifts in SIRM/Xo ratio of the lake sediments are interpreted as changes in sediment sources. 6.2. T H E REGIONAL TREND IN SEDIMENTATION The connection between changes in the sediment record and catchment disturbance can be made only in the context of regional trends. Thus the interpretation of the sediment record begins with the establishment of the regional trend in sedimentation. This is achieved through the interpretation of the sediment record of Clayoquot Lake and the interpretation of the trends observed in Kite Lake over the period preceding the onset of forestry activity. 6.2.1. The Sediment Record of Clayoquot Lake The Period 1878-1942: Zone C-A, which documents sediment deposition between 1878 and 1942, shows an increasing trend in magnetite-rich sediment influx and a relatively constant or increasing trend in organic content. High accumulation rates between 1929 and 1935 point to a period of higher minerogenic influx. Increases in sand and medium silt fractions near the top of the zone coincide with the occurrence of landslides reported between 1939 and 1957. 159 Interpretation of the sediment geochemistry is limited since element concentrations are strongly associated with organic content. The marker layer which occurred between 1878 and 1896 represents a depositional event of both organic debris and minerogenic particles. The additional layer made up almost entirely of sand in core CI points to a source in the lower part of the lower basin. Records of natural disturbance in the watershed show that eight landslides occurred prior to 1939 at the head of the creek which flows into the lower part of the lower basin. While core CI is not located in line with the inflowing creek, it is the most likely to be affected by sediment influx related to landslides and debris flows moving down the creek and into the lake. The thickness of the sand layer and the relative lack of smaller particles in core CI, and the thickness of the marker layer in the other two cores suggests that this was a high energy and large sediment-producing event. The absence of a similar layer in the record of core K2 suggests that the event was localized rather than regional in its extent. The Period 1942-1963: Zone C-B (1942-1963) is characterized by an increase in sediment yield and the intensification of the rising trend of magnetite-rich clastic sediment influx as well as a high in organic content. This is consistent with the natural disturbance history which reports a large number of landslides in the period 1939-1957. Of particular significance are the four landslides which occurred above the lake and along the creek which flows into the lake at the narrows. These landslides may be responsible for the observed 40% increase in sediment yield. Decreases in element concentrations suggest a change in sediment source. The Period 1963-1997: Zone C-C (1963-1997) is characterized by a slight decrease in catchment sediment yield. It also exhibits a magnetite-rich sediment fraction which is greater than the other two zones. This is supported by the darker grey tone, greater fractions of coarser 160 particles, high magnetic susceptibility and bulk density. This greater fraction of magnetite-rich sediments despite a decrease in sediment yield, can be explained by the continued (slower) delivery of these heavier minerals to the lake, which were probably first mobilized during the previous period of increased minerogenic influx. Organic matter concentration has decreased back to levels observed in Zone C-A. Iron, manganese and potassium all show a low and a subsequent increase in this zone. This may indicate an influx of sediment associated with surface erosion (Mackereth, 1966). It is interesting to note that the 1995 landslide which occurred above the lake did not result in an event layer at the top of the sediment record. Hydrological conditions at the time may have lead to rapid flushing of the expected sediment plume. Upstream storage does not seem like a valid explanation as the steep slopes are directly above the lake. While a change in sediment properties is not observed, a sharp rise in accumulation rate in the uppermost layer of core CI (Fig. 5.22) may be related to the 1995 landslide. Sediment Source: Distinction of sediment sources is most successful in this watershed where both colluvium and bedrock exhibit much lower values than soil or fluvial sediments. The average SIRM/Xo ratio of the lake sediments is lower than the average value for soil and fluvial sources, pointing to the influence of the parent material in determining the magnetic properties of the lake sediments. It is hard to distinguish between soil and fluvial sediment signals due to the limited number of terrestrial samples analysed and the wide range of values obtained for fluvial sediments (avg. 24 ± 8). The low SIRM/Xo value which coincides with the marker horizon at the base of Zone C-A points to colluvium and bedrock as significant sources of the minerogenic component of that layer. 161 6.2.2. The Sediment Record of Kite Lake Prior to 1978 The Period 1830-1955: Zone K-A which spans deposition from 1830 to 1955 records a period of increasing organic concentration and a much less marked increase in the inorganic component of the sediment. The amplitude of the fluctuations of organic content is within the range of the measurement error. However, the regularity of the fluctuation (19-22 years between maxima) suggests that these fluctuations are not an artifact of the measuring technique. The observed cyclicity may be related to precipitation patterns where recurring years of high precipitation mobilized and transferred more organic sediment to the lake. Conversely, lows in organic content may be a result of high precipitation which led to increased mobilization of minerogenic sediments and dilution of the organic component. The sediment marker in this bottom zone documents minerogenic influx between 1927 and 1935. The peak in accumulation rate just below this marker may be related to this event or may record an earlier event. As the other cores obtained from Kite Lake were much shorter, the lateral continuity of this discrete layer is uncertain. However, the central location of core K2, its relatively simple stratigraphy compared to core K4, which is near the inflow, and the simple bathymetry of this lake suggest that this event is probably not a localized feature. Its correlation with a period of high accumulation rate in Clayoquot lake suggests that it may be the result of a regional event. The Period 1955-1978: Zone K-B, which records deposition between 1955 and 1978, exhibits a higher overall clastic sediment yield, and a higher fraction of magnetite-rich sediment influx. While the x-ray image suggest that this zone is less dense than the one below, both magnetic susceptibility and bulk density supports the interpretation of higher minerogenic influx. Organic content stabilizes in this period. The lowermost maximum in organic content occurs only 162 10 years after the previous one of Zone K-A and therefore seems out of phase with the others. The date of this peak is 1955-1961 making Hurricane Freda a possible cause. The description of the most recent period of the Kite Lake record is deferred until after the regional trend has been established. Sediment Source: Upcore increases in the SIRM/Xo ratio point to an increase in the soil component. The average SIRM/Xo ratio (18 ± 3 kAm"1) is much lower than values observed in soil samples (43 ± 12 kAm"1). This is consistent with the trend identified in the control lake where weathering of the parent material (3± 4 kAm'1 in Kite Lake) and of other materials which have a lower SIRM/Xo ratio (e.g. clay) produces a significant amount of the sediment found in the lake. The contribution of unconsolidated glacial materials to lake sediments remains unknown. This is partly a function of the fact that none were collected for analysis. However, these materials are scarce in the Kite Lake watershed and their relative importance as a sediment source is most likely marginal. 6.2.3. The Inferred Regional Trend The earliest period recorded exhibits relatively constant to rising trends in magnetite-rich sediment and organic matter influx. A regional event is recorded over the period 1927/9-1935. The subsequent period of sediment deposition in Clayoquot Lake from 1942 to 1963 registered an increase in sediment yield and in the magnetite-rich fraction of sediments. The use of the 1953-1961 period in Kite Lake as a control for comparison with Maggie Lake is justified in two ways: increases in yield between the period 1942-1963 and thepre-\9A2 period are very similar in the sedimentary record of Clayoquot and Kite Lakes; the 1952-1961 period corresponds to one of the sedimentary zones in Maggie Lake, thus allowing a close comparison to be made. The 1952-1961 163 period records a slight increase in sediment yield, a high influx of organic matter and a rising trend in the magnetite-rich fraction of the minerogenic sediments. The regional event of Hurricane Freda in 1962 may partly explain this trend considering the potential bias of the 210Pb chronology. The regional trend for post 1961/1963 is more difficult to establish. Compared to the oldest period (1873/8-1942), both lakes experienced an increase in sediment yield over the period 1963 to the present. However, Kite Lake records an increase in sediment yield by a factor of 1.6, whereas Clayoquot Lake recorded a change in sediment yield by a factor of 0.9 from the previous period of 1942-1963. These values are not necessarily contradictory. The decrease in Clayoquot Lake only exists in proportion to the relatively high sediment yield of the previous period which was related to landslides in the watershed. Discrete local events may have partly contributed to the greater increase in sediment yield in the catchment of Kite Lake. 6.3. INTERPRETATION OF T H E POST 1978 RECORD OF KITE L A K E The increase in accumulation rate and sediment yield as well as changes in several sediment properties in Zone K-C reflect a marked increase in clastic sediments. The increase in susceptibility is most rapid in the uppermost two data points which record deposition since 1988. The increase in sediment yield, however from 1988 to 1997, is relatively similar in magnitude to increases observed during the period which precedes logging activity in the catchment. The sediment yield estimates of Kite Lake and Clayoquot Lake over the period 1963-1997 compared with those of 1873/8-1942 show that the increase recorded in Kite Lake is in fact significantly higher than that found in Clayoquot Lake. Considering the potential bias of the 210Pb chronology, the recorded increase over the period 1988-1997 may have occurred more recently. This increase in sediment yield would then coincide with the onset of logging activity in the Kite Lake 164 watershed. Upcore increase in the SIRM/Xo ratio points to an increasing influence of soil over parent materials. Based on these lines of evidence, it is plausible to assume that the changes recorded in the uppermost layers of the sediment record of Kite Lake are associated with forestry activity in that watershed. Organic content is relatively stable. The uppermost high in organic content, however, which corresponds to 1988-1993, is significantly larger in amplitude than those observed in zones K-A and K-B. Windthrow was particularly severe, destroying the buffer which had been left at the shore line and producing considerable amounts of woody debris following harvesting of the slopes adjacent to Kite Lake in 1992 (Fig. 4.13). Therefore, this high influx in organic matter is plausibly related to the effects of timber harvesting (Fig. 4.12). 6.4. INTERPRETATION OF THE SEDIMENT RECORD OF MAGGIE L A K E 6.4.1. The Period 1943-1953 Zone M-A, which represents deposition prior to 1953, is characterized by stable fractions of magnetite-rich sediments and decreasing to stable fractions of organic matter. The lake-wide discrete layer which occurs in this zone represents an influx of minerogenic sediment, which is followed by an influx of organic particles in core Ml 6. This layer is dated at 1912 in M5, 1937-1943 in core M16 and 1952-1955 in core Ml 1. This wide range is most likely related to uncertainties of the 210Pb chronology which increase with depth (J. Cornett, pers comm., 1997). This minerogenic influx may be associated with the 1946 earthquake. However, the lack of firm chronological control reduces the certainty of this assertion. The absence of this marker in cores Ml 1, M12, and M14 is attributed to reduced x-ray resolution (Appendix B). Trends in the 165 magnetic susceptibility of core M9 and its length suggest that the depth at which the layer should be seen has not been reached. 6.4.2. The Period 1953-1961 An increase in sediment yield is observed in the subsequent period 1953-1961 (Zone M-B) which is greater in the watershed of Maggie Lake than in the still unlogged watershed of Kite Lake. This suggests that the increase in sediment yield to Maggie lake exceeds the regional yield increase. Investigation of the origin of this local increase in yield suggest several possibilities. As mentioned previously, the pronounced nature of the peak in magnetic susceptibility is most likely related to the mining of iron ore upstream of Maggie Lake. In addition, however, this sedimentary zone coincides with two other catchment disturbances: Hurricane Freda and the onset of logging in the Maggie Lake watershed. Mass movement, and sediment mobilization most likely occurred as a result of Hurricane Freda. Logging was particularly extensive along Draw Creek just North of the lake in this period. The proximity of the creek would most likely ensure rapid transfer of sediments exposed as a result of clear-cutting and mobilized as a result of rainstorm events. In addition, road construction, which is known to be a significant factor in accelerated erosion of surface materials, was probably extensive in this early period of forestry activity. As a result, it is plausible to infer that both of these disturbances also contributed to the recorded change in lacustrine sedimentation. The relative importance of these three disturbances in influencing the sedimentation response is difficult to assess. However, the difference in the end of the maximum in magnetic susceptibility (1969 in core M5 and 1977 in core M16) may be a reflection of spatial variability in 166 the relative influence of logging and mining activity. Core M5 is located in the upper basin and thereby most likely to have been influenced by the operation of the mine. Core Ml 6 is located near the Paradise Creek inflow. Large areas immediately North of Paradise Creek and on the western edge of the Maggie watershed drained by Paradise Creek were logged in the seventies and early sixties respectively (Fig. 4.6). It is therefore possible that core Ml 6 was more sensitive to ongoing effects of logging in that part of the basin, while the properties of core M5 reflect the closure of the mine in 1969. Instances of localized influxes in organic matter are superimposed on this general trend. A discrete organic rich layer results in the asymmetry of the low in the organic content of core M12. As this layer is also identifiable in core Ml 1, an erosional event in the gully on the adjacent hillslope which is directly in line with these two cores may be the origin of this organic influx (Figs. 4.7, 4.16). Other similar events are noted in cores M4, M17 and M14. The organic rich layer in Core M4 may be related to the 1955 logging which occurred just north of Maggie Lake along the eastern inflowing creek. The absence of a similar layer in cores M2 and M3 which are more in line with Draw Creek's inflow supports this inference. The high in organic content is sustained for two thirds of this period. However, it is difficult to say how quickly this layer was deposited and if the response was quick or prolonged following upstream disturbance. Changes in sediment properties suggest a much higher influx of clastic sediments, in general, as well as a much higher influx of magnetite-rich sediments in particular. This is evident from the darker (more dense) grey tone, bulk density, a pronounced peak in magnetic susceptibility, and an increase in coarse and medium silt concentrations. Conversely, organic matter is low during this period. The assemblage of elements which increase (Si, Mg, Cr, Cu and Ni) in this zone are likely to be associated with a new source of sediment. These general changes 167 in sediment properties are consistent with the change in clastic sediment yield and may therefore suggest that catchment disturbances are predominantly recorded as a change in the minerogenic fraction of the sediment. 6.4.3. The Period 1961-1979 The initial increase in sediment yield recorded in Zone M-B is not sustained through Zone M-C, despite a continued regional increase and intensive logging in the late sixties and early seventies (Fig. 4.6). In light of regional trends, the lack of increase in sediment yield suggests that much of the material available and mobilized throughout the watershed is not reaching the lake. A sediment yield decrease in this period may be explained in several ways: an increase in upstream storage, and/or a reduction in the effect of upstream disturbance. Possible areas of storage are the floodplains of Draw Creek and Paradise Creek. However, it is hard to explain a change in upstream storage over this short time scale. The effects of forestry activity in the earlier period may have been more severe than in this period. In addition, during this period, logging moved onto higher slopes and away from the streambanks of creeks in the valley. Construction of roads in the early years may have been more extensive. The actual decrease in yield despite a regional increase in sediment yield suggests that upstream storage is more significant in the catchment of Maggie Lake. Several localized events are recorded during this period, notably a minerogenic layer in core M4 at the upstream end of the lake and two organic rich layers in core Ml 1. The older of the two layers in Ml 1 (1975-1979) may be the result of timber harvesting above the gullies in the late sixties and early seventies. While the apparent lag may be a function of the uncertainty associated with the dating of this relatively disturbed core, it may support the notion of lag where 168 slow root deterioration delays slope failure following harvesting. The second and most recent event layer observed in Ml 1(1987-1991) coincides with the logging of a cut block right above the lake and with a reported failure along this gully in 1986 (Fig. 4.7; Flip Wilson, MacMillan Bloedel, pers.comm., 1997). From 1961 to 1979, sediment properties of Zone M-C show a return to relatively stable conditions. The magnetite-rich fraction of clastic sediments remains high compared to Zone M-A, as evident from the slightly higher values of magnetic susceptibility. The stability of the clastic component is supported by the sustained darker grey tone. Thus while increases in sediment yield are not sustained throughout this period, sediments continue to bear the imprint of a higher clastic fraction. This may be due to the continued erosion of magnetite-rich sediments associated with the mine. 6.4.4. The period 1979-1997 Increasingly remote forestry activity, and improved harvesting practices post-19%0 may explain the continued decrease in sediment yield. It is hard to assess how this is related to the regional trend, as the only comparison for this period is the slight decrease in sediment yield identified in Clayoquot Lake over a much longer time span. A local event layer in core M9 in the upper section of M-D (1979-1997) is likely to be related to timber harvesting which took place adjacent to the lake in the late eighties. Core M9 is in line with Gully 3 which has since been repeatedly active and where mass movement was observed, most recently, this past autumn (Fig. 4.16; Flip Wilson and Karen Halwas, pers.comm., 1997). Zone M-D (1979-1997) shows a renewed increase in the influx of organic matter and 169 sustained inorganic influx which is higher than that of zone M-A (pre 1953). This is supported by magnetic susceptibility, the dark grey tone, an increase in sand and fine silt, and a rising trend in organic content over this period. These changes in sediment properties coincide with ongoing forestry activity. Decreasing elemental concentrations of Na, K and Mn after 1979 suggest that these elements are associated with a different source than before when these elements were strongly associated with organic matter. Their decrease however in a period when the clastic/magnetite-rich component of sediment remains high is surprising. Mackereth (1966) had postulated that the concentration of these elements in lake sediments would increase during periods of erosion as soils undergoing accelerated erosion would not have experienced as much leaching of these elements. Although there have been some qualifications, most work to date supports and expands on work initiated by Mackereth's study of England's Lake District. Through a study of Moraine Lake and Lake Hope Simpson in Labrador, Engstrom and Wright (1984) argue that Mackereth (1966) ignored the non-mineral fraction of inorganics as well as the biogenic and carbonate fraction of the ash weight left after loss on ignition. Dilution of Na and K by non-mineral inorganics is greatest in highly organic sediment and least in the more minerogenic sediments. This is due to the correlation between high autogenic organic production and diatom silica production (Engstrom and Wright, 1984). Thus, according to this work, a decrease in Na and K can be explained by two different interpretations. Increased stability of soil may lead to increased leaching of these two elements and their subsequent decrease in lake elastics, or an increase in biosiliceous or carbonate influx may dilute the otherwise constant minerogenic composition of the sediment. Both explanations are possible for the observed trend in Zone M-D. Historical records 170 show that logging activity in the eighties moved to areas farther away from the two main creeks draining the watershed (see Fig. 4.6). Road construction was most likely limited to these new areas of harvesting. Logging in the 1990s has been minimal. As a result, greater soil stability, especially in the lower elevation areas, may have characterized this period in contrast to the heavy logging period of the sixties and seventies. In addition, biogenic silica, carbonate content and organic matter increased from the previous period (Appendices C and D). Thus, the apparent decrease in Na, K, and Mn may also be due to dilution by these other sediment fractions. 6.4.5. Sediment Source The identification of source based on magnetic properties is limited in this watershed. Spatial variability in the SIRM/Xo ratio of lake sediments exceeds downcore variability making any interpretation of changes in sediment source over time impossible. This spatial variability may be a result of the sensitivity of this parameter to small changes in sediment source from one core location to another and to various localized event layers found in several of the cores. The dominant source can be identified on the basis of the magnitude of the SIRM/Xo ratio throughout the core. The average SIRM/Xo of the lake sediments (13 ± 3 kArn1) corresponds to the average SIRM/Xo of soils and unconsolidated sediments (14± 4 kAm-1), standing in contrast to the much lower values associated with most bedrock collected in the watershed and with the much higher value of clay. Soil and till are not distinguishable. Soil on till and soil on bedrock have similar values (14 ± 5 kAm-1 and 14 ±2 kAm-1) thereby making a distinction between these two sediment sources impossible. The lower average SIRM/Xo value found in this lake compared to those found in Kite and Clayoquot may be related to the greater abundance of soils and unconsolidated sediments in the 171 watershed of Maggie Lake. It could also indicate that erosion of soils and unconsolidated sediments is more severe than in the other two catchments. A combination of these two explanations is likely. 6.5. CROSS-LAKE COMPARISON Changes in catchment conditions are recorded in different ways in the sediment records of the two logged basins. The increase in sediment yield corresponding to the period of logging in Kite Lake is higher than the initial increase related to forestry in Maggie Lake (1.6 vs 1.4). This is particularly significant considering the much smaller extent of forestry activity in the watershed of Kite Lake (Table 4.2, Figs. 4.6, 4.12) and the likely magnification of the signature of forestry activity in Maggie Lake from the occurrence of other catchment disturbances. This implies that there may be a better connection between sediment source and sink in the Kite Lake sediment cascade than in the Maggie Lake watershed. In addition, forestry activity in the watershed of Kite Lake may have been more disruptive and intensive over this short period of time. The lack of delay between disturbance and both the initial response in Maggie Lake and the response in Kite Lake is consistent with the nature of the sediment cascade in the relatively steep and humid conditions of the outer west coast of Vancouver Island. In both logged basins, changes in sediment properties coincide with the historical records of disturbance. In Maggie Lake, changes are recorded in the minerogenic fraction coinciding with disturbances from mining and forestry activity as well as Hurricane Freda. The change is most readily seen in the consistent pattern observed in the x-ray stratigraphy which shows a change from light to darker (denser) grey tone corresponding to 1953. In Kite Lake, an increase in the clastic fraction of the sediment corresponds with changes in catchment conditions during the 172 1990s. Discrete changes in sediment properties found in both records are particularly well correlated with documented records of forestry related disturbance. 6.6. METHODOLOGICAL DISCUSSION 6.6.1. Ideal Lakes and the Failure of Toquart Lake The selection of lakes considered in this study was based on criteria which optimized conditions for the preservation of high resolution sediment records (See section 3.2.2). Toquart Lake fulfilled the morphometric requirements of the ideal lake, having a simple morphometry, deep basins and steep sides. Although not relatively high, its trap efficiency is similar to that of Kite Lake where a sediment record of change in the last 160 years was successfully retrieved. One of the other criteria is a high sedimentation rate. This cannot be assessed without some reconnaissance coring and preliminary dating. While the chronological control in the Toquart master cores was not clearly established, one can infer that the sedimentation rate was very low from the rapid decrease in both 210Pb and 137Cs activity. This in and of itself, makes Toquart Lake inappropriate for the current study. It is worth considering what factors contribute to this low sedimentation rate so as to refine the selection criteria for future studies of this kind. A low sedimentation rate may have been inferred from consideration of areas of storage upstream of the lake. The Toquart basin is characterized by two u-shaped valleys where debris flow fans are common at the base of tributary valleys. While much of the coarser material coming from hillslopes may be stored in these fans, fine sediments may still be mobilized by the two main contributing creeks which flow along the base of these fans. Further down valley and just above Toquart Lake, however, lies an extensive 173 floodplain which has accumulated over the Quaternary period (Bruce Thomson, pers.comm, 1997). This may be a storage point for finer sediment mobilized upstream. The dominance of Granitic Intrusions, which are more resistant than dominant bedrock types found in the other basins, could also explain the low sediment accumulation rates in Toquart Lake. Geology and the potential for upstream storage based on a basin's geomorphology may be additional characteristics to consider in the lake selection process. 6.6.2. Coring Density and Spatial Variability The coring density adopted adequately captures the spatial variability in sediment deposition. While the sediment record of Maggie Lake is complex, recording incidences of localized events in many of the cores, a general pattern is still discernible allowing lake-wide interpretations of changes in sediment properties and sediment yield to be made. The relative simplicity of the Clayoquot record still shows enough variability in sediment properties to define three lake-wide sedimentary zones. The lack of cross-core consistency in Kite Lake is attributed to the large component of organic matter which made the retrieval of long cores difficult. This was especially true at the upstream end of the lake where "organic trash layers" were repeatedly encountered. While the use of a single core for the interpretation of change is not optimal, the central location of core K2 and the simple bathymetry of Kite Lake, lends some confidence to the claim for the representative nature of that core. The assessment of spatial variability however is limited. The calculation of catchment sediment yield involves the extrapolation of accumulation rates in dated master cores to the rest of the lake. The spatial variability demonstrated above needs to be incorporated into this calculation. The method adopted in the current study 174 demonstrates the importance of using multiple cores in calculating whole lake sediment accumulation. The mass sediment accumulation rates for the sedimentary zones of the three master cores in Maggie Lake are not representative of the mass sediment accumulation rates in other cores across the lake. This is shown through a comparison of the zonal sediment accumulation rates in the master cores with the zone's average accumulation calculated from multiple cores. It is also evident from the large standard deviation associated with the average zonal accumulation rates based on multiple cores (Table 6.1, Appendix G for complete data set). Similar patterns are seen in the sediment accumulation rates of the master core CI and the associated zonal average based on all Clayoquot cores (Appendix G). The implications of this finding are illustrated in the following example. Calculation of whole lake accumulation in Zone M-B based on the average rate observed in the three master cores would yield a sediment accumulation for the whole lake 40% higher than the one calculated using 14 cores. The same calculation for Zone M-A would yield a whole lake accumulation that is 65% lower than the one calculated using 12 cores. Sediment yield would be reported to increase by a factor of 2.8 between the period covered by Zone M-A to that covered by Zone M-B. Sediment yield in Zone M-B using the multiple core approach was only 1.4 times higher than the sediment yield of Zone M-A. The use of a single core would have suggested that the effects of catchment disturbance were twice as high. Clearly, this has implications for future studies: multiple cores are essential in assessing catchment sediment yield from lake sedimentary records. The lake-sediment approach should not be used on a large scale using single cores from many lakes. A relatively detailed analysis using multiple cores is required in order to take into account the effect of spatial variability in sediment deposition. 175 Table 6.1: Comparison of mass sediment accumulation (MSA) of master cores with the average ised on t le MSA in multi pie cores (see Ap pendix G for full data set). Zone M5-MSA (t) M16-MSA (t) Mll-MSA(t) Avg ± std MSA (t) (# of cores used) M-D 2777 3436 n/a 3436 ±1672 (15) M-C 3178 4033 4693 5026 ±2151 (15) M-B 5446 5469 4089 3545±1795 (14) M-A 1399 3554 3232 3826 ±1702 (12) 6.6.3. Relevant Sediment Properties The two properties which appeared to be most sensitive to catchment change were organic content and magnetic susceptibility. These two properties are easily measured and provide the means to assess changes in sediment composition, a property which is likely to be sensitive to forestry-related catchment disturbance. While other studies of sediment yield and surface erosion have focused on the minerogenic component of the sediment fraction, the current study shows that catchment disturbance is also reflected in fluctuations of organic content. Other useful analyses include x-radiography to establish stratigraphy and the SIRM/Xo ratio to establish sediment source. X-ray images proved to be indispensable in establishing cross-core correlations and in determining the stratigraphy of the cores due to the visually indistinct nature of the sediment. This will be true for other lakes with highly saturated organic rich sediment. The measurements to establish the SIRM/Xo ratio are not only rapid and non-176 destructive, but the results can also lead to the identification of sediment source. Other properties such as particle size and geochemistry require more technical expertise to establish. The complexity of the controls on sediment geochemistry present additional challenges in the interpretation of these data. Bulk density, biogenic silica and carbonate content are required for the calculation of sediment yield. A sampling interval of two centimetres was deemed adequate to characterize the downcore variability of biogenic silica and carbonate content. While the lack of variation in these two parameters may be a function of the time scale of this study, autogenic sedimentation may be more variable in other lakes, requiring measurement at a higher resolution. Moisture content did not provide any additional information due to its high degree of correlation with other parameters. Menounos (1997) has shown that this very correlation can be used to estimate bulk density and organic content indirectly at much higher resolution than would otherwise be possible. This is an area that could be explored especially for cases like Toquart Lake where low sedimentation rates reduce the resolution of the sedimentary record. 6.6.4. Sensitivity to Change and the Lake-sediment Approach One of the main research objectives was to assess the adequacy of a sedimentological study for the purpose of monitoring the effects of forestry activity. The suitability of the lake sediment approach rests largely on the degree of chronological control established. The limitations and constraints of the dating techniques have been discussed and reinforce the need to use as many lines of evidence as possible. Thus, while the use of two dating techniques can provide a check on the precision of either technique, the assessment of the bias requires other lines of evidence such as the occurrence of regional marker layers and local chronological markers 177 such as the magnetic signature associated with mining in Maggie Lake. The paired-catchment design is essential in the interpretation of the sediment record to distinguish between local (and possibly forestry activity-related) changes in sediment yield and those associated with regional environmental variability. This approach was relatively successful except for lack of regional sediment yield data for the period of 1978 to the present. While using the change in the sediment yield of Clayoquot Lake after 1963 gave a sense of the regional trend over this period, higher resolution of regional fluctuations since 1963 would have been preferable. In this respect, the use of Kite Lake as an additional paired- catchment proved invaluable. Chapter 7 Conclusions and Recommendations 178 7.1. SUMMARY OF FINDINGS The current study has documented changes in lacustrine sedimentation that coincide with catchment disturbance. Comparison of the sediment record of disturbed catchments with the sediment record of unlogged or pre-logged control catchments has shown that significant increases in sediment yield related to forestry activity were recorded. In Maggie Lake, the increase in sediment yield is plausibly related to three different types of catchment disturbances: mining activity, Hurricane Freda and the onset of forestry activity. In Kite Lake, increases in sediment yield since 1988 are inferred to be related to the onset of forestry. The initial increase in sediment yield recorded in Maggie Lake is not sustained from 1961 to 1979 despite ongoing catchment disturbance associated with forestry activity and despite a regional increase in sediment yield. This may be indicative of reduced road construction and timber harvesting being carried out further away from the lake and contributing creeks. The decrease in sediment yield despite regional increases is indicative of the importance of storage upstream of Maggie Lake. The continuation of this pattern from 1979 to the present may be attributed to the above reasons as well as to the improvement of timber harvesting practices, which were particularly significant in the eighties. In summary, the initial increase of sediment accumulation in Kite Lake can plausibly be attributed to the forestry activity in that catchment. In contrast, other catchment disturbances in the Maggie Lake watershed confound the record, making the assessment of forestry effects on lake sedimentation more difficult. Event marker layers were identified in the sediment record of Clayoquot Lake, Kite Lake 179 and Maggie Lake. Comparison with the history of disturbance in these catchments indicated that some of these markers may be related to historic natural landslides and to timber harvesting effects in the immediate area surrounding the lakes. Lastly, temporal changes in sediment properties were assessed in the light of catchment disturbance. This analysis revealed that the increase in the relative importance of the minerogenic fraction in general, and the magnetite-rich fraction of the sediment, in particular, coincided with catchment disturbance. Whereas this sedimentary signature in the sediment record of Maggie Lake is significantly influenced by the mining of iron-ore, it is also well defined in the sediment records of Clayoquot and Kite lakes. Organic content is sensitive to changes in upstream catchment conditions, showing a general increase in the post 1953 period at Maggie Lake. Moreover, influxes of organic matter were related to specific depositional events in all three lakes. X-radiography also appears to contribute a sensitive record of catchment disturbance history by changes in the general pattern of grey scale densities as well as by delineating event markers. Thus, both general changes in sediment properties and spatially localized responses to specific disturbance are apparent throughout the lake. The appropriateness of the approach to assess the effects of forestry activity depends significantly on the precision of chronological control. The interpretation of the sediment record is subject to the limitations and constraints of the sediment chronology imposed by the assumptions and uncertainties associated with the dating techniques. In the current study, the limitations and potential biases of two dating techniques were investigated. The isotopic record of 137Cs was shown to be particularly sensitive to downward mobility. In addition, the 210Pb dates are sensitive to two assumptions made in the modelling of 210Pb activity. One of the assumptions can lead to overestimates of sediment yield, while the other can lead to underestimates of 180 sediment yield. The wide range of the discrepancies encountered in the master cores of Maggie Lake, Kite Lake and Clayoquot Lake suggests that uncertainties stem from both assumptions. As a result, the need for additional evidence to assess the nature of the bias is emphasized. The inability to resolve changes in sedimentation in the Toquart Lake basin, demonstrates that geology and the potential for upstream storage must be considered as criteria in the selection of lakes suitable for the purpose of monitoring the effects of forestry activity. Appropriate characterization of spatial variability is essential to establish the magnitude of temporal change in whole lake sediment accumulation and catchment sediment yield. The method used in the current study allowed consideration of the spatial variability in sediment accumulation across the lake and showed that use of single cores in sediment yield calculations results in erroneous estimates of catchment changes. 7.2. RECOMMENDATIONS FOR FUTURE WORK Several aspects of the current work could be explored further. The history of catchment disturbance could be refined in the case of Kite Lake where historical records of natural disturbance coinciding with forestry-related disturbance are scarce. More recent air photos would facilitate this reconstruction of natural disturbance. The current study revealed that organic content was one of the sediment properties sensitive to catchment change. Catchment sediment yields were calculated on an organic content-free basis. Estimates of organic sediment yield over time may give further insight into the nature of the lacustrine sedimentation response to catchment disturbance. Additional sensitivity analysis of the chronological data similar to that carried out for core T10 may give a more refined understanding of the potential bias of the dating techniques. As the 181 establishment of a chronology of sedimentation is key to the success of this approach, future work should focus on resolving problems associated with dating techniques. The current study has placed particular emphasis on the relative change in sediment yield over time. The absolute magnitude of the sediment yield data recorded has largely been ignored. Future work could investigate this further and assess the relation between catchment sediment yield recorded in the lake and catchment sediment yield estimates based on terrestrial evidence of erosion. This would provide a measure of how much sediment mobilized by disturbance is actually reaching downstream sinks such as lakes. The role of upstream storage in mediating the lacustrine sediment response to upstream effects of forestry activity could then be more fully explored. Future use of the lake-sediment approach to monitor the effects of forestry activity need to consider the possibility of low sedimentation rates and consequent resolution of the sediment record obtained from a particular lake, the limited quantity of sediment available for analysis of near-contemporaneous catchment change, the spatial variability in sedimentation, and the potential bias of the adopted chronology. The possibility of low sedimentation rates may be inferred from consideration of the bedrock geology as well as the extent of upstream storage areas. The subsampling strategy of the sediment record must be rigorously defined prior to the commencement of analyses to ensure that sediment properties are resolved as highly as possible. In addition, strategic use of available sediments is necessary to ensure that there is enough sediment for all analyses to be carried out. The spatial variability of sedimentation dictates a multiple-core approach in the calculation of whole-lake accumulation and catchment sediment yield. Even if they are centrally located in the depositional zone of a lake, single cores may not be representative of whole lake accumulation patterns. While a single core study design is both 182 faster and cheaper, its use is strongly discouraged as the results obtained and the subsequent interpretation of the effects of catchment disturbance may be completely incorrect. 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G. and Robinson, M. 1993. Experimental basin studies - an international and historical perspective of forest impacts. Journal of Hydrology 145: 217-230. Williams, H. F. L. and Hamilton, T. S. 1995. Sedimentary dynamics of an eroding tidal marsh derived from stratigraphic records of Cs-137 fallout, Fraser Delta, British Columbia, Canada. Journal of Coastal Research 11(4): 1145-1156. Wise, S. M. 1980. Caesium-137 and lead-210: a review of the techniques and some applications in geomorphology. In Timescales in Geomorphology. Cullingford, R. A.;Davidson, D. A. and Lewin, J., (eds.). Chichester: John Wiley and sons: 109-127. Appendix A Precipitation data 192 Monthly Total Precipitation, Tofino, Vancouver Island for the period of 1942-1991 (Canadian Climate Data, Environment Canada). Monthly Precipitation, Ucluelet-Kennedy Camp, Vancouver Island for the period of 1957-1997 (MacMillan Bloedel Limited, Kennedy Estevan Divisions). All data are in millimeters 193 o CD Q o> 0 0 CO CO CO O) CO CO CN X - CM T - o> CO in CN O o> CD in CO T - t*- 0 0 oo CM oo CO O T - CO ' T CD CO X— CO 0 0 O) CM d oo oo d d CM d 0 0 CM CO iri ih d d CO t v ! iri CD x— CO CN in co r - CN r- 0 0 CO o X— v~ N- CN O) CM x— O O) o> 05 r - x— O) o m O) T CD oo o CO co oo co r » CO in 0 0 CM co in CM CO co CN CD x— CO CN co CO o CO co co CO CN CN CN CO CO CO CO CN CO CN CO CO CO CO CN CO CO CO co CO CO CN co CO CO CO CO CM CO CO CO CN CO CO •*r o O) T a> T CO CO CM CO CO 1^  in 05 o in ,_ CD O) in CO CO r~ CO CD CN *<r CD CO ^1- o in X—' in d CN CN CO d CO 0 0 T— in CO X ~ CO d d CD 0 0 0 0 CM oo CO CO CN CO CO 0 0 CO iri CM 7— CO CD r - co CN 0 0 x— oo in o 0 0 0 0 CO CN CD 0 0 CO o CO co o> oo 0 0 CD 0 0 X— CO in CN CO CN CO CN TJ" CO in CO CO CO in CO in CO CO CO » • CO CO co CN CO CO CM I f ) CO 05 05 CN at in CM o CO CO 0 0 co o CM CO O) 0 0 0 0 0 0 O) r - h- CO T oo CO h~ CO CO CN o CO CM CN o d 0 0 0 0 CN CO co CN in CO 0 0 d d oi iri d 0 0 CD •<r d CO CM CO d CO X™ CO d iri XT~ d d 1 0 o in CO T— o CN CO in in CD CO 0 0 CI 0 0 CD CN in CO CO 0 0 CO CM CO CN in CO CO CO h- in CO in CO CM in CN CO r - T— in CO in in CD m CO CN o CO CN o r- 0 0 CO CO 0 0 CO CT> 05 in X— CN o cn CN CD co CN CD CO o iri iri d d d d iri iri CM d d d d CO CN d d d d d d d >«r •<*•' CM CM d •«r T' CM o 05 CM o O) x— 0 0 in CD 0 0 CM 0 0 o o CO cn CO in cn o CO CD o CO O CD CO CN TT CD CN CM CM CM CM T in CN in CO oo r - CM CN in co CO h-CO CO CM CO T CO CD *™ *~ O CN in O CL CD CO CO °0 CO CD CO m CM co 0 0 O x— 0 0 m ^— co o x— x— o iri d d d d iri cn d CO d IT) d d cri d d CD CO CN v~ in o 0 0 in O o in o CN CN CM CN CN CN T— CO CM d d cn CO 1 - m T - CD CD CM 0 0 T— iri d d d d CD d d 05 T - CN CO T— o CN o CD CN 0 0 T— CO CM CO X - x— x CO CN -m d . m < ? 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8 CM CO T C CM in s Tf- O 00 00 T— s C N 8 C M 8 C M cri L O C O L O 00 C M C N cn C O C M L O C O L O 3 8 in C N SN h-C O C T C l D C D C D C O r ^ C n T - U I O T - Q O l O C n r ^ - C p Q Q T - C D C O C O t ^ T f T C C M , ^ CO iSTcr^ cocoo c^oc incocDOjinpcomcDCMQ co ^T-cnTcinr^inT-incMCD DinNcNTjcNt^TccoincNCMCM T C ! 8 C D | 3 D 195 Appendix 6 X-Radiographic Images of all cores Maggie Lake 196 Toquart Lake 204 Kite Lake 208 Clayoquot Lake 209 Note: -Positive prints were made from x-radiographs at different exposures to obtain optimum resolution. -See Fig. 4. 16 for core locations in Maggie Lake, Fig. 4.18 for core locations in Toquart Lake, Fig. 4.20 for core locations in Kite Lake, and Fig, 4.22 for core locations in Clayoquot Lake. 196 M3 M2 M4 Zone M-D 197 M17 198 M16 Zone M-D Zone M-D Zone M - C Z o n e M-B this lighter sect ion is probably an event layer like the one above rather than the change in grey tone observed in other cores-this is supported by trends in other sediment propert ies. 199 2 0 1 202 Z o n e M-D Base of Zone M-B in M13 was defined on the basis of organic content trends. It is slightly offset from the change in grey tone which characterizes the base of M-B in other cores. Zone M-D Zone M-C Zone M-B Zone M-A wood chip Evidence of both in-situ and extrusion disturbance on T5-this core was not analyzed further. 205 Zone T-D Zone T - C Zone T -B 207 208 209 Appendix C Basic Physical and Magnetic Properties Hygroscopic Moisture (%) Total Residual Moisture (%) Density (g cm"3) LOI (%) Magnetic Susceptibility (Xo) [x lO^Wkg"1] SIRM [Am'kg-1] SIRM/Xo [k Am"1] -The above properties are presented for all cores in: Maggie Lake Toquart Lake Kite Lake Clayoquot Lake -Depth is the mid-point depth of the layer sampled for the analysis. 211 M 1 core depth %hygro % Total density % LOI Xo SIRM ample [cm] moisture moisture [g/cm3] [E-06mA3/kg] [Am2kg-1] 1 0.55 2.7 62.9 0.292 16 1.54 0.0215 2 1.65 2.2 53.7 0.668 15 1.66 0.0235 3 2.75 2.2 53.0 0.715 14 1.64 0.0235 4 3.85 2.1 52.4 0.755 13 1.67 0.0233 5 4.95 1.9 49.6 0.794 13 1.67 0.0216 6 6.05 1.9 50.1 0.658 13 1.56 0.0099 7 7.15 1.9 50.4 0.860 13 1.72 0.0219 8 8.25 1.8 49.7 0.846 12 1.91 0.0247 9 9.35 1.7 48.2 0.801 11 2.63 0.0319 10 10.45 1.6 49.3 0.883 11 2.96 0.0374 SIRM/Xo [KAm-1] 14 14 14 14 13 6 13 13 12 13 M 2 M 3 1 0.55 2.6 63.0 0.496 15 1.75 0.0233 13 2 1.65 2.2 52.6 0.701 13 1.87 0.0208 11 3 2.75 1.8 49.6 0.740 11 1.90 0.0210 11 4 3.85 1.3 42.9 0.767 8 1.81 0.0156 9 5 4.95 1.7 46.7 0.872 10 1.85 0.0217 12 6 6.05 2.0 49.0 0.803 11 1.94 0.0217 11 7 7.15 2.1 48.9 0.778 11 1.92 0.0236 12 8 8.25 2.1 51.1 0.816 11 1.91 0.0240 13 9 9.35 2.0 49.7 0.744 11 2.01 0.0232 12 10 10.45 2.0 50.8 0.811 10 2.49 0.0301 12 11 11.55 1.9 51.2 0.786 10 2.85 0.0341 12 12 12.65 1.9 50.6 0.781 9 4.36 0.0587 13 13 13.75 1.6 48.1 0.794 8 3.75 0.0509 14 14 14.85 1.7 48.1 0.880 8 2.46 0.0326 13 15 15.95 1.3 44.7 0.885 8 1.76 0.0205 12 16 17.05 1.7 54.1 0.650 10 1.45 0.0173 12 17 18.15 1.7 55.1 0.672 10 1.40 0.0159 11 18 19.25 1.9 54.1 0.671 12 1.29 0.0133 10 19 20.35 1.9 56.9 0.595 12 1.18 0.0105 9 20 21.45 1.6 52.7 0.721 11 1.24 0.0095 8 21 22.55 1.1 35.3 1.073 7 1.27 0.0099 8 1 0.55 1.3 41.0 0.779 6 2.00 0.0155 8 2 1.65 0.9 36.5 1.095 6 2.17 0.0169 8 3 2.75 1.0 41.0 0.926 6 1.93 0.0150 8 4 3.85 1.1 40.3 0.955 6 1.92 0.0142 7 5 4.95 1.4 47.6 0.825 8 1.92 0.0170 9 6 6.05 1.5 47.6 0.784 9 1.91 0.0180 9 7 7.15 1.5 48.7 0.886 9 2.06 0.0216 10 8 8.25 1.9 48.6 0.817 10 2.04 0.0215 10 9 9.35 1.5 49.1 0.802 10 2.38 0.0260 11 10 10.45 1.5 49.5 0.819 9 3.15 0.0321 10 11 11.55 1.3 47.9 0.837 8 3.84 0.0439 11 12 12.65 1.1 44.0 1.050 7 3.05 0.0327 11 13 13.75 1.5 47.7 0.881 9 2.07 0.0232 11 14 14.85 1.7 53.7 0.717 11 1.47 0.0112 8 15 15.95 1.4 45.7 0.879 9 1.52 0.0103 7 16 17.05 1.5 46.6 0.831 10 1.58 0.0118 7 17 18.15 1.6 49.6 0.766 11 1.62 0.0111 7 18 19.25 2.3 56.2 0.616 18 1.52 0.0110 7 19 20.35 2.6 62.2 0.506 19 1.33 0.0103 8 20 21.45 2.5 62.3 0.485 16 1.47 0.0125 9 212 Core M4 M 5 core depth %hygro % Total density % LOI Xo SIRM SIRM/Xo ample [cm] moisture moisture [g/cm3] [E-06mA3/kg] [Am2kg-1] [KAm-1] 2 1.65 3.7 61.0 0.625 15 1.72 0.0246 14 3 2.75 3.4 54.6 0.794 13 1.76 0.0237 13 4 3.85 2.7 49.9 0.881 11 1.88 0.0220 12 5 4.95 2.1 49.7 0.891 10 1.80 0.0220 12 6 6.05 2.2 49.9 0.844 10 1.97 0.0237 12 7 7.15 2.2 51.4 0.862 11 1.93 0.0229 12 8 8.25 2.2 49.8 0.862 10 2.00 0.0227 11 9 9.35 1.7 45.4 1.034 8 2.10 0.0233 11 10 10.45 2.3 50.9 0.656 11 2.38 0.0298 13 11 11.55 2.1 51.7 0.848 11 2.47 0.0270 11 12 12.65 2.3 53.4 0.555 11 3.42 0.0377 11 13 13.75 1.8 50.5 0.893 9 4.62 0.0637 14 14 14.85 2.4 58.2 0.689 13 2.35 0.0180 8 15 15.95 2.3 56.9 0.773 13 2.34 0.0299 13 16 17.05 2.0 54.0 0.785 10 2.28 0.0321 14 17 18.15 2.0 55.5 0.748 11 1.73 0.0178 10 18 19.25 2.5 61.5 0.595 17 1.41 0.0144 10 19 20.35 3.2 65.9 0.494 26 1.19 0.0104 9 20 21.45 2.8 58.4 0.706 16 1.34 0.0146 11 21 22.55 1.8 51.8 0.859 11 1.48 0.0175 12 22 23.65 2.2 54.3 0.770 12 1.36 0.0158 12 2 1.65 2.6 59.4 0.564 15 1.76 0.0235 13 3 2.75 2.4 52.9 0.722 14 1.81 0.0243 13 4 3.85 2.1 53.7 0.637 14 1.79 0.0219 12 5 4.95 2.3 56.6 0.580 14 1.75 0.0208 12 6 6.05 2.6 54.0 0.639 12 1.78 0.0247 14 7 7.15 2.0 52.3 0.677 12 1.83 0.0247 14 8 8.25 1.9 52.6 0.647 12 1.84 0.0254 14 9 9.35 2.0 53.8 0.677 12 1.87 0.0246 13 10 10.45 2.2 53.2 0.672 11 2.03 0.0257 13 11 11.55 2.3 54.1 0.767 11 2.28 0.0307 13 12 12.65 2.2 53.3 0.758 11 2.75 0.0384 14 13 13.75 2.1 51.3 0.823 10 3.59 0.0498 14 14 14.85 1.9 52.0 0.784 9 5.07 0.0689 14 15 15.95 1.6 48.5 0.879 8 3.48 0.0437 13 16 17.05 1.6 46.8 0.899 8 2.87 0.0378 13 17 18.15 1.9 55.3 0.598 10 2.11 0.0260 12 18 19.25 1.7 50.0 0.713 9 1.66 0.0213 13 19 20.35 2.0 55.5 0.600 11 1.44 0.0184 13 20 21.45 2.5 60.2 0.661 14 1.35 0.0125 9 21 22.55 2.2 57.6 0.594 13 1.36 0.0158 12 22 23.65 1.8 53.4 0.663 12 1.46 0.0139 10 23 24.75 2.6 62.3 0.502 16 1.43 0.0177 12 213 Core M 7 core sample 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 depth [cm] 0.85 2.25 3.35 4.45 5.55 6.65 7.75 8.85 10.1 11.5 12.9 14.15 15.25 16.35 17.45 18.55 19.65 20.75 22 %hygro moisture 2.9 2.2 2.1 2.0 2.0 2.2 2.4 1.9 1.4 3.5 3.2 2.7 3.3 2.5 2.2 2.4 2.5 2.6 3.5 % Total moisture 2.9 58.6 57.4 57.2 53.3 56.2 57.7 54.7 46.2 63.6 64.2 62.6 63.2 60.6 58.4 57.4 55.8 59.3 62.2 density [g/cm3] n/a 0.646 0.749 0.826 0.887 0.896 0.805 0.836 0.958 0.632 0.642 0.588 0.692 0.774 0.766 0.699 0.707 0.689 0.859 % LOI 17 14 14 13 12 12 14 13 8 16 16 17 17 16 15 16 16 17 16 Xo [E-06mA3/kg] 1.28 1.42 1.60 2.03 2.55 2.20 1.57 1.59 1.88 1.57 1.64 1.49 1.44 1.49 1.53 1.57 1.50 1.53 1.63 SIRM [Am2kg-1] 0.0285 0.0306 0.0316 0.0380 0.0475 0.0346 0.0186 0.0118 0.0117 0.0179 0.0199 0.0189 0.0178 0.0193 0.0190 0.0186 0.0193 0.0214 0.0232 SIRM/Xo [KAm-1] 22 22 20 19 19 16 12 7 6 11 12 13 12 13 12 12 13 14 14 M 8 2 1.65 3.6 62.7 0.606 18 1.31 0.0177 14 3 2.75 4.0 62.7 0.613 19 1.32 0.0231 17 4 3.85 3.5 62.8 0.628 19 1.27 0.0153 12 5 4.95 3.4 61.2 0.499 18 1.50 0.0185 12 6 6.05 1.3 35.8 0.988 7 1.31 0.0100 8 7 7.15 3.0 62.1 0.561 13 1.33 0.0229 17 8 8.25 3.0 58.6 0.688 14 1.40 0.0284 20 9 9.35 3.0 57.3 0.708 14 1.56 0.0314 20 10 10.45 2.8 56.7 0.703 14 1.87 0.0364 19 11 11.55 2.9 56.4 0.744 13 2.42 0.0447 18 12 12.65 2.3 53.4 0.825 11 2.97 0.0550 19 13 13.75 2.0 55.1 0.696 12 1.99 0.0300 15 14 14.85 2.7 62.7 0.625 15 1.42 0.0204 14 15 15.95 2.6 63.3 0.572 17 1.30 0.0179 14 16 17.05 2.4 62.6 0.492 17 1.20 0.0121 10 17 18.15 2.6 62.8 0.584 16 1.34 0.0186 14 18 19.25 2.8 64.2 0.490 17 1.21 0.0178 15 19 20.35 2.8 67.1 0.464 17 1.26 0.0171 14 20 21.45 2.8 72.1 0.406 17 1.28 0.0159 12 21 22.55 2.7 70.8 0.443 18 1.31 0.0154 12 22 23.65 2.8 72.7 0.357 18 1.34 0.0146 11 23 24.75 2.7 65.1 0.418 17 1.46 0.0149 10 24 25.85 2.5 62.5 0.609 16 1.56 0.0141 9 214 core depth %hygro % Total density % LOI Xo SIRM SIRM/Xo sample [cm] moisture moisture [g/cm3] [E-06mA3/kg] [Am2kg-1] [KAm-1] 1 0.55 2.4 78.4 0.234 19 0.00 0.0000 0 2 1.65 1.8 61.5 0.595 17 1.29 0.0144 11 3 2.75 2.5 68.0 0.484 24 1.34 0.0163 10 4 3.85 2.0 62.5 0.531 18 1.44 0.0174 17 5 4.95 1.7 58.1 0.624 16 1.39 0.0155 11 6 6.05 1.7 60.5 0.584 16 1.42 0.0210 15 7 7.15 1.6 59.6 0.605 16 1.42 0.0187 13 8 8.25 1.4 56.7 0.643 14 1.54 0.0244 19 9 9.35 1.4 55.7 0.737 12 1.48 0.0229 15 10 10.45 1.5 57.1 0.639 13 1.56 0.0211 14 11 11.55 1.4 55.7 0.701 14 1.87 0.0265 18 12 12.65 1.2 53.5 0.700 13 2.58 0.0381 22 13 13.75 1.0 53.5 0.795 11 2.77 0.0386 15 14 14.85 1.0 51.5 0.773 12 2.16 0.0265 9 15 15.95 1.3 61.3 0.617 14 1.53 0.0167 7 16 17.05 1.1 58.3 0.676 13 1.27 0.0112 8 17 18.15 1.1 58.2 0.597 14 1.13 0.0092 7 18 19.25 1.3 60.5 0.644 16 1.05 0.0094 8 1 0.55 3.9 69.1 0.346 20 1.00 0.0143 14 2 1.65 4.4 67.5 0.389 24 1.19 0.0148 12 3 2.75 4.5 69.2 0.513 25 1.11 0.0155 14 4 3.85 4.3 68.1 0.437 25 1.13 0.0142 13 5 4.95 5.0 70.4 0.334 34 1.02 0.0121 12 6 6.05 3.7 62.3 0.451 22 1.18 0.0179 15 7 7.15 3.5 65.2 0.517 19 1.30 0.0251 19 8 8.25 3.5 65.4 0.503 20 1.36 0.0232 17 9 9.35 4.8 71.8 0.395 29 1.09 0.0164 15 10 10.45 4.3 70.6 0.389 27 1.18 0.0204 17 11 11.55 2.6 55.6 0.664 14 1.41 0.0269 19 12 12.65 2.7 57.6 0.646 14 1.83 0.0338 18 13 13.75 2.5 56.9 0.604 13 2.23 0.0400 18 14 14.85 2.2 57.4 0.647 13 2.91 0.0506 17 15 15.95 2.2 56.2 0.676 11 2.76 0.0494 18 16 17.05 3.1 65.4 0.465 18 1.52 0.0247 16 17 18.15 2.7 66.6 0.490 16 1.33 0.0221 17 18 19.25 2.5 62.1 0.576 15 1.26 0.0194 15 19 20.35 2.9 67.6 0.464 21 1.11 0.0164 15 20 21.45 3.1 68.0 0.458 19 1.04 0.0151 14 21 22.55 3.3 69.8 0.466 21 1.19 0.0167 14 22 23.65 3.1 67.2 0.479 21 1.19 0.0148 12 23 24.75 3.3 67.6 0.542 20 1.23 0.0168 14 24 25.85 3.1 66.0 0.547 20 1.29 0.0177 14 25 26.95 3.0 64.6 0.522 20 1.26 0.0176 14 215 Core core depth %hygro % Total density % LOI Xo SIRM SIRM/Xo sample [cm] moisture moisture [g/cm3] [E-06mA3/kg] [Am2kg-1] [KAm-1] 2 1.65 3.6 66.9 0.459 22 1.18 0.0190 16 3 2.75 3.6 65.9 0.456 24 1.30 0.0173 13 4 3.85 3.3 65.2 0.485 22 1.27 0.0185 15 5 4.95 3.0 62.9 0.587 17 1.35 0.0248 18 6 6.05 3.3 66.6 0.508 19 1.31 0.0236 18 7 7.15 2.9 59.0 0.531 17 1.40 0.0253 18 8 8.25 2.3 54.5 0.669 14 1.48 0.0273 18 9 9.35 2.2 57.2 0.636 14 1.64 0.0287 18 10 10.45 2.3 56.3 0.614 14 2.01 0.0000 0 11 11.55 2.4 55.8 0.670 14 2.31 0.0388 17 12 12.65 2.2 54.7 0.758 13 3.06 0.0516 17 13 13.75 2.0 55.9 0.750 12 2.74 0.0470 17 14 14.85 2.8 65.8 0.488 17 1.55 0.0264 17 15 15.95 2.6 60.3 0.601 16 1.34 0.0218 16 16 17.05 2.6 64.4 0.447 17 1.22 0.0191 16 17 18.15 2.8 66.6 0.489 19 1.12 0.0164 15 18 19.25 3.0 69.2 0.449 20 1.08 0.0147 14 19 20.35 3.0 68.2 0.415 20 1.12 0.0155 14 20 21.45 2.8 66.3 0.490 20 1.21 0.0172 14 21 22.55 2.9 67.7 0.398 20 1.23 0.0170 14 22 23.65 2.9 66.4 0.490 20 1.25 0.0177 14 23 24.75 4.0 67.2 0.530 19 1.29 0.0160 12 24 25.85 3.8 67.4 0.473 19 1.28 0.0164 13 25 26.95 4.0 68.1 0.507 20 1.28 0.0153 12 1 0.7 3.6 68.6 0.410 18 1.23 0.0149 12 2 1.95 2.9 55.7 0.683 15 1.35 0.0234 21 3 3.05 3.0 56.8 0.685 15 1.40 0.0263 19 4 4.15 2.9 56.8 0.659 15 1.43 0.0265 19 5 5.25 2.8 58.1 0.659 15 1.74 0.0321 23 6 6.35 2.7 56.6 0.657 14 2.28 0.0427 26 7 7.45 2.6 73.4 0.689 14 1.83 0.0327 14 8 8.55 2.7 61.4 0.619 15 1.29 0.0197 10 9 9.65 3.6 66.5 0.564 17 1.20 0.0165 12 10 10.75 2.8 65.3 0.560 16 1.17 0.0153 13 11 11.85 3.0 67.2 0.530 18 1.19 0.0165 15 12 12.95 3.1 69.6 0.487 19 1.19 0.0142 11 13 14.05 3.2 70.1 0.476 19 1.19 0.0164 14 14 15.15 3.1 70.9 0.452 19 1.19 0.0164 14 15 16.25 2.9 69.1 0.477 17 1.16 0.0146 13 16 17.35 2.9 67.4 0.494 17 1.18 0.0155 13 17 18.45 2.5 68.0 0.469 16 1.30 0.0189 16 18 19.7 1.8 66.8 0.493 15 1.75 0.0274 22 19 20.95 2.0 69.5 0.392 16 1.67 0.0273 16 20 22.05 2.0 70.4 0.500 16 1.51 0.0225 13 21 23.15 2.0 68.5 0.545 17 1.37 0.0222 15 216 core depth %hygro % Total density % LOI Xo SIRM SIRM/Xo sample [cm] moisture moisture [g/cm3] [E-06mA3/kg] [Am2kg-1] [KAm-1] 3 2.75 1.8 62.8 0.533 18 1.36 0.0246 18 4 3.85 1.4 59.1 0.638 16 1.48 0.0269 18 5 4.95 1.4 54.8 0.691 15 1.58 0.0276 17 6 6.05 1.4 55.4 0:678 14 1.60 0.0279 17 7 7.15 1.3 55.3 0.710 14 1.96 0.0330 17 8 8.25 1.2 53.9 0.672 13 2.77 0.0429 16 9 9.35 1.0 51.4 0.720 11 3.68 0.0577 16 10 10.45 3.3 56.7 0.667 12 2.64 0.0451 17 11 11.55 4.9 74.6 0.386 24 1.39 0.0217 16 12 12.65 4.8 72.4 0.428 23 1.16 0.0172 15 13 13.75 5.4 78.1 0.323 32 0.93 0.0126 13 14 14.85 3.0 77.8 0.291 15 0.77 0.0109 14 15 15.95 6.3 81.8 0.258 46 0.72 0.0102 14 16 17.05 6.4 81.9 0.282 41 0.77 0.0107 14 17 18.15 5.9 77.3 0.356 35 0.92 0.0138 15 18 19.25 3.0 62.1 0.545 16 1.38 0.0224 16 19 20.35 3.4 65.9 0.502 17 1.17 0.0166 14 20 21.45 3.5 65.9 0.506 18 1.16 0.0151 13 21 22.55 3.3 66.8 0.509 19 1.14 0.0143 13 22 23.65 3.5 67.0 0.528 19 1.13 0.0092 8 23 24.75 3.3 64.8 0.537 17 0.97 0.0103 11 24 25.85 3.6 68.0 0.439 19 0.97 0.0100 10 25 26.95 3.4 67.4 0.455 18 1.02 0.0111 11 26 28.05 3.3 67.0 0.460 18 1.12 0.0144 13 27 29.15 3.6 70.6 0.391 20 1.19 0.0156 13 1 0.55 3.5 74.8 0.313 20 0.78 0.0107 14 2 1.65 2.8 58.3 0.657 17 1.50 0.0262 17 3 2.75 2.5 55.7 0.639 15 1.52 0.0260 17 4 3.85 2.3 53.3 0.715 14 1.56 0.0267 17 5 4.95 2.0 50.6 0.759 13 1.59 0.0267 17 6 6.05 2.0 52.2 0.730 13 1.78 0.0289 16 7 7.15 2.6 52.0 0.790 12 2.02 0.0324 16 8 8.25 2.5 53.3 0.737 13 2.44 0.0377 15 9 9.35 2.5 51.9 0.796 12 3.72 0.0584 16 10 10.45 2.0 47.4 0.868 10 2.85 0.0445 16 11 11.55 2.5 55.0 0.705 13 1.94 0.0311 16 12 12.65 2.6 55.5 0.725 14 1.47 0.0226 15 13 13.75 2.7 58.3 0.679 15 1.23 0.0186 15 14 14.85 9.2 72.5 0.426 68 0.78 0.0103 13 15 15.95 1.9 63.9 0.553 14 0.67 0.0084 12 16 17.05 3.1 62.7 0.564 20 1.09 0.0148 14 217 core depth %hygro % Total density % LOI Xo SIRM SIRM/Xo sample [cm] moisture moisture [g/cm3] [E-06mA3/kg] [Am2kg-1] [KAm-1] 2 1.65 2.8 61.1 0.587 15 1.55 0.0235 15 3 2.75 2.5 56.0 0.763 13 1.61 0.0244 15 4 3.85 2.4 52.4 0.603 13 1.64 0.0249 15 5 4.95 2.3 53.8 0.821 13 1.63 0.0247 15 6 6.05 2.0 53.0 0.854 13 1.61 0.0240 15 7 7.15 2.0 53.5 0.802 13 1.93 0.0261 14 8 8.25 2.1 54.9 0.790 13 2.46 0.0311 13 9 9.35 2.1 53.6 0.813 12 2.87 0.0325 11 10 10.45 2.0 54.2 0.762 12 3.11 0.0394 13 11 11.55 1.6 47.8 0.956 10 3.43 0.0444 13 12 12.65 1.9 53.7 0.851 11 2.10 0.0321 15 13 13.75 1.9 55.9 0.742 13 1.39 0.0174 13 14 14.85 2.3 60.1 0.670 16 1.16 0.0132 11 15 15.95 2.3 64.0 0.587 16 1.08 0.0127 12 16 17.05 2.7 67.1 0.529 21 0.88 0.0091 10 17 18.15 2.0 60.6 0.640 16 1.05 0.0123 12 18 19.25 2.5 64.2 0.583 18 1.34 0.0166 12 19 20.35 3.5 62.1 0.435 17 1.34 0.0161 12 20 21.45 3.5 62.9 0.472 17 1.30 0.0138 11 21 22.55 3.4 63.7 0.454 18 1.25 0.0129 10 22 23.65 3.4 65.5 0.537 18 1.22 0.0151 12 23 24.75 3.4 64.9 0.572 19 1.23 0.0158 13 24 25.85 3.5 64.3 0.605 16 1.35 0.0169 13 2 1.65 2.9 56.0 0.711 17 1.55 0.0204 13 3 2.75 2.3 51.7 0.757 13 1.53 0.0189 12 4 3.85 2.4 52.4 0.797 13 1.62 0.0203 13 5 4.95 2.1 52.4 0.750 11 1.62 0.0195 12 6 6.05 1.9 49.9 0.791 12 1.53 0.0183 12 7 7.15 1.8 48.8 0.919 12 1.56 0.0176 11 8 8.25 2.0 53.5 0.686 13 1.36 0.0148 11 9 9.35 2.0 54.4 0.745 14 1.37 0.0166 12 10 10.45 2.0 50.9 0.747 13 1.48 0.0188 13 11 11.55 1.8 51.6 0.731 13 1.46 0.0158 11 12 12.65 1.8 50.9 0.863 12 1.60 0.0182 11 13 13.75 1.8 50.5 0.849 10 1.76 0.0208 12 14 14.85 1.8 51.3 0.833 12 1.96 0.0221 11 15 15.95 1.7 52.4 0.804 10 2.47 0.0289 12 16 17.05 2.1 65.9 0.555 14 2.36 0.0274 12 17 18.15 2.1 54.9 0.797 12 2.83 0.0331 12 18 19.25 1.7 48.2 0.922 9 3.87 0.0479 12 19 20.35 1.5 45.3 0.976 8 3.27 0.0422 13 20 21.45 2.1 61.7 0.559 13 2.13 0.0272 13 core depth %hygro % Total density sample [cm] moisture moisture [g/cm3] 2 1.65 2.4 52.7 0.652 3 2.75 2.6 50.7 0.653 4 3.85 2.5 53.0 0.633 5 4.95 2.0 50.2 0.847 6 6.05 1.9 49.0 0.851 7 7.15 2.1 50.3 0.814 8 8.25 2.0 51.1 0.861 9 9.35 2.0 52.2 0.830 10 10.45 2.0 51.8 0.875 11 11.55 1.7 49.4 0.886 12 12.65 1.5 46.4 0.930 13 13.75 1.3 43.6 0.787 14 14.85 1.4 46.3 0.671 15 15.95 1.6 52.0 0.804 16 17.05 2.0 56.6 0.594 17 18.15 2.0 58.2 0.667 18 19.25 2.5 60.0 0.459 19 20.35 2.4 60.5 0.457 20 21.45 2.1 57.9 0.526 21 22.55 2.7 62.3 0.425 22 23.65 2.4 61.7 0.541 23 24.75 2.3 59.3 0.473 %LOI Xo SIRM SIRM/Xo [E-06mA3/kg] [Am2kg-1] [KAm-1] 15 1.96 0.0247 13 13 1.87 0.0234 13 14 1.85 0.0239 13 12 1.90 0.0231 12 11 1.96 0.0251 13 11 1.92 0.0222 12 11 2.10 0.0249 12 11 2.72 0.0316 12 10 3.62 0.0380 10 9 5.09 0.0617 12 8 4.48 0.0548 12 7 3.06 0.0374 12 8 2.41 0.0292 12 10 1.61 0.0182 11 13 1.44 0.0162 11 13 1.42 0.0160 11 15 1.34 0.0140 10 15 1.60 0.0125 8 13 1.43 0.0141 10 17 1.50 0.0152 10 15 1.50 0.0160 11 16 1.47 0.0154 10 219 Core core depth sample [cm] T1 2 1.65 3 2.75 4 3.85 5 4.95 6 6.05 7 7.15 8 8.25 9 9.35 10 10.45 11 11.55 12 12.65 %hygro % Total moisture moisture density % LOI [g/cm3] 2.8 3.4 3.2 3.2 3.4 3.4 3.0 2.8 3.1 3.0 3.2 66.1 64.9 64.5 66.5 70.6 70.2 67.5 63.5 65.9 66.5 78.4 0.476 0.543 0.507 0.479 0.386 0.430 0.451 0.546 0.492 0.499 0.340 23 21 20 20 22 22 20 16 19 19 21 Xo [E-6m3/kg] 1.03 1.02 1.12 1.08 1.01 1.02 0.95 0.97 1.00 0.96 0.89 SIRM SIRM/Xo [Am2kg-1] [KAm-1] 0.0229 22 22 0.0229 0.0231 0.0227 0.0197 0.0215 0.0196 0.0179 0.0192 0.0178 0.0174 21 21 19 21 21 18 19 19 20 T2 T3 T4 2 1.65 2.4 61.7 0.612 18 1.24 0.0347 28 3 2.75 2.2 61.0 0.611 18 1.24 0.0332 27 4 3.85 2.6 67.2 0.476 21 1.19 0.0313 26 5 4.95 2.5 67.1 0.511 20 1.17 0.0292 25 6 6.05 2.2 64.0 0.575 19 1.12 0.0259 23 7 7.15 2.4 65.3 0.575 18 1.14 0.0274 24 8 8.25 2.7 66.6 0.499 18 1.19 0.0288 24 9 9.35 2.8 67.4 0.520 19 1.18 0.0278 24 10 10.45 2.7 65.3 0.509 18 1.18 0.0267 23 11 11.55 2.6 65.7 0.510 18 1.12 0.0248 22 12 12.65 2.6 65.2 0.524 18 1.11 0.0240 22 13 13.75 2.4 63.3 0.550 17 1.06 0.0188 18 14 14.85 2.6 62.7 0.551 17 1.02 0.0207 20 15 15.95 2.6 63.3 0.568 17 0.95 0.0197 21 16 17.05 2.8 64.3 0.533 18 0.87 0.0175 20 2 1.65 2.7 61.0 0.581 18 1.17 0.0297 25 3 2.75 2.5 61.1 0.611 17 1.20 0.0259 21 4 3.85 3.0 66.1 0.492 20 1.08 0.0256 24 5 4.95 2.9 66.3 0.524 19 1.08 0.0257 24 6 6.05 2.7 63.8 0.544 18 1.03 0.0232 23 7 7.15 2.6 63.8 0.558 18 1.06 0.0235 22 8 8.25 2.4 63.1 0.552 18 1.11 0.0248 22 9 9.35 2.6 63.1 0.591 18 1.11 0.0245 22 10 10.45 2.5 63.3 0.556 18 1.02 0.0206 20 11 11.55 2.7 63.0 0.577 18 1.02 0.0214 21 12 12.65 2.4 61.6 0.624 17 1.40 0.0199 14 2 1.65 3.5 69.0 0.382 31 1.08 0.0208 19 3 2.75 2.9 65.0 0.431 23 1.01 0.0179 18 4 3.85 2.6 61.3 0.505 20 0.96 0.0178 19 5 4.95 2.6 60.8 0.491 21 0.87 0.0179 21 6 6.05 2.7 65.4 0.405 22 0.72 0.0146 20 7 7.15 3.5 68.5 0.346 29 0.65 0.0127 20 8 8.25 3.1 69.5 0.325 25 0.67 0.0123 18 9 9.35 3.1 70.4 0.307 26 0.67 0.0140 21 10 10.45 3.1 68.7 0.323 26 0.66 0.0139 21 220 Core core depth %hygro % Total density % LOI Xo SIRM SIRM/Xo sample [cm] moisture moisture [g/cm3] [E-6m3/kg] [Am2kg-1] [KAm-1] T7 2 1.65 3.4 61.7 0.594 17 1.11 0.0323 29 3 2.75 2.8 59.7 0.631 17 1.17 0.0318 27 4 3.85 2.5 57.9 0.689 15 1.26 0.0313 25 5 4.95 2.3 58.5 0.667 15 1.27 0.0290 23 6 6.05 2.9 62.8 0.570 18 1.16 0.0281 24 7 7.15 2.7 61.5 0.547 17 1.16 0.0263 23 8 8.25 2.5 61.3 0.574 16 1.18 0.0242 21 9 9.35 2.6 61.0 0.558 16 1.20 0.0268 22 10 10.45 2.7 61.8 0.560 17 1.16 0.0259 22 11 11.55 2.7 62.2 0.569 17 1.17 0.0243 21 12 12.65 2.7 62.7 0.598 17 1.18 0.0253 21 13 13.75 2.7 61.4 0.626 16 1.19 0.0316 26 14 14.85 2.6 61.6 0.617 17 1.21 0.0265 22 15 15.95 2.5 61.1 0.640 16 1.22 0.0266 22 16 17.05 2.3 59.9 0.592 16 0.58 0.0249 43 T8 T9 2 1.65 4.2 64.7 0.580 19 1.04 0.0270 26 3 2.75 3.7 64.5 0.567 19 1.09 0.0330 30 4 3.85 3.4 65.8 0.531 19 1.10 0.0297 27 5 4.95 3.2 64.4 0.581 17 1.16 0.0293 25 6 6.05 3.6 66.2 0.553 19 1.06 0.0271 26 7 7.15 3.7 67.5 0.492 20 0.96 0.0220 23 8 8.25 3.9 68.8 0.505 20 1.00 0.0237 24 9 9.35 3.6 67.1 0.523 20 1.01 0.0231 23 10 10.45 3.3 66.5 0.543 19 1.10 0.0273 25 11 11.55 3.2 66.4 0.556 18 1.12 0.0248 22 12 12.65 3.1 65.8 0.546 18 1.12 0.0267 24 13 13.75 3.1 64.9 0.557 18 1.11 0.0220 20 14 14.85 3.3 66.9 0.512 18 1.08 0.0240 22 2 1.65 3.6 63.4 0.169 21 0.98 0.0232 24 3 2.75 3.4 62.7 0.171 20 1.01 0.0251 25 4 3.85 3.8 63.7 0.164 20 0.99 0.0249 25 5 4.95 3.9 67.7 0.516 21 0.94 0.0239 25 6 6.05 3.9 69.6 0.447 24 0.81 0.0175 22 7 7.15 4.3 73.3 0.418 29 0.59 0.0138 23 8 8.25 4.0 71.4 0.426 27 0.75 0.0173 23 9 9.35 3.7 68.1 0.536 23 0.84 0.0168 20 10 10.45 3.3 65.1 0.581 21 0.93 0.0209 23 11 11.55 3.0 63.8 0.566 20 1.00 0.0222 22 12 12.65 3.1 63.9 0.529 20 1.00 0.0212 21 13 13.75 3.0 64.0 0.519 20 1.01 0.0179 18 14 14.85 3.0 64.4 0.555 20 1.01 0.0214 21 15 15.95 3.1 66.2 0.524 21 0.99 0.0168 17 16 17.05 3.2 67.2 0.489 21 0.98 0.0214 22 17 18.15 3.3 68.7 0.514 22 0.97 0.0182 19 18 19.25 3.8 70.1 0.442 25 0.98 0.0186 19 19 20.35 3.3 67.5 0.503 22 0.96 0.0177 18 20 21.45 3.0 63.6 0.577 19 1.00 0.0176 18 221 Core T10 core sample 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 depth [cm] I. 65 2.75 3.85 4.95 6.05 7.15 8.25 9.35 10.45 II. 55 12.65 13.75 14.85 15.95 17.05 18.15 19.25 20.35 21.45 22.55 %hygro moisture 3.4 3.0 3.4 3.2 4.2 4.0 3.7 3.6 3.4 4.0 3.6 3.8 3.8 3.9 3.8 4.4 4.6 5.0 3.7 3.3 % Total moisture 64.3 60.9 61.7 62.3 68.6 69.2 67.7 64.9 66.9 64.1 62.6 65.7 65.8 64.9 67.5 66.3 67.9 73.7 66.9 65.3 density [g/cm3] 0.520 0.648 0.611 0.642 0.514 0.483 0.522 0.573 0.497 0.555 0.615 0.596 0.581 0.584 0.539 0.521 0.533 0.426 0.532 0.599 % LOI 21 20 21 21 27 27 25 25 24 20 18 19 20 20 20 21 22 27 21 19 Xo [E-6m3/kg] 1.02 1.09 1.01 0.99 0.66 0.76 0.86 0.90 0.88 1.04 1.08 1.04 1.01 1.02 1.05 1.03 1.14 0.98 1.04 1.09 SIRM [Am2kg-1] 0.0324 0.0331 0.0305 0.0265 0.0145 0.0184 0.0232 0.0242 0.0209 0.0264 0.0255 0.0244 0.0232 0.0253 0.0260 0.0249 0.0256 0.0209 0.0253 0.0261 SIRM/Xo [KAm-1] 32 30 30 27 22 24 27 27 24 25 24 24 23 25 25 24 23 21 24 24 T11 2 1.65 3.1 67.1 0.484 20 1.03 0.0309 30 3 2.75 3.0 63.7 0.569 20 1.06 0.0306 29 4 3.85 2.8 62.5 0.599 19 1.10 0.0309 28 5 4.95 2.9 63.8 0.597 19 1.06 0.0282 27 6 6.05 2.8 66.0 0.494 21 0.98 0.0250 26 7 7.15 3.1 68.3 0.459 21 0.96 0.0235 25 8 8.25 3.0 68.1 0.471 23 0.97 0.0225 23 9 9.35 2.6 66.8 0.500 20 1.04 0.0246 24 10 10.45 2.4 65.8 0.532 19 1.08 0.0255 24 11 11.55 2.6 66.2 0.565 18 1.13 0.0260 23 12 12.65 2.6 65.5 0.524 18 1.11 0.0222 20 13 13.75 2.7 66.5 0.476 19 1.07 0.0238 22 14 14.85 2.8 66.0 0.524 19 1.06 0.0224 21 15 15.95 2.7 65.4 0.511 20 1.06 0.0233 22 16 17.05 2.5 66.4 0.537 19 1.08 0.0240 22 17 18.15 2.5 65.4 0.517 20 1.08 0.0235 22 18 19.25 2.5 65.7 0.549 19 1.10 0.0235 21 19 20.35 2.5 67.1 0.562 20 1.10 0.0229 21 20 21.45 2.3 66.7 0.535 18 1.10 0.0236 22 222 Core core depth %hygro % Total density % LOI sample [cm] moisture moisture [g/cm3] K1 2 3 4 5 6 7 8 9 10 1.65 2.75 3.85 4.95 6.05 7.15 8.25 9.35 10.45 6.0 6.0 5.7 5.5 5.5 5.5 5.6 5.5 5.8 79.7 78.9 79.3 79.3 79.2 79.7 79.3 79.9 81.0 0.325 0.332 0.328 0.336 0.318 0.303 0.301 0.295 0.289 40 39 37 35 36 36 36 36 38 Xo [E-6m3/kg] 0.37 0.29 0.27 0.26 0.25 0.23 0.24 0.22 0.21 SIRM [Am2kg-1] 7.12E-03 5.40E-03 4.37E-03 4.06E-03 3.97E-03 3.64E-03 3.76E-03 3.27E-03 3.33E-03 SIRM/Xo [KAm-1] 19 19 16 16 16 16 16 15 16 K2 K4 2 1.65 5.7 78.0 0.334 36 0.51 1.19E-02 23 3 2.75 6.2 78.5 0.303 39 0.45 9.97E-03 22 4 3.85 5.9 79.2 0.327 37 0.35 7.59E-03 22 5 4.95 6.1 80.7 0.286 38 0.27 5.82E-03 21 6 6.05 5.7 80.7 0.292 37 0.23 4.57E-03 20 7 7.15 5.7 80.6 0.283 37 0.23 4.73E-03 21 8 8.25 5.7 81.2 0.263 38 0.23 4.48E-03 20 9 9.35 6.1 81.1 0.233 39 0.23 4.12E-03 18 10 10.45 5.9 81.5 0.288 37 0.20 4.02E-03 20 11 11.55 6.2 82.0 0.263 40 0.20 3.75E-03 19 12 12.65 6.0 82.2 0.265 39 0.18 3.06E-03 17 13 13.75 5.6 81.6 0.286 36 0.18 3.22E-03 18 14 14.85 5.8 83.0 0.254 38 0.18 2.93E-03 16 15 15.95 5.7 81.2 0.284 38 0.18 2.85E-03 16 16 17.05 5.5 81.1 0.277 35 0.18 3.34E-03 18 17 18.15 5.2 80.2 0.300 36 0.19 3.28E-03 18 18 19.25 5.1 80.2 0.289 36 0.17 2.97E-03 17 19 20.35 5.0 79.4 0.317 34 0.16 2.37E-03 15 20 21.45 5.2 79.7 0.314 34 0.16 2.34E-03 14 21 22.55 4.9 79.0 0.310 34 0.17 2.74E-03 17 22 23.65 5.1 80.6 0.291 37 0.16 2.29E-03 15 2 1.65 2.0 56.9 0.646 18 0.74 1.53E-02 21 3 2.75 1.7 54.3 0.681 16 0.66 1.33E-02 20 4 3.85 1.8 61.4 0.541 19 0.60 1.20E-02 20 5 4.95 2.4 69.9 0.420 24 0.59 1.00E-02 17 6 6.05 1.9 63.0 0.475 19 0.47 9.08E-03 19 7 7.15 2.3 69.5 0.379 22 0.40 7.68E-03 19 8 8.25 2.6 74.7 0.291 28 0.39 7.22E-03 18 223 Core C1 core sample 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 depth [cm] 0.55 I. 65 2.75 3.85 4.95 6.05 7.15 8.25 9.35 10.45 II. 55 12.65 13.75 14.85 15.95 17.05 18.15 19.25 20.35 %hygro moisture 4.6 3.8 4.0 3.7 3.6 3.5 3.7 3.7 3.9 3.7 3.6 3.6 3.5 3.5 3.6 3.6 2.5 1.6 3.3 % Total moisture 81.1 71.0 72.5 71.4 71.7 72.2 73.8 74.4 73.6 73.0 72.6 73.0 72.1 72.1 72.5 73.1 67.0 60.7 75.4 density [g/cm3] 0.232 0.433 0.446 0.436 0.414 0.387 0.373 0.364 0.387 0.390 0.392 0.414 0.401 0.415 0.406 0.407 0.455 0.525 0.342 % LOI 27 26 25 24 24 24 26 26 25 24 24 24 24 25 25 26 19 13 25 Xo [E-6m3/kg] 0.77 0.87 0.97 1.03 1.14 1.16 1.00 0.87 0.85 0.84 0.84 0.78 0.73 0.73 0.71 0.67 1.14 1.34 0.88 SIRM [Am2kg-1] 0.0187 0.0204 0.0211 0.0210 0.0191 0.0203 0.0187 0.0173 0.0156 0.0165 0.0172 0.0154 0.0136 0.0129 0.0124 0.0106 0.0129 0.0138 0.0156 SIRM/Xo [KAm-1] 24 23 22 20 17 18 19 20 18 20 21 20 19 18 17 16 11 10 18 C2 C3 2 1.65 3.9 69.7 0.437 26 0.88 0.0205 23 3 2.75 3.9 67.3 0.502 24 0.97 0.0210 22 4 3.85 3.9 67.8 0.468 24 0.91 0.0210 23 5 4.95 4.0 69.8 0.443 25 0.92 0.0203 22 6 6.05 3.9 70.2 0.435 25 0.91 0.0198 22 7 7.15 3.8 72.3 0.437 25 0.91 0.0187 20 8 8.25 4.0 73.4 0.400 26 0.86 0.0181 21 9 9.35 4.1 73.8 0.371 26 0.81 0.0166 20 10 10.45 3.8 73.1 0.396 25 0.87 0.0163 19 11 11.55 3.7 71.8 0.400 24 0.81 0.0171 21 12 12.65 3.6 70.2 0.432 24 0.82 0.0179 22 13 13.75 3.7 70.0 0.467 24 0.79 0.0151 19 14 14.85 3.4 69.3 0.445 25 0.76 0.0151 20 15 15.95 3.3 70.0 0.462 24 0.69 0.0130 19 16 17.05 3.2 70.0 0.443 24 0.69 0.0128 18 17 18.15 3.2 71.4 0.415 25 0.69 0.0123 18 2 1.65 4.1 74.7 0.353 26 0.83 0.0195 23 3 2.75 3.8 68.2 0.468 24 0.90 0.0197 22 4 3.85 3.6 69.4 0.437 25 0.88 0.0203 23 5 4.95 3.5 69.7 0.473 25 0.93 0.0203 22 6 6.05 3.5 70.4 0.445 25 0.90 0.0196 22 7 7.15 3.7 71.4 0.426 26 0.88 0.0188 21 8 8.25 4.0 73.3 0.431 26 0.83 0.0185 22 9 9.35 4.0 72.8 0.406 26 0.80 0.0180 23 10 10.45 3.9 71.1 0.423 25 0.81 0.0177 22 11 11.55 3.7 70.3 0.416 24 0.82 0.0181 22 12 12.65 3.9 70.6 0.411 25 0.81 0.0177 22 13 13.75 3.7 71.0 0.454 25 0.79 0.0170 22 14 14.85 3.8 71.5 0.450 24 0.76 0.0159 21 15 15.95 3.9 70.2 0.445 24 0.74 0.0151 20 16 17.05 3.6 70.1 0.439 24 0.73 0.0141 19 17 18.15 3.4 67.5 0.479 22 0.79 0.0138 17 18 19.25 3.9 72.6 0.366 26 0.77 0.0157 20 Appendix D Autochthonous Sediment Data, Sediment Geochemistry and Particle Size Data Carbonate fraction (%) Biogenic Silica fraction (%) Geochemistry : Macro-Elements (mg kg"1) Geochemistry : Heavy Metals (mg kg"1) Particle Size Data Carbonate data 225 core M5 %C03 core M8 %C03 core M12 %C03 sample sample sample 3 3.5 2 1.5 2 4.2 5 3.3 4 3.0 4 4.3 7 3.5 6 2.3 6 4.6 9 2.8 8 3.6 8 2.2 11 2.9 10 3.6 10 3.0 15 3.1 12 4.5 13 2.6 17 3.7 14 4.5 15 2.4 18 3.1 16 3.3 17 2.9 21 2.9 18 3.4 19 2.9 23 2.9 20 3.7 21 3.3 22 3.8 24 2.8 24 3.4 core T4 % C03 core T8 % C03 sample # sample # corrected 2 3.7 2 4.8 3 3.7 3 4.4 4 4.1 4 4.2 5 3.4 5 4.5 6 3.4 6 4.5 7 3.5 7 4.5 8 3.3 8 4.3 9 3.4 9 4.3 10 3.6 10 4.2 11 4.3 12 4.2 13 4.2 14 4.5 Core C2 sample # 2 4 6 8 10 14 16 % C03 6.9 7.4 7.2 8.4 7.6 7.1 7.0 core K1 sample # 2 3 4 5 6 7 8 9 10 % C03 10.1 9.7 8.8 9.3 9.5 9.4 9.1 9.0 9.5 Biogenic silica data 226 M18 M12 sample id %bio si sample id %bio si 2 8.5 2 11.9 4 7.8 4 9.7 6 6.9 6 10.1 8 7.3 8 7.8 10 6.9 10 8.1 12 5.3 12 7.7 14 4.5 14 9.8 16 6.2 16 9.4 18 5.4 18 9.1 20 5.5 20 11.2 22 6.8 22 10.1 24 10.1 T9 K2 C3 sample id %bio si sample id %bio si sample id %bio si 2 7.9 2 11.8 3 9.8 4 10.4 6 13.8 5 9.1 6 10.0 8 14.7 7 11.0 8 11.2 12 15.3 9 10.6 10 9.7 14 13.4 11 10.0 12 8.4 16 14.0 13 9.0 14 9.7 18 13.8 15 9.2 16 9.6 20 13.3 17 7.7 22 8.3 227 CD . _eoo>o>CMmo>mcoioo>eo £ o>co c o r O T i - T j - c O ' l - T t T i - T j - o CM ^  f~ T - OI T - CM •>- CM CM •>-T * T * CD T}- O CM CO in m CM 1 m <V co cu c u. £ o CM in Oi in m m Oi r- oi CM o> If) o co CO m , — CM o> o> 00 CO CO r» 00 •Ti- r- a> CO r- a> oo 05 cr> O T— m O) Tif CD T™ o r- CO o T— m oo o> oi co r- CO o o r- CD OJ ol O) o ^ — r- to T — l CM CM co co CM CM CM CM CM CM CM co co CM CM CM oo P D)CM CM ^ <° <° •5 E ^ — m T — CM co ^ — r- co m Ol CM o 1 — CO T ~ CO m co CO OJ CO co , — in oo CO in r- CD m o> CM CO CD 00 o O CO CO CM m co co ^ — T— o> O co 1 to r- co r- co CD co m r- r- co CD CO co • cn co cz o S CM CM in in m CM oo O) Oi CM o> m o co T — co m CM r-T — TJ— oi 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N o t c o i n i O T - n o T -— T - m c o T t T t c N c o m o o o o Cn CN CMCNCOCOCOCOCOCNCO m co Tt co o> C M o CO T - CO C M C O C M m m m m m co O) o CM CN Tt CO od m in m m m m r~ 00 CO m co "t CD CM X— X— x— CM CN m m m in m m at O) O) CO 00 00 Tt Tt Tt Tt Tt Tt o o E CD SZ o o CD O cn > cn > co cn > ra -a c co cn % > ft h* co co co m co m Tt in T - • . co co co j£ o «o c co € ™ CO > CO CO CD co -Q 5 cn > co co Tt o CO n. co CM co m CO oo T— T- X— T- CM in m m CM CM CM CM CM CM CM CM CM CM CN CM CM i— T— x— Tj— x— T^  E E 5 E E E E E E E E E 8 c *. CD ° £ m -o CO X3 Tt Q . ?1 -*rf t 3 T— T— I I I CM CM CM O E E E S i 2 8 8 «= C CD CD •a "6 o> CO o o in i : CN 230 o CN CN .O. lO m o CO w 3 "5 E > 03 CU I CM CO CO o O CO co CN co r- r- co T- o T- o> oo O) o> CM o o> aii XL 1 CM 1 CO i CO 1 d CM CO • cb cd CM 1 1 CM • o 1 o co i co' 1 CO 1 d • o" • oi CM D) E, CO co r- CO CM a> r- 00 o r-. 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TJ "6 o o d • CM 231 CD m CM I 5 O) E CM CO o 0 0 CM CM o m 0 > m T— co r » co CO i n m m T -OJ co m CO CO CD 0 0 o CM CO CO co CO CO CO o o o co • CD r - co r - CO co r - CM OJ r - r - r - r - r -cn ^ oo i n CM o o> co oo m i n O co —^ CM o> CM T— CM 0 0 co 0 0 i n CO CD •«r o> r- r- CM o CM oo co CO oo o> T - o m CM 0 0 co co r- r- CM o co CM CO r- CO CO y— CD 0 0 0 0 co CD o> r- co m CD co CM co co CD CM Tt •»* •«*• **• •*r T— T— CM o CM CO CO CO c CD E CD o CQ CD h-S> o o M— o "So E CD SZ o o CD O OJ „ CQ §» S 3 o CO O) 5 £ CD -=S —- CO i n =* CM CO CO XL co CO E C L CD T J _CD C L E to 73. CO oo CO o> o> CO 1- o CM m 1- cn O) m —^ co CM m cn co •«r m r- i n o CO CO m o i n r - o co r - o CM o CM T— 0 0 o o CM cn cn CD CM CM T— r— cn oo cn 1 m CM m co r-~ y— T — CO m CD cn CM co o cn CO o CM co o <o r- m co CM o> m oo r - OI CM cn o O -<r cn CD cn 0 0 i— cn o> m co 0 0 0 0 CD m CD r~ CD co 0 0 CO co r - CO CO i f —^ r - CM CO CO cn co CM CM • f m •*»• m m m m m m co i— CM m CD m m m m —^ oo CM O cn ,— CO 0 0 m cn CO CM CM 0 0 o cn 0 0 CD m m cn o m • f O O CD CM CM • t m CO cn CM CO 0 0 CM m CO CM •»)• r -y— r » CO m r- o CO cn •+ CM cn m co CO CD CM cn CD CM cn CM 0 0 CM CO co 1— CM o 0 0 cn CM CM CM CM CO CM ,— CM CO CM CO CO CO CO CO CO *— CO CO CO CO co co i n co cn O O y— CM r- y— T— oo —^ co oo CO CO CM m m CM cn m CM CO i n CD o o cn oo CD CM CO r - m m o m m CO 0 0 T— r- CD r-~ y— o o CM r - r - CN ' o T— CM TT •<cr m m i n m —^ T- m m m CO r- o> CD o> co co r- r- CM o cn co cn oo T ~ oo r - co co CM m m CM T— O) co co co co m m m CO ' CM CM o CM C O C O C O C O lO CO CM CM CM co C O co cn CO CO oo cn co i n CM i n oo m oo CO 1— CO m m CO o o o C O 0 0 oo oo co oo T— CO cn T— r- cn oo T— T— ,— T— —^ y— 1 co co CM CM CM CM co CM co i n m CM CM CM co co co r- m m m m m m m m m m m m CO oo o CM CD co o co CM co y—" co CO od o CM T * o oo' o T— T - CM CM CM TJ-CO > CO CO 0 0 o CM CO ch 2 2 ch ch I* co co TJ C CD T— CM CO T J T J T J to to 1o i i i cn cn cn % co c co -S> .8 > CO T J ez CO > JZl . 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E CO -n Tt cq co co -r- Tt co cn d d d d iri d o> d C O G ) G ) O ) O > O ) N C 0 C O » C O O > C N O > T t r - - C N C N d CM d •«*• T T CM d d d TtinTj-mminTrmm OOTtCOCOCOOOCOCOT— d d d d d d d d - ^ -i n m i n m m i n m m i n co oo o CN * cq oq o CO r r i t o ' d o ' c i x f s d T - T - T - T - CM Tt OTI t f d d CN T- CM co r - cn o d d CO T - CM m x- Tt o d d cn > co 3»« CM tt O CN Tt CD cn CO 00 T - T - T - T - r-c n c n c n c n c n c n c n c n c n g^ www T — CN co T3 T3 T3 cn cn cn oo co co o in to d d d d cn cn cn o t t Tt tt Tt CM m m m CN f-~ CN ' d CO OJ 00 O CM d d d d o m CM to co > co •o c CO 1 co c co s 5° .cj co xa cn £ > 5 „ CD 8 m CD O CD CN co p in co d d d t t d co co co 1 O ) Tf CM N CO CM d d CM d m m m T - ' d d m co d CM co CD O) CD cn > co cn CD > x : co y oo oo oo ^ 1^ T - i - T -5 2 2 2 5 , 5 o co cn cn J , cn > co co Q. 1 8 C 2> CD w C . 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E CD O _CD CL E CO TI r - c o m c D O O C D C M c o i o c M C M i o c O T t i - r - T t T - T - T - C O I O I O I O C O T -co in CO CD CM . oi * i>. m f» C M C M C M C O T - 0 » T t r - 0 > ^ —' CO CO T- T~ T- m CM T t C O T - C O C O O r - C O O T t M O t O ' - i D O c o T - i n COTtTt lO lOtOCOCOlO in in in in in r— oo CD T— co CM CO Tt CD in in in m m CD co iri oo —^ ^ — T— ra > co • C O o 2 co T _ CO IO r-p CD T— T— CO to CO CO CO c o o o o ra > co N O 0 1 n m ( M f l 0 O n 2 £ £ C N " ^ S ^ C O co CD O T t T t T t m co co co «7 ra > co TJ C co o CL m CD c co 2 > £ co TJ C CO CO CO •2 CD •Q 2S CO CD co xi m io to ra > CO CO CD o CL CO _ > 5= co xi « "5 in m m CDT-T-T-• I • *P I • • vP C O C O C O c > ~ C O C O C O c > c i o c j i O T j c i o o i o J - i CO 8 8 CD g CD o> =6 "6 CO S N CM N S iri CM T t T t T t CO CO to T t co CM r- i CM T t " r -CD r-~ o o o o o o d d d CM CO T-TJ TJ TJ 00 CO CO "3 13 « SI 'S " E E © co co o TJ O C c e o CO CO to To co o o ~ ttito z z w = •= 5 co co ^ V) CO to T- CM CO ^ Ji, ^ www 234 oo ^ C O O ) N ^ co iri o 0 0 C D C O x— C O C O o> 1— m 0 0 C M X—: C D d d C N C D C N X— C N X— o o O o O T— O o o o X— T— x— X— T— x— _ TJ- r - 0 0 „ T £ O S CN d «» **• m ° o T - T - m v «. r - Tt g d d ~ co oo C O -^s O CD) C N ^ < N O ) Tt oo r - "* COi |s» d 9 co T - CM p • r ^ ' » 7 C ? C ? » - T - ' - T - ^ d d N O f CN C O T— C O T— CD) co ^ C N cn 4 E co co Tt o T™ oo co CO h- T— cq C O co Tt CO C O oq ** ro 1-d d d C O d d d xr- XT- 5 " d T T d d CN d d r-" d co ** Tt Tt Tt m Tt Tt Tt • ** i x— CN co CO cu E > CO cu X d O £ o o o cr to E cu sz o o cu O r- ^ •tj- cn C M ^ «? at 5 3 C N O ) 6 -§ 0 0 -^s co cn C M ^ C N O ) •6 E sz ^ "S. E cu o •o w 0 ) a. E co 2 Tt co m C M oq CD Ol Tt (35 CO C O m d Tt d d d C M d d r-" d d o o o C M CN o x— m co CO oo o> a> Tt co i— x— C D d h-° Tt Tt" Tt Tt d C M d Tt Tt CO CO CD CO CO co CO CO CO CO co CO Tt m m Tt C M C M r-- co in d d d d d d d d d d d d co C D T— 0 0 Tt ffl'r 6 ro CN CM CO m m m m m r- 0 0 CD T— C O CN d Tt d m m m in co T—' d d d x— x— cn > C O "3 Tt co m r - o> C O C O o co o co o co o co o C O o CO > co C M in d d m h- T -to co co Tt <q d 9 O * ^ (fl N O n d o d did o cn > co TJ c CO o a. co -a i ? £ i « J O « • * £ m m m cu co co co or* itz O O O m T3 m m m co > CO O) <j) CO -•—' c? b co cu € o lO cu c co 2 > £ ™ CO T3 Co CO ^ M CU c= xi XJ X; 8 8 £ aj CU .OJ 73 "5 T - ; CO Tt o d d C M C M T -O CO C O d C M d T - C O C O CM CM CO •r^ d o" o o o O C D O o d d CN CO TJ 73 to to •a to ( J UJ W co 8 •a c c Cl) c0 cO cO o o "S CO T3 c co _ to to (/) O O = ^ 0 2 cn Z Z W c c » co co i: co oo oo T - C M co i i i W W W Particle size data Core sample id depth (cm) C3 2 1.65 4 3.85 6 6.05 8 8.25 10 10.45 12 12.65 14 14.85 16 17.05 18 19.25 % sand % coai >63 silt 10.5 5.5 8.6 3.9 6.3 3.2 6.8 3.2 6.6 3.3 5.4 3.1 6.1 1.9 9.0 5.0 13.0 5.0 % medium % fine silt silt 17.9 55.1 13.8 63.9 15.1 64.4 13.4 64.0 15.3 64.6 13.9 65.9 13.4 67.1 14.6 60.6 12.9 58.0 % very fine % clay silt 4.1 7.8 2.8 7.1 3.8 7.6 4.8 8.0 3.1 7.1 4.2 7.9 3.7 7.8 3.5 7.3 6.7 5.6 M12 3 2.75 5 4.95 7 7.15 9 9.35 11 11.55 13 13.75 15 15.95 17 18.15 M18 3 2.75 5 4.95 7 7.15 9 9.35 11 11.55 13 13.75 15 15.95 17 18.15 19 20.35 21 22.55 T9 3 2.75 5 4.95 7 7.15 9 9.35 11 11.55 13 13.75 15 15.95 17 18.15 18b 19.25 20 21.45 3.8 4.9 5.4 4.4 4.3 4.2 5.8 5.1 21.1 9.4 13.2 12.5 13.6 10.0 15.7 8.9 15.9 11.9 17.7 14.8 20.2 14.7 16.2 10.0 28.1 8.6 17.4 11.4 4.7 4.3 5.6 3.1 10.1 2.0 8.4 3.3 5.3 3.9 6.9 0.7 5.4 3.4 5.1 1.1 4.8 1.2 4.7 4.2 12.2 62.9 10.3 52.2 10.5 55.2 10.7 51.5 11.7 55.2 17.8 37 15.2 67.3 15.8 45.2 17.2 34.4 18.9 15.7 18.4 24.9 16.4 32.4 20.3 18.7 24.6 16.8 21.1 17.2 21.3 28.8 18.1 25.9 22.2 30.4 15.9 63.5 19.0 63.8 12.0 62.8 16.3 62.4 13.0 69.8 14.8 69.0 14.5 67.8 12.3 71.7 9.5 73.6 11.7 66.0 11.9 9.2 25.4 7.3 19.6 9.2 20.8 13 20 8.8 14.9 24.7 6.7 8.2 14.7 18.3 5.7 12.4 10.2 29.6 10.1 23.8 9.1 18.2 9.1 26.8 7.7 19.4 10.6 16.7 7.4 16.5 5.2 14.3 5.1 15.0 5.0 6.6 3.3 6.0 3.4 9.4 3.0 6.6 3.0 5.2 3.4 5.1 3.2 6.2 3.0 6.5 3.3 7.6 6.1 7.4 -Each fraction is expressed as a % of the total weight of an initial sample. -The sand fraction of M12 is not presented as the samples were contaminated. Each fraction for M12 is expressed as a % of the total weight of less than 63 micron particles 236 Appendix E 1 3 7Cs and 2 1 0Pb Data of Master Cores 137Cs data [Bq kg1] 210Pb data [ Bq g1] Note: Errors associated with the 137Cs measurements were calculated by summation of 5% error in the efficiency calibration and 2o in statistical counting of each sample's peak area. 237 Cs activity data Core M5 Core M16 Sample depth Cs activity Error Sample depth Cs activity Error Id [cm] [Bq/Kg] [Bq/Kg] Id [cm] [Bq/Kg] [Bq/Kg] 2 1.65 61 8 2 1.65 80 8 3 2.75 3 2.75 4 3.85 62 29 4 3.85 5 4.95 80 22 5 4.95 117 17 6 6.05 6 6.05 122 9 7 7.15 132 27 7 7.15 159 16 8 8.25 92 15 8 8.25 189 10 9 9.35 113 12 9 9.35 193 15 10 10.45 142 30 10 10.45 181 13 11 11.55 177 25 11 11.55 185 18 12 12.65 228 18 12 12.65 112 12 13 13.75 191 45 13 13.75 134 10 14 14.85 251 10 14 14.85 63 6 15 15.95 209 29 15 15.95 37 11 16 17.05 111 20 16 17.05 51 17 17 18.15 90 20 17 18.15 21 6 18 19.25 135 35 18 19.25 23 12 19 20.35 116 22 19 20.35 20 21.45 61 6 20 21.45 21 5 21 22.55 21 22.55 22 23.65 38 13 22 23.65 15 less than 23 24.75 36 12 23 24.75 24 25.85 14 less than Core C1 Core M11 Sample depth Cs activity Error Sample depth Cs activity Error Id [cm] [Bq/Kg] [Bq/Kg] Id [cm] [Bq/Kg] [Bq/Kg] 2 1.65 113 12 2 1.65 3 2.75 3 2.75 4 3.85 134 13 4 3.85 35 9 5 4.95 5 4.95 6 6.05 184 20 6 6.05 7 7.15 224 21 7 7.15 8 8.25 263 28 8 8.25 9 9.35 255 30 9 9.35 10 10.45 213 31 10 10.45 11 11.55 150 26 11 11.55 157 15 12 12.65 78 10 12 12.65 217 22 13 13.75 43 10 13 13.75 238 10 14 14.85 35 less than 14 14.85 275 20 15 15.95 15 15.95 224 13 16 17.05 131 14 16 17.05 114 11 17 18.15 17 18.15 18 19.25 18 19.25 107 11 19 20.35 30 less than 19 20.35 49 8 238 CoreK2 Sample depth Cs activity Error Id [cm] [Bq/Kg] [Bq/Kg] 2 1.65 120 14 3 2.75 4 3.85 153 16 5 4.95 6 6.05 178 25 1 7.15 189 13 8 8.25 217 23 9 9.35 176 18 10 10.45 158 35 11 11.55 84 18 12 12.65 42 8 13 13.75 14 14.85 33 less than 15 15.95 16 17.05 36 less than 17 18.15 18 19.25 19 20.35 20 21.45 22 less than Core T10 Sample depth Cs activity Error Id [cm] [Bq/Kg] [Bq/Kg] 2 1.65 228 22 3 2.75 245 25 4 3.85 103 21 5 4.95 29 13 6 6.05 7 7.15 8 8.25 9 9.35 10 10.45 12 less than 11 11.55 12 12.65 13 13.75 14 14.85 15 15.95 15 less than 16 17.05 17 18.15 18 19.25 19 20.35 20 21.45 24 less than "less than" means measurements were below minimum detectable activity Ld-210 activity Sample depth interval Pb-210 Precision Id top (cm) bottom (cm) (Bq/g) 1 std (Bq/g) CoreM5 2 1.1 2.2 0.254 6.4 4 3.3 4.4 0.221 8.8 6 5.5 6.6 0.146 5.0 8 7.7 8.8 0.103 5.9 10 9.9 11.0 0.135 5.5 12 12.1 13.2 0.045 9.0 14 14.3 15.4 0.113 5.0 16 16.5 17.6 0.058 8.4 18 18.7 19.8 0.047 4.4 20 20.9 22.0 0.118 4.4 22 23.1 24.2 0.065 4.1 2 1.1 2.2 0.220 8.3 4 3.3 4.4 0.243 8.6 6 5.5 6.6 0.142 5.3 8 7.7 8.8 0.131 5.2 10 9.9 11.0 0.103 5.8 12 12.1 13.2 0.067 5.4 14 14.3 15.4 0.115 2.5 16 16.5 17.6 0.066 5.4 18 18.7 19.8 0.130 2.4 20 20.9 22.0 0.099 4.8 22 23.1 24.2 0.066 5.3 24 25.3 26.4 0.048 5.6 Core M11 1 0.0 1.1 0.292 6.6 3 2.2 3.3 0.112 11.6 5 4.4 5.5 0.294 6.5 7 6.6 7.7 0.294 3.9 9 8.8 9.9 0.143 6.3 11 11.0 12.1 0.197 4.0 13 13.2 14.3 0.084 3.8 15 15.4 16.5 0.107 3.5 17 17.6 18.7 0.178 2.9 19 19.8 20.9 0.079 5.7 21 22.0 23.1 0.119 6.3 23 24.2 25.3 0.109 6.3 25 26.4 27.5 0.134 5.9 Core T2 2 1.1 2.2 0.174 5.6 4 3.3 4.4 0.166 7.7 6 5.5 6.6 0.095 7.2 8 7.7 8.8 0.129 4.2 10 9.9 11.0 0.103 6.5 12 12.1 13.2 0.071 5.3 14 14.3 15.4 0.076 6.1 16 16.5 17.6 0.520 6.2 -linear interpolation was used to determine Pb-210 activity at 1.1 cm interval Sample depth interval Pb-210 Precision Core T10 Id top (cm) bottom (cm) (Bq/g) 1 std (B( 2 1.1 2.2 0.241 6.9 4 3.3 4.4 0.133 8.5 6 5.5 6.6 0.061 8.6 8 7.7 8.8 0.082 5.6 10 9.9 11.0 0.043 5.8 12 12.1 13.2 0.031 5.6 14 14.3 15.4 0.021 9.8 16 16.5 17.6 0.011 15.8 18 18.7 19.8 0.010 12.0 20 20.9 22.0 0.010 10.2 2 1.1 2.2 0.264 6.8 4 3.3 4.4 0.202 4.9 6 5.5 6.6 0.290 4.5 8 7.7 8.8 0.161 3.8 10 9.9 11.0 0.045 7.1 12 12.1 13.2 0.038 6.5 14 14.3 15.4 0.068 4.5 16 16.5 17.6 0.052 6.5 18 18.7 19.8 0.046 6.1 3 2.2 3.3 0.256 6.9 5 4.4 5.5 0.230 6.5 7 6.6 7.7 0.200 3.8 9 8.8 9.9 0.147 3.8 11 11.0 12.1 0.126 4.0 13 13.2 14.3 0.098 4.5 15 15.4 16.5 0.051 4.9 17 17.6 18.7 0.091 4.7 19 19.8 20.9 0.045 6.5 21 22.0 23.1 0.032 6.5 -linear interpolation was used to determine Pb-210 activity at 1.1 cm interval Appendix F Trap Efficiency Data 241 Volume (m3) Total Mean Flow Q (mV) C/I ratio Trap Efficiency (%) Maggie Lake 6.25 x 107 5.1 x 107- 2.6 x 108 1.23-0.24 88-95 Toquart Lake 2.24 x 107 5.9 x 107-3.0x 108 0.38- 0.08 75-91 Kite Lake 3.66 x 106 2.51xl07-1.3xl08 0.15- 0.03 56- 84 Clayoquot Lake 9.28 x 106 5.86 x 107- 2.9 x 108 0.16- 0.03 56- 84 Notes: -Volume was determined by digital planimetry of the bathymetric maps. -Total Mean Flow range is determined as outlined in section 3.5. Maximum and Minimum values are based on the confidence range of the unit hydrological estimate lq (Church, 1997). -C/I ratio is the lake capacity to annual water inflow (Brune, 1953). -Trap efficiency is calculated from Brune's (1953) fine sediment (lower) curve, for which an equation was derived by Gill (1979). -Volume of Clayoquot Lake includes both the upper and lower basin. 242 Appendix G Catchment Sediment Yield Data The following appendix includes: -Catchment sediment yield data for sedimentary zones in each lake showing mass accumulation for each zone in each core, followed by the lake-wide calculation of sediment yield. -Data used to demonstrate the bias of using only three cores in calculating whole-lake sediment yield estimates. -Calculations of yield for Kite Lake at boundaries that coincide with zonal boundaries in other lakes. Notes: -MSA refers to mass sediment accumulation, while MSAR refers to the mass sediment accumulation rate -Sediment depositional area is defined by the 10 m contour and the 20 m contour (see text for discussion in section 3.5). -Area refers to the area of the Thiessen polygon defined for each core, which has either a 10 or 20 m contour outer boundary. -Density, and LOI are average values over the specific depth interval, while carbonate and biogenic silica are average values over the zones. 243 Maggie Lake ZONE M-A Core depth zone length Area (cm2) Area (cm2) density LOI MSA-10 MSA-20 interval (cm) (cm) 10m bdy 20 m bdy (g7cm3) (%) (t) (t) M2 14.3-20.9 6.6 1.07E+09 8.94E+08 0.725 10 4.6E+03 3.9E+03 M3 13.2-20.9 7.7 1.31E+09 6.98E+08 0.742 12 6.6E+03 3.5E+03 M4 16.5-20.9 4.4 1.07E+09 8.89E+08 0.656 16 2.6E+03 2.2E+03 M5 19.8-22 2.2 1.16E+09 1.09E+09 0.631 13 1.4E+03 1.3E+03 M18 16.5-20.9 4.4 1.94E+09 1.46E+09 0.544 14 4.0E+03 3.0E+03 M1 n/a M17 n/a M16 14.3-17.6 3.3 2.20E+09 2.00E+09 0.595 18 3.6E+03 3.2E+03 M15 11-15.4 4.4 1.95E+09 1.85E+09 0.641 16 4.6E+03 4.4E+03 M14 n/a M13 8-10.2 2.2 2.20E+09 1.64E+09 0.591 16 2.4E+03 1.8E+03 M12 14.3-20.9 6.6 1.63E+09 1.46E+09 0.481 18 4.2E+03 3.8E+03 M11 16.5-20.9 4.4 1.78E+09 1.60E+09 0.499 17 3.2E+03 2.9E+03 M9 n/a M8 14.3-17.6 3.3 1.19E+09 1.05E+09 0.563 16 1.9E+03 1.6E+03 M7 7.2-12.2 5 1.94E+09 1.39E+09 0.808 13 6.9E+03 4.9E+03 AVG 0.623 15 3.8E+03 STDS 0.099 3 1.7E+03 ZONE M-B Core depth zone length Area (cm2) Area (cm2) density LOI MSA-10 MSA-20 interval (cm) (cm) 10m bdy 20 m bdy (g/cm3) (%) (t) (t) M2 9.9-14.3 4.4 1.07E+09 8.94E+08 0.793 9 3.4E+03 2.8E+03 M3 11-14.3 3.3 1.31E+09 6.98E+08 0.923 8 3.7E+03 2.0E+03 M4 13.2-16.5 3.3 1.07E+09 8.89E+08 0.785 11 2.5E+03 2.0E+03 M5 13.2-19.8 6.6 1.16E+09 1.09E+09 0.783 9 5.4E+03 5.1E+03 M18 11-16.5 5.5 1.94E+09 1.46E+09 0.816 8 8.0E+03 6.0E+03 M1 N/A M17 N/A M16 11-14.3 3.3 2.20E+09 2.00E+09 0.850 11 5.5E+03 5.0E+03 M15 8.8-11 2.2 1.45E+09 1.37E+09 0.832 11 2.4E+03 2.2E+03 M14 8.8-11 2.2 1.07E+09 9.54E+08 0.693 12 1.4E+03 1.3E+03 M13 5.8-8 2.2 1.45E+09 1.03E+09 0.673 14 1.8E+03 1.3E+03 M12 12.1-14.3 2.2 1.01E+09 9.70E+08 0.754 12 1.5E+03 1.4E+03 M11 11-16.5 5.5 1.32E+09 1.19E+09 0.647 13 4.1E+03 3.7E+03 M9 12.1-15.4 3.3 1.71E+09 1.48E+09 0.756 12 3.8E+03 3.2E+03 M8 11-15.4 4.4 1.04E+09 8.95E+08 0.723 12 2.9E+03 2.5E+03 M7 5-7.2 2.2 1.94E+09 1.39E+09 0.891 12 3.4E+03 2.4E+03 AVG 0.780 11 3.5E+03 STDS 0.080 2 1.8E+03 244 ZONE M-C Core depth zone length Area (cm2) Area (cm2) density LOI MSA-10 MSA-20 interval (cm) (cm) 10m bdy 20 m bdy (g/cm3) (%) (t) (t) M2 5.5-9.9 4.4 1.07E+09 8.94E+08 0.785 11 3.3E+03 2.7E+03 M3 5.5-11 5.5 1.31E+09 6.98E+08 0.822 9 5.4E+03 2.9E+03 M4 4.4-13.2 8.8 1.03E+09 8.53E+08 0.819 10 6.6E+03 5.5E+03 M5 6.6-13.2 6.6 7.77E+08 7.77E+08 0.700 11 3.2E+03 3.2E+03 M18 4.4-11 6.6 1.33E+09 8.79E+08 0.846 11 6.6E+03 4.4E+03 M1 3.3-7.7 4.4 8.65E+08 7.69E+08 0.767 13 2.5E+03 2.3E+03 M17 4.4-16.5 12.1 1.12E+09 1.06E+09 0.793 12 9.5E+03 9.0E+03 M16 5.5-11 5.5 1.04E+09 9.04E+08 0.804 13 4.0E+03 3.5E+03 M15 4.4-8.8 4.4 1.45E+09 1.37E+09 0.754 13 4.2E+03 4.0E+03 M14 4.4-8.8 4.4 9.75E+08 8.69E+08 0.688 14 2.5E+03 2.3E+03 M13 1.4-5.8 4.4 2.11E+09 1.50E+09 0.672 15 5.3E+03 3.8E+03 M12 7.7-12.1 4.4 1.01E+09 9.70E+08 0.648 14 2.5E+03 2.4E+03 M11 0-11 11 1.32E+09 1.19E+09 0.427 24 4.7E+03 4.2E+03 M9 4.4-12.1 7.7 1.71E+09 1.48E+09 0.648 15 7.3E+03 6.3E+03 M8 5.5-11 5.5 2.20E+09 1.78E+09 0.730 12 7.7E+03 6.3E+03 M7 n/a AVG 0.727 13 5.0E+03 ZONEM •D STDS 0.105 4 2.2E+03 Core depth zone length Area (cm2) Area (cm2) density LOI MSA-10 MSA-20 interval (cm) (cm) 10m bdy 20 m bdy (g/cm3) (%) (t) (t) M2 0-5.5 5.5 1.07E+09 8.94E+08 0.715 11 3.7E+03 3.1E+03 M3 0-5.5 5.5 1.31E+09 6.98E+08 0.916 7 6.2E+03 3.3E+03 M4 0-4.4 4.4 1.03E+09 8.53E+08 0.767 13 3.0E+03 2.5E+03 M5 0-6.6 6.6 7.77E+08 7.77E+08 0.628 14 2.8E+03 2.8E+03 M18 0-4.4 4.4 1.33E+09 8.79E+08 0.646 14 3.3E+03 2.2E+03 M1 0-3.3 3.3 8.65E+08 7.69E+08 0.558 15 1.4E+03 1.2E+03 M17 0-4.4 4.4 1.12E+09 1.06E+09 0.755 14 3.2E+03 3.0E+03 M16 0-5.5 5.5 1.04E+09 9.04E+08 0.694 14 3.4E+03 3.0E+03 M15 0-4.4 4.4 1.45E+09 1.37E+09 0.581 17 3.1E+03 2.9E+03 M14 0-4.4 4.4 1.17E+09 1.04E+09 0.585 17 2.5E+03 2.2E+03 M13 0-1.4 1.4 1.45E+09 1.03E+09 0.410 18 6.8E+02 4.9E+02 M12 0-7.7 7.7 2.10E+09 2.00E+09 0.504 20 6.5E+03 6.2E+03 M11 n/a M9 0-4.4 4.4 1.68E+09 1.45E+09 0.461 19 2.8E+03 2.4E+03 M8 0-5.5 5.5 1.09E+09 9.35E+08 0.586 19 2.8E+03 2.4E+03 M7 0-5 5 1.94E+09 1.39E+09 0.740 14 6.2E+03 4.4E+03 AVG 0.636 15 3.4E+03 STDS 0.132 3 1.7E+03 LAKE WIDE ZONE Total Total Bio Si C03 #of yrs MSAR-10 MSAR-20 MSA-10 (t) MSA-20 (t) (%) (%) ld-210 (t/yr) (t/yr) M-D 51536 42113 9.4 3.3 18 2499 2042 M-C 75391 62512 7.5 2.9 18 3751 3110 M-B 49633 40985 6.3 3.5 8 5597 4622 M-A 45912 36455 7.6 3.2 10 4094 3251 calculation to check bias of using three cores M-B 67673 6.3 3.5 8 7632 M-A 30048 7.6 3.2 10 2679 TE=95% TE=88% ZONE Yield-10 Yield-20 Yield-10 Yield-20 (t/yr/km2) (t/yr/km2) (t/yr/km2) (t/yr/km2) M-D 46 38 50 41 M-C 69 57 75 62 M-B 103 85 112 92 M-A 76 60 82 65 calculation to check bias of using three cores change M-B 141 2.84834 M-A 49 lake wide lake wide Zone depth span density LOI Bio Si # of years MSAR-10 MSAR-20 interval (cm) (g/cm3) % % (g/yr) (g/yr) K-C (a) 0-3.3 3.3 0.319 37 11.8 9 8.1E+03 4.5E+03 K-C (b) 3.3-5.5 2.2 0.306 37 11.8 10 4.7E+03 2.6E+03 K-B 5.5-9.9 4.4 0.268 38 14.2 23 3.3E+03 1.8E+03 K-A 9.9-22 12.1 0.287 36 13.9 125 1.9E+03 1.0E+03 K-C@C-C 0-8.25 8.25 0.298 37 12.9 34 4.9E+03 2.7E+03 K-B@C-B 8.25-12.1 3.85 0.262 38 14.1 21 3.1E+03 1.7E+03 K-A@C-A 12.1-19.8 7.7 0.279 37 13.9 69 2.1E+03 1.2E+03 K-A@M-A 10.45-12.1 1.65 0.275 38 13.9 10 2.9E+03 1.6E+03 K-B@M-B 8.8-10.45 1.65 0.260 38 14.1 9 3.1E+03 1.7E+03 K-B@M-C 5.5-8.8 3.3 0.280 38 14.2 17 3.6E+03 2.0E+03 K-C@M-D 0-5.5 5.5 0.313 37 11.8 19 6.3E+03 3.5E+03 168253 93366 9.4 MSAR- mass sediment accumulation rate Depositional area -10 m boundary (cm2) Depositional area - 20 m boundary (cm2) Mean carbonate content (%) Zone K-C (a) K-C (b) K-B K-A K-C@C-C K-B@C-B K-A@C-A K-A@M-A K-B@M-B K-B@M-C K-C@M-D TE=84% yield-10 (g/yr/km2) 3.9E+02 2.2E+02 1.6E+02 9.0E+01 2.3E+02 1.5E+02 1.0E+02 1.4E+02 1.5E+02 1.7E+02 3.0E+02 TE=84% yield-20 (g/yr/km2) 2.1E+02 1.2E+02 8.8E+01 5.0E+01 1.3E+02 8.1E+01 5.5E+01 7.7E+01 8.2E+01 9.4E+01 1.7E+02 TE=56% yield-10 (g/yr/km2) 5.8E+02 3.4E+02 2.4E+02 1.3E+02 3.5E+02 2.2E+02 1.5E+02 2.1E+02 2.2E+02 2.5E+02 4.5E+02 TE=56% yield-20 (g/yr/km2) 3.2E+02 1.9E+02 1.3E+02 7.5E+01 1.9E+02 1.2E+02 8.3E+01 1.2E+02 1.2E+02 1.4E+02 2.5E+02 247 Zone C-C depth cm zone Thiessen Area (cm2) density LOI-avg MSA MSA Core interval length (cm) 10m bdy 20m bdy avg g/cm3 % (t) 10 m (t) 20 m C1 0-6.6 6.6 1.15E+09 9.42E+08 0.391 25 2224 1827 C2 0-4.4 4.4 9.58E+08 7.37E+08 0.469 25 1489 1146 C3 0-6.6 6.6 6.56E+08 4.72E+08 0.435 25 1413 1018 AVG 0.432 25 1709 1330 STDS 0.039 0 448 435 Zone C-B depth cm zone Thiessen Area (cm2) density LOI-avg MSA MSA Core interval length (cm) 10m bdy 20m bdy avg g/cm3 % (t) 10 m (t) 20 m C1 6.6-8.8 2.2 1.15E+09 9.42E+08 0.368 26 688 565 C2 4.4-11 6.6 9.58E+08 7.37E+08 0.414 26 1943 1495 C3 6.6-11 4.4 6.56E+08 4.72E+08 0.421 26 902 650 AVG 0.401 26 1178 903 STDS 0.029 0 672 514 Zone C-A depth cm zone Thiessen Area (cm2) density LOI-avg MSA MSA Core interval length (cm) 10m bdy 20m bdy avg g/cm3 % (t) 10 m (t) 20 m C1 8.8-19.8 11 1.15E+09 9.42E+08 0.419 23 4076 3348 C2 11-16.5 5.5 9.58E+08 7.37E+08 0.434 24 1725 1328 C3 11-18.7 7.7 6.56E+08 4.72E+08 0.439 24 1683 1213 AVG 0.431 24 2495 1963 STDS 0.010 1 1370 1201 LAKE-WIDE lake wide lake wide zone-total zone-total biosi C03 # of years MSAR-10 MSAR20 Zone MSA-10 (t) MSA-20 (t) avg (%) avg(%) ld-210 t/yr t/yr C-C 5126 3991 9.4 7.2 34 126 98 C-B 3533 2710 10.8 7.7 21 137 105 C-A 7485 5888 9.0 7.3 64 98 77 TE=84% TE=84% TE=56% TE=56% yield-10 yield-20 yield-10 yield-20 Zone (t/yr/km2) (t/yr/km2) (t/yr/km2) (t/yr/km2) C-C 2.2 1.7 3.4 2.6 C-B 2.4 1.9 3.7 2.8 C-A 1.7 1.4 2.6 2.1 248 Appendix H Magnetic Properties of Terrestrial Materials Magnetic Susceptibility (Xo) and the SIRM/Xo ratio of terrestrial materials collected in each lake basin is presented. The first letter of the samples refers to the watershed, while the letter following the site number is to distinguish between samples taken at one site. Of the latter, those labelled as A, Bl, B2 or C refer to soil horizons. Watershed Sample Xo SIRM/Xo Material r/ym3/kel IK A/ml Tvne Clayoquot C5 0.125 2.4 bedrock,fine-grained, basic C8 0.415 2.3 bedrock, coarse-grained, acidic CIO 0.370 3.9 bedrock, medium-grained, basic Cll 0.276 1.8 bedrock, medium-grained, basic C12 14.0 5.2 bedrock, fine-grained, basic C16 0.094 48 bedrock, fine grained, basic C13 0.931 31 soil core C9 0.889 26 soil core CI 1.49 3.5 gravelly sand C15 0.884 22 gravel-fluvial C17 0.874 33 river bank material C18 0.511 18 clay-bank material C2 1.356 4.6 gravelly sand C7W 2.91 6.4 diamict-colluvium C7X 2.93 8.7 diamict-colluvium C7 Y 3.70 5.6 diamict-colluvium C7Z 3.37 5.0 diamict-colluvium Kite K2 39.3 0.5 bedrock, fine-grained, basic K3 C 0.055 1.5 bedrock, coarse-grained, basic K4 14.1 17 bedrock, medium-grained, basic Kl l Bl 1.24 24 soil on ? KI 1 B2/C 1.23 25 soil on ? Watershed Sample Xo SIRM/Xo Material IwrnVkel TKA/ml Tvne Kite K3 Bl 1.12 38 soil on rock K3 B2 0.929 39 soil on rock K5B1 0.951 43 soil on rock K5 B2 0.542 40 soil on rock K5 X 1.28 9.7 bedrock, medium-grained, basic K5 Y 0.054 1.2 bedrock, medium-grained, acidic K6B1 0.832 56 soil on clay K6 B2/C 0.731 55 soil on clay K6Z 0.093 19 clay K6b Bl 0.433 49 soil on rock K6b B2 0.381 59 soil on rock K7 Y 1.28 29 sand Maggie M10 5.97 1.6 bedrock, medium-grained, acidic Ml 3 0.072 1.1 bedrock, medium-grained, acidic Ml 4 13.676 11 bedrock, fine-grained, basic M16 1.33 2.4 bedrock, coarse-grained, acidic M20 3.29 1.4 bedrock, coarse-grained, acidic M21 0.075 39 bedrock coarse-grained, acidic Ml Bl 2.84 8.8 soil on granules Ml B2/C 1.74 12 soil on granules Ml C 1.68 8.3 granules M15B1 1.57 13 soil on rock M15B2 1.69 12 soil on rock M15B3 1.36 16 soil on rock M22B1 1.35 16 soil on rock M22 B2 1.64 15 soil on rock M22C 11.6 2.3 bedrock, coarse-grained, acidic M3B1 1.32 15 soil on diamict (till) M3 B2 1.77 15 soil on diamict (till) M3 C 1.99 14 diamict-till M4B1 1.25 11 soil on diamict (till) M4 B2/C 1.61 10 soil on diamict (till) M7B1 1.71 24 soil on diamict (till) M7 B2 1.79 18 soil on diamict (till) M7C 1.67 15 diamict-till M2X 0.367 15 diamict M8 2.09 45 laminated clays Watershed Sample Xo SIRM/Xo Material r,vm3/kel TKA/ml Tvne Toquart T6X 9.03 7.4 bedrock, fine-grained, basic T8X 0.166 1.0 bedrock, fine-grained, basic T9 Y 0.360 1.8 bedrock, fine-grained, basic TI A 0.400 21 soil on diamict (till) TI B 1.95 19 soil on diamict (till) TI B2 1.99 17 soil on diamict (till) TI C 1.87 29 diamict-till T2 Af 1.06 18 soil on rock T2B1 1.35 31 soil on rock T2 B2 1.07 26 soil on rock T5 A 0.887 18 soil on rock T5B1 0.476 19 soil on rock T5 B2 0.584 21 soil on rock T5 C 0.738 5.0 bedrock, fine-grained, basic T3 X 1.64 12 sand T3 Y 2.00 11 sand T3 Z 1.50 12 sand T4X 0.946 13 soil from road ditch T4 Y 1.56 19 gravel from road ditch T9B1 1.02 47 diamict-gully bank material T9B2 1.35 40 diamict-gully bank material T9X 1.87 37 gravels 


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