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Natural patterns and land use impacts on lacustrine sedimentation in Northwestern British Columbia Schiefer, Erik 1999

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N A T U R A L PATTERNS A N D L A N D USE IMPACTS O N LACUSTRINE SEDIMENTATION IN NORTHWESTERN BRITISH C O L U M B I A by ERIK SCHIEFER B.Sc. (Hons.), Wilfrid Laurier University, 1997 A THESIS SUBMITTED IN P A R T I A L F U L F I L L M E N T OF THE REQUIREMENTS FOR THE D E G R E E OF M A S T E R OF SCIENCE in THE F A C U L T Y OF G R A D U A T E STUDIES (Department of Geography) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH C O L U M B I A October 1999 © Erik Karl Schiefer, 1999 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 (j-COa / -« , | ) l y w The University of British Columbia Vancouver, Canada Date O C T . 6/ M l DE-6 (2/88) Abstract It has long been established that land use disturbances can induce elevated sediment yields in affected drainage basins. This effect is well documented with respect to forestry activities in the Pacific Northwest. A major problem encountered in studying disturbed sediment yields in the Pacific Northwest is putting the forestry impacts in context with the high degree of spatial and temporal variability in the sedimentary system. The analysis of lake sediments is an attractive method for assessing land use impacts on sediment yield at the basin scale, since a long term sedimentary record can be established that reflects all of the integrated upstream watershed effects. In this study, lake sediment records have been utilized to investigate historical sedimentation patterns in Northwestern British Columbia. Core chronologies and sedimentation rates were derived from 210Pb dating techniques. Study catchments have been selected that span a range of spatial scales, physiographic regions, and land use histories, in order to permit a comprehensive regional assessment of lake catchment sediment yield. Study objectives include the assessment of the natural patterns of lake sedimentation, determining the relative impact of forestry on lake sedimentation in context with the naturally observed variability, and the confirmation of lake coring and associated analysis techniques as appropriate methods of assessing land use disturbances. Specific sediment yield, or sediment yield per unit of contributing basin area, is used as an index of primary subareal denudation of the lake catchments. Specific yield in Northwestern British Columbia spans two orders of magnitude, from 0.0015 Mg/km2/day in the Interior Plateau to 0.1434 Mg/km2/day in the North Coast. The higher rates of sediment yield in the North Coast reflects the higher erosion rates, greater transport capacity, and lower storage potential in that region. Specific sediment yield also increases with increasing drainage area in the North Coast. This trend is likely associated with the dominance 6f secondary remobilization of Quaternary sediments from stream banks and valley bottom areas. In the flat-lying plateau and major valley areas specific sediment yield decreases with increasing drainage area, thus fitting the conventional model of sediment delivery where storage efficiency increases downstream. In the Hazelton and Skeena Mountains there is no significant relation between specific yield and drainage area. There is a clear trend towards increasing lacustrine sedimentation rates irrespective of land use change in the lake catchments. This natural trend is a major confounding factor in disentangling land use impacts on sedimentation patterns. This trend may be related to precipitation increases undergone in the whole study area over the last few decades. Natural disturbances, such as mass wasting and other geomorphic events, are important processes of sediment transfer in headwater lake catchments, although specific processes influencing lacustrine sediment yield were undetermined. Superimposed on. all of the observed natural variability are some qualitative and semi-quantitative land use effects on sediment yield. Land use impacts could only be partially separated from natural fluctuations, however, a clear land use signature, in the form of increased sedimentation rates, was observed in some of the study lakes. Most significant recent increases in sedimentation rates have occurred in the Nechako Plateau, Nass Basin and Major Valleys lakes which have been exposed to extensive forestry activities. Lake catchments which have been subject to multiple land use activities also showed a clear land use impact in the sedimentary signatures. Results indicate that lake sediment-based research can be an effective and useful approach to assess the long term impacts of forest harvesting and other land use disturbances on lake catchment yield. Inherent limitations of the lake sediment-based methodology and recommendations for future work are reviewed. iv Table of Contents Abstract ii Table of Contents iv List of Tables viii List of Figures ix Acknowledgements xi 1 INTRODUCTION 1 1.1 Problem Statement 1 1.2 Study Design 2 1.3 General Study Area 4 1.4 Thesis Overview 6 2 SEDIMENT TRANSFER AND LAKE SEDIMENT STUDIES IN THE PACIFIC NORTHWEST.. 7 2.1 The Sedimentary System.... 7 2.2 Impacts of Forestry on Sediment Transfer 9 2.3 Lake Sediment Studies 11 2.4 Discussion 15 3 METHODS 16 3.1 Introduction 16 3.2 Field Work 16 3.2.1 Lake Selection 16 3.2.2 Sediment Coring 17 V 3.2.3 Core Extrusion 19 3.3 Laboratory Analysis and Yield Calculations 19 3.3.1 210Pb Dating and Reconstruction of Historical Sedimentation Rates 19 3.3.2 Sediment Yield and Specific Yield Calculations 21 3.3.3 Varve Counting 22 3.3.4 Organic Content 23 3.3.5 Particle Size Analysis 24 3.4 GIS Database Development 24 3.4.1 Acquisition of Primary Landscape and Land Use Information 24 3.4.2 Lake Catchment Base Map Construction 25 3.4.3 Digital Elevation and Hydrologic Model Development 26 3.4.4 Refinement of Historical Land Use Information 27 3.4.5 Extraction of Landscape and Land Use Variables 28 3.4.6 Data Transformation 29 4 THE STUDY LAKES AND THEIR SEDIMENT RECORDS 31 4.1 Introduction 31 4.2 North Coast Region 31 4.2.1 Description of Study Area 31 4.2.2 Description of Study Lakes 34 4.2.3 Lake Sediment Records 35 4.3 Hazelton Mountains Region 39 4.3.1 Description of Study Area 39 vi 4.3.2 Description of Study Lakes 40 4.3.3 Lake Sediment Records 41 4.4 Skeena Mountains Region 48 4.4.1 Description of Study Area 48 4.4.2 Description of Study Lakes 48 4.4.3 Lake Sediment Records 48 4.5 Nass Basin and Major Valleys Region 51 4.5.1 Description of Study Area 51 4.5.2 Description of Study Lakes 51 4.5.3 Lake Sediment Records 52 4.6 Nechako Plateau Region 55 4.6.1 Description of Study Area.... 55 4.6.2 Description of Study Lakes 57 4.6.3 Lake Sediment Records 58 5 OBSERVED PATTERNS IN LACUSTRINE SEDIMENTATION 68 5.1 Introduction 68 5.2 Within-Lake Spatial Variability 68 5.3 Varved Sediments 69 5.4 Regional Variability.. 71 5.5 Temporal Variability...... 78 5.6 Impacts of Land Use 82 6 CONCLUSIONS 87 vii 6.1 Summary of Findings 87 6.2 Recommendations for Future Work 89 REFERENCES..... 92 Appendix A - Effects of Forestry on Sediment Transfer 103 Appendix B - Landscape Indices for Study Lakes 109 Appendix C - Land Use Summaries for Study Lakes 115 Appendix D - Sedimentation Rates and Land Use History 121 Appendix E - Sedimentation Rate Statistics 136 Appendix F - Maps of Study Lakes 137 Appendix G - Precipitation Data 159 V l l l List of Tables Table 3.1: Lake Catchment Base Map Layers 26 Table 4.1: Study Lake Classification 33 Table 4.2: Land Use Impacts of Selected Hazel ton Mountain Lakes 46 Table 4.3: Land Use Impacts of Selected Nass Basin and Major Valley Lakes 53 Table 4.4: Land Use Impacts of Selected Nechako Plateau Lakes 60 Table 5.1: Comparison of Sedimentation Rates Calculated from 210Pb Dating and Varve Counting 69 Table 5.2: Background Sediment Yield Regression and ANOVA Results 72 Table 5.3: Relations Between Disturbance Characteristics and Sediment Accumulation Rate Response.85 ix List of Figures Figure 1.1: Study Design 3 Figure 1.2: General Study Area 5 Figure 2.1: Conceptual Model of Drainage Basin Sediment Transfer 8 Figure 2.2: Expected Hydrologic and Sediment Transport Changes Following Timber Harvest 12 Figure 3.1: Log Transformation of Slope Data 30 Figure 4.1: Physiographic Regions and Study Lake Locatoins 32 Figure 4.2: Sediment Yield as a Function of Drainage Basin Area, North Coast Lakes 36 Figure 4.3:210Pb vs Varve Counting Sedimentation Rates for Toon Lake 36 Figure 4.4: Natural Disturbances in Lake Sedimentation, North Coast Lakes 38 Figure 4.5: Toon Lake Sedimentation Rates and Organic Content 38 Figure 4.6: Gordeau Lake 42 Figure 4.7: Aldrich - Dennis - McDonell Lake Cascade 44 Figure 4.8: Sediment Accumulation Rates (SAR) and Land Use for Aldrich, Dennis, and McDonell 45 Figure 4.9: Sediment Accumulation Rates (SAR) of Selected Hazelton Mountain Lakes 47 Figure 4.10: Sediment Accumulation Rates (SAR) for Damsumlo Lake 50 Figure 4.11: Sediment Accumulation Rates (SAR) for Beta and Farewell Lakes 50 Figure 4.12: Sediment Accumulation Rates (SAR) of Selected Nass Basin and Major Valley Lakes 54 Figure 4.13: Sediment Accumulation Rates (SAR) of Selected Control Lakes 54 Figure 4.14: Elizabeth Lake Sedimentation Rates, Land Use History, and Catchment Map 56 Figure 4.15: Sediment Accumulation Rates (SAR) of Selected Nechako Plateau Lakes 59 Figure 4.16: Pinetree - Boomerang - Doris - Tanglechain Cascading System 61 Figure 4.17: Binta Lake Catchment Map 63 Figure 4.18: Binta Lake Sedimentation Rates and Land Use History 64 Figure 4.19: Parrot Lake Sedimentation Rates, Land Use History, and Catchment Map 65 Figure 4.20: Takysie Lake Sedimentation Rates, Land Use History, and Catchment Map 67 Figure 5.1: Plot of Study Lake Depth and Effective Fetch with Critical Depth Limit (DT.A) 70 Figure 5.2: Comparison of 210Pb and Varve Counting Methods of Calculating Sedimentation Rates 70 Figure 5.3: Regional Differences in Specific Sediment Yield 74 Figure 5.4: Regional Differences in Mean Slope and Valley Flat Area of Lake Catchments 74 Figure 5.5: Specific Sediment Yield as a Function of Drainage Area 75 Figure 5.6: Specific Sediment Yield as a Function of Drainage Area Stratified Regionally 77 Figure 5.7: Natural Disturbance in Shea Lake Sedimentation 80 Figure 5.8: Total Annual Precipitation Cumulative Departure Plots 81 Figure 5.9: Separating Natural Trends and Land Use Impacts from the Sediment Records 84 Acknowledgements Special thanks are due to many people without whose help and support this research would not have been possible. I would first like to thank my supervisory committee: Brian Klinkenberg, my supervisor, for his guidance and helpful discussions throughout the duration of this project; Olav Slaymaker, for advice and enthusiasm towards the project; and Michael Church, for technical advice and constructive criticism. I would like to express my gratitude to FRBC and Ian Sharpe, M E L P Impact Assessment Biologist, for their foresight to initiate this project and continued guidance. Lisa Westenhofer, contract administrator, provided contract administration and liaison services with the Forest District Offices. I greatly appreciate the assistance of staff in the Forest District Offices of Bulkley/Cassiar, Morice, Kispiox, Kalum, North Coast, and Lakes District for their valuable insights which helped in the lake selection process and in reviewing mapping materials for accuracy. Specific individuals include Jim Schwab and Brian Grunewald, Bulkley Forest District; Loretta Kent and Sandra Shippit, Kalurn Forest District Office; Audrey Prevost, Kispiox Forest District; and Sarma Liepine, North Coast Forest District. The Ministry of Forests generously provided TRIM and FC1 data for the project, coordinated by Peggy Anderson of MoF Digital Data Sales. I would like to thank my industrial collaborators, Beak International and Geomatics International, for their valuable contributions. The following individuals contributed time to this project through discussions, reports, and field assistance: Kevin Reid and Richard Simms, industrial supervisors, for providing me the opportunity to work in close association with important BC consulting companies; Jamie Luce, for helpful discussions and brainstorming sessions; Alan Burt, for technical advice and field assistance; Lena Gomes, for helping me start the GIS database development; and Adam Cottrill and Paul LePage for field assistance. The efficient and timely delivery of quality work from Jack Cornet and Janice Lardner of Mycore Scientific for 2 1 0 Pb analysis is greatly appreciated. Thanks are due to Mike Treberg for his statistical advice and assistance. A special thankyou goes to my family for their motivation and continuing encouragement in my decision to undertake a Masters degree. Revisions by Brian Klinkenberg, Olav Slaymaker, and Michael Church greatly improved this manuscript. Financial support from the BC Science Council and my industrial collaborators is greatly appreciated. 1 1 INTRODUCTION 1.1 Problem Statement It has long been established that land use disturbances can induce elevated sediment yields in affected drainage basins (Goldberg 1971; Hudson 1995). This effect is well documented with respect to forestry activities in the Pacific Northwest. Increased sediment yields caused by forestry-related activities can have adverse effects on aquatic ecosystems in both streams (Scrivener et al. 1998) and lakes (Miller et al. 1997). Forestry-induced sedimentation has become a major concern in mountainous regions with high timber and fishery resources. Dominant processes, efficiency, and rates of sediment transfer vary greatly throughout the Pacific Northwest in response to topographic, geologic, and climatic factors (Swanson et al. 1987). Sediment transfer in mountainous regions is further complicated by significant geomorphic events that trigger major episodic pulses of sediment through the cascading sediment system (Trimble et al. 1995). The complex behaviour of sediment transfer in the Pacific Northwest holds profound implications in the study of forestry impacts on sediment yield. A major problem encountered in studying disturbed sediment yields in the Pacific Northwest is putting the forestry impacts in context with the high degree of natural spatial and temporal variability in the system. Although elevated sediment yields are commonly observed following road construction and timber harvest, the extent to which sediment is transmitted to downstream lakes has yet to be established. It has been demonstrated that the analysis of lake sediments can be an attractive method for assessing land use impacts on sediment yield at the basin scale, since a long term sedimentary record can be established that reflects all of the integrated upstream watershed effects (Arnaud 1997). This is especially beneficial in remote mountainous regions where stream gauging and long term monitoring is non-existent. In this study, lake sediment records have been utilized to investigate historical sedimentation patterns in Northwestern British Columbia. Study catchments have been selected that span a range of spatial scales, physiographic regions, and land use histories, in order to permit a comprehensive regional assessment of lake catchment sediment yield in Northwestern British Columbia. The specific project objectives are as follows: 1) Assess the natural patterns of lake sedimentation, including regional trends, spatial scale effects, and temporal variability. 2) Determine the relative impact of forestry on lake sedimentation in context with the naturally observed variability. 2 3) Confirm the usefulness of lake coring and associated analysis techniques as appropriate methods of assessing long term impacts of forest harvesting and other land use disturbances on lacustrine sedimentation. 1.2 Study Design The key premise of this study is that linkages exist between the inherent landscape characteristics and terrestrial disturbances (both natural and anthropogenic) of lake catchments and the quantity and composition of accumulating lacustrine sediments. Lake sediments represent a historical record of sediment yield and sediment characteristics from the contributing drainage basin area. When properly sampled and analyzed, the information which is recorded in the sediments can be retrieved in the form of sediment profiles which can be used to establish lake sedimentation patterns. Changes in sedimentation associated land use disturbance can be identified and described. The primary focus of this research is on the historical rates of lake sediment accumulation derived from 210Pb analysis of sediment core samples from the study lakes. 210Pb dating is a commonly used technique for establishing sediment chronologies back to 150 years before present. Other sediment parameters, such as organic content and particle size distributions, will also be measured for selected study lakes. A total of 70 lake catchments were selected for this study. The development and utilization of Geographic Information System (GIS) databases has been critical for handling the large amount of spatial data required for the project. A GIS database was developed to inventory the landscape data and land use histories of the lake catchments. Extracted from this database were variables to describe the natural landscape and the land use history for each study lake. These variables and the lake sediment data were then analyzed to resolve the three study objectives listed in the previous section. The project can be clearly divided into three phases: 1) Collection and analysis of lake sediment cores in order to establish historical rates of sediment accumulation and measure other sediment parameters for the study lakes. 2) Development of a spatial lake catchment inventory in a GIS environment suitable for the extraction of required landscape and land use indices for analysis. 3) Correlation analysis of GIS-derived indices with sediment accumulation rates and other sediment parameters in order to interpret regional sedimentation patterns. A schematic of how these project phases are integrated in order to address the research objectives is included in Figure 1.1. Other data sources, such as climate records and results from other studies, have 3 Figure 1.1: Study Design 1) Sediment Sampling and Analysis sedimentation other sediment rates characteristics cn* doolptkini SAR - not availabe for all lakes 2) GIS Database Development landscape land use variables variables CUTS Slop* 14 Elov 823 1 1 1. Dapth 6 ROADS WLA 344 1 1 . T Objective 1 - Assess the natural patterns of lake sedimentation, including regional trends, spatial scale effects, and temporal variability Objective 2 - Determine the relative impact of forestry on lake sediment yields in context with the naturally observed variability i 3) Data Analysis Objective 3 - Confirm the usefulness of lake coring and associated analysis techniques as appropriate methods of assessing long term impacts of forest harvesting and other land use disturbances on lacustrine sedimentation 4 been incorporated into the analysis when necessary. Detailed descriptions of the specific procedures and analysis techniques utilized in the study are included in later chapters of this thesis. 1.3 General Study Area The study area is situated in Northwestern British Columbia between 54° and 56°N and 126° and 131°W (Figure 1.2). Clague (1984) gives a detailed description of this region in a Geological Survey report on the Quaternary geology and geomorphology of the area. The study region mainly consists of rugged mountainous areas cut by deep valleys. Major rivers include the Skeena, Nass, Bulkley, Kispiox, and Babine. The Coast Mountains contains the most spectacular mountainous terrain in the study area. Other significant mountain ranges include the Hazelton and Skeena Mountains. Moving further to the east into the Nechako Plateau the terrain becomes more rolling with less exposed rock outcrops. A less extensive plateau area is located in the Nass Basin. The main valleys lie within the Coastal Western Hemlock and Sub-Boreal Spruce biogeoclimatic zones. Mountain Hemlock, Engelmann Spruce-Subalpine Fir, and Alpine Tundra zones become dominant at higher elevations. Most of the area below 1500m was forested prior to human settlement, but large sections of accessible valleys and plateau areas have been cleared during this century to support the forest industry and other land use activities. Topography and the predominant flow of moisture-laden air from the west control precipitation in the study area. In the Coast Mountains mean annual precipitation exceeds 2500mm, and locally is greater than 3500mm. The majority of the precipitation falls during the winter months during frequent mid-latitude cyclonic storms. There is a pronounced decrease in precipitation moving east from the Coast Mountains into the Interior Plateau region, where mean annual precipitation is only about 400mm. Temperature, like precipitation, is strongly influenced by topography. Winter temperatures in the study area decrease with increasing elevation and distance inland. At Prince Rupert on the coast (52m elevation), for example, a mean January temperature of about 1.8°C is much warmer than the -10.5°C mean temperature for Smithers (515m) in the Bulkley Valley. Temperatures at higher elevations are significantly colder during the winter months than those observed in low-lying coastal areas. Extreme winter temperatures are experienced at all elevations in the interior. Mean July temperatures in the main valleys are about 14-17°C, several degrees higher than on the mountain tops. All settlement areas are within the major valleys of the region. The principal urban centers include Prince Rupert, Terrace, and Smithers. The forest and fishery industries are the most important economic activities in the area, followed by agriculture, mining, and tourism. 5 6 1.4 Thesis Overview Chapter 2 includes background material on the effects of forestry on sediment transfer and lake sediment research. The chapter describes the natural sedimentary system, the effects of timber harvest and road construction on sediment transfer, and discusses the framework for lake sediment-based research of catchment disturbances. An extensive literature review of these topics is included for the Pacific Northwest region. Chapter 3 outlines all the procedures and methods used in this study, including field work, lab analysis, and database development. Chapter 4 describes the study lakes, their surrounding areas, and their sediment records. Chapter 5 summarizes observed patterns in lake sedimentation for Northwestern British Columbia, including regional, spatial, and temporal trends and land use impacts. The last chapter contains final conclusions and recommendations for future work. 2 SEDIMENT TRANSFER AND LAKE SEDIMENT STUDIES IN THE PACIFIC NORTHWEST 2.1 The Sedimentary System The Pacific Northwest is a diverse and highly active landscape. The region is defined as the coast mountains and intermountain areas of Northern California, Oregon, Washington, British Columbia and Southeast Alaska. The contemporary landscape is a consequence of the extraordinary tectonic history, glaciation, and subaerial denudation during the Pleistocene (Clague and Mathews 1993). Landscape evolution continues today by mass wasting of unstable valley slopes and fluvial erosion of Pleistocene deposits down valley. Processes and rates of sediment transfer are highly variable because of the wide range of topographic, geologic and climatic factors throughout the region (Swanson et al. 1987). The storage reservoirs and fluxes of sediment through a drainage basin define a cascading system that is linked to the physical form of the basin. Based on conservation of mass, a sediment budget can be constructed for a catchment, which allows us to make inferences about the relations between various transport and storage processes. Sediment budgets provide a framework for quantifying rates of sediment production, transport, and deposition throughout the drainage basin (Dietrich el al. 1982). A conceptual model of sediment transfer in British Columbia is presented in Figure 2.1. The model is based on the sediment budget work of Roberts and Church (1986) in the Queen Charlotte Ranges and Jordan and Slaymaker (1990) in the Lillooet River Basin. Catchments subject to active glaciation or volcanic disturbances would require additional terms in the sediment transfer model. This model provides a framework for estimating basin response to erosional changes invoked by land use disturbances. Sediment sources include glacial deposits, organic material, and bedrock, with the former being dominant for many drainage basins in British Columbia. Through weathering, erosion and mass movement, sediment reservoirs accumulate and some sediment is transported down hillslopes and into -. valley margins. Episodic mass wasting events are the dominant geomorphic process of sediment transport for most mountainous watersheds. Surface erosion is generally insignificant in forested watersheds, except on recently exposed landslide scars. Sediment that reaches the valley footslopes or becomes a proximal channel deposit is then subject to fluvial transport processes. Depending on the sediment caliber, channel characteristics, and hydraulic regime, sediment is either transported in suspension through the drainage network, in traction on the channel bed, or enters into the cascade of valley bottom sediment reservoirs. Very fine material (fine sand and finer), which is focused on in this study, is typically washed efficiently through the system. Sediment sinks include inactive alluvial valley fill and delta or lake bottom sediments. Sediment yields are highly variable, both temporally and 8 Figure 2.1: Conceptual Model of Drainage Basin Sediment Transfer Glacial Deposits Organic Material Weathering Bedrock I Rockfall Frost Shattering Rock Slide Debris Slide In Situ Soil Soil Creep Surface Wash Bank Erosion Alluvial/Debris Flow Fans and Terraces t Colluvium Landslide Deposits Debris Flow Debris Slide ______ Fluvial Transport Channel Deposits (active) Fluvial Transport Sedimentation Delia, Lake Bottom Sediments (inactive) I l-'loodpluin/Tcrrucc Deposits (IL-.S'n active) Bank Erosion V Alluvial Valley (iiincliu') Suspension (very fine sediments) T Storas; Process Transport out of catchment Sources: Jordan and Slaymaker (1990) Roberts and Church (1986) CO CD o e 3 £ (E. § 5' P" cn — O _ o. — 5 a CD _ o 1— 2 < 9. != ^ CD* o & < 3 EL sr B cn O 3 9 o 3 00 CD p. CD 3 3 9 spatially, in mountainous watersheds. Sediment transfer is further complicated by the transport of sediment through the drainage basin in solution. Although significant in terms of total volume, the solute load has not been investigated in this study because of practical constraints. 2.2 Impacts of Forestry on Sediment Transfer Forestry is a major economic activity for the Pacific Northwest region. Significant research has been carried out in order to investigate the relations between forestry activities and processes of sediment transfer in the Pacific Northwest. A comprehensive review of this literature has been compiled for this thesis. The references retrieved in this review have been tabulated in Appendix A. Included in the table are the research authors, location of the study, codes for the approach and scale of the study, and brief descriptions of the land-use treatment and the study findings. The classifications used to define the approach and scale of the studies are based on the classification system devised by Reid (1993). Most of the research has been conducted in Oregon, followed by Northern California and Washington, for the US Forest Service. A few studies focusing on mass wasting have been completed in Southeast Alaska. Many studies in British Columbia have been motivated by concerns over the effects of forestry on fishery resources. The two major projects in British Columbia are the Carnation Creek Experimental Watershed on Vancouver Island and the Fish/Forestry Interaction Program on the Queen Charlotte Islands. Limited research has been conducted in other regions of British Columbia. No substantial research projects on sediment transfer have been undertaken in Northwestern British Columbia. Results from the reviewed research reflect the high degree of variability in sediment production and transport in Pacific Northwest watersheds. Differences in topography, geology, climate, extreme event occurrences, scale of study, disturbance type and intensity, and research methodology all make the generalization of findings difficult. No significant attempt has been made to stratify this large volume of research available for the Pacific Northwest region. By reviewing the research, however, some significant relations and trends can be identified. With very few exceptions, a positive correlation existed between land use treatments and the measured sediment transfer parameters. In almost every study, forest roads were identified as the most significant anthropogenic source of sedimentation, usually by increasing landslide frequency and fine sediment production. The timber harvesting technique and the type of road surface and traffic density all influence sediment production rates from disturbed areas. Basin responses commonly lag the forestry treatments, often being triggered by storm events some time following the land use disturbances. In most cases sediment production and transport rates return to background levels within a few years of the peak response. The occurrence of episodic events has clearly limited the effectiveness of small sample and short-term studies to determine long-term land use impacts on sediment transfer. Study results show that landslide volumes increase above undisturbed levels by 3-31 times in 10 harvested areas, and 10-87 times in roaded areas. Forestry-induced mass wasting is generally the greatest concern for land managers. Downstream sediment yields are commonly elevated many times above their background levels, depending on the extent of land use disturbance. Observed increases of sediment yield ranged from 0 to 109 times undisturbed levels. Sediment concentrations following road construction can be increased up to 100 times the undisturbed levels during high precipitation events. There are many processes through which timber harvest and forest road development influence sediment production and transport. Timber harvesting on channel banks and through streambeds releases large volumes of sediment into the drainage network by directly altering the bed and bank morphology of the stream channels. This type of harvesting is now atypical in the Pacific Northwest. The erosional effects of timber harvesting is best understood by looking at how the hydrologic parameters of the harvested area are altered, since the presence and movement of water is the dominant forcing function of sediment transfer processes. Removal of forest cover affects forest hydrology in many ways. There is a large volume of literature available that addresses the effects of forestry on hydrology (see Wilford (1975), Bosch and Hewlett (1982), Reid (1993), and Whitehead and Robinson (1993) for literature reviews). With forest removal, most transpiration ceases until new vegetation occupies the area. Total evaporation also decreases because canopy interception is greatly reduced. The reduced evapotranspiration makes more water available for percolation through the soil to recharge the groundwater reservoir. Higher soil moisture, combined with the decreased tree root strength following the removal of vegetation, leads to a higher frequency and severity of mass wasting events. The increased soil moisture storage also reduces the capacity of the soil to accept additional rainfall input, resulting in increased surface runoff and erosion. Timber harvest can also affect the infiltration capacity of forest soils because of associated soil compaction or soil exposure followed by the erosion of the topsoil. Removal of the forest's foliage greatly increases the severity of erosion by raindrop impact. Snow accumulation and the rate of melt are increased in cleared forest areas because of decreased canopy interception and increased site exposure. Streams downstream to harvested areas tend to have higher peak flows because of the modified hydrologic characteristics of the contributing basin. This increases the capacity of streams to entrain and transport sediment down valley during high flow events. The overall effect of timber harvest on hydrology can be summarized as a simple water balance equation, shown below. Since timber harvest reduces canopy interception and evapotranspiration, a greater proportion of the precipitation input becomes surface runoff, interflow to streams, and stored as ground water, all of which positively contribute to sediment transfer processes. Note that responses can lag timber harvest because thresholds for erosion and mass wasting may only be exceeded during large magnitude precipitation events that occur in conjunction with the necessary antecedent hydrologic conditions. 11 precipitation = canopy interception + evapotranspiration + runoff + interflow + ground water reduced by timber harvest contribute to erosion and mass wasting The timber harvest/hydrology/sediment interactions are summarized in Figure 2.2 (Source: Cassells, Hamilton, and Saplaco 1983). The diagram illustrates some expected basin responses to timber harvesting. Actual responses are difficult to predict because of the complex interactions between processes and the large number of variables involved. Geomorphic thresholds, stochastic processes, and cumulative watershed effects, also increase the difficulty in predicting responses to timber harvest. Hydrologic modifications associated with forest road development can also significantly affect drainage basin sediment transfer. Road development accompanies most land-use activities, but is most commonly associated with forestry. Road construction involves the removal of vegetation and soil compaction, resulting in similar hydrologic effects as timber harvesting. There are some additional hydrologic impacts of forest roads that need to be considered in the study of drainage basin sediment delivery. Forest roads affect subsurface flow by intercepting the water at the cut slope and channeling it down ditches and roadways as surface runoff. Water emerges from the cut bank when soil becomes saturated or piping failure develops. These conditions lead to high instability of the cut bank, where failures are common. Roads that fill stream channels or that have been constructed with inadequate culverts can cause ponding and diversion of surface flows. Ponding of water leads to seepage through the road fill and an increase in the pore water pressures, which can result in road fill failures. Diverted surface flows can follow ditches, cross the road surface, or flow down the road surface. Roads that tend to follow hill contours cause less drainage diversion then roads with a dendritic topology. Water diverted over road surfaces causes fill erosion and gully development, with the stream attempting to regain its previous stream gradient. In some cases, runoff can be diverted into new courses. This can lead to extensive erosion and the initiation of slope failure. In extreme cases, when road densities are high relative to the natural drainage density of the landscape, forest roads can dominate the sediment delivery of a drainage basin (e.g., Brownlee et al. 1988, Best et al. 1995). 2.3 Lake Sediment Studies The lake catchment is a logical extension to the terrestrial drainage basin unit. Lakes act as major storage sites in the cascading sediment system of drainage basins. The trap efficiency of a lake is a function of the lake size and shape, location of inflows and ouflow, volume of water throughput, and the character of the sediment. The quantity and quality of lake sediments reflect the interacting watershed processes above the point of inflow, as well as internal lake processes (Petts and Foster 1985). It is reasonable to expect that anthropogenic modifications to the sedimentary system could be recorded in 12 O to 1- — o •a c •a o g CO cd CD U . O fi h-1 4—» O o u <u U 00 e -a u u u str 3 str T3 CD cd <U fi <2£ S T3 _o u o 3 o U inte B « s 4) 3 1 / 1 -S cd O CD cd <-> £ s I cd " u u ^ c > £ t: 3 00 cd o o co CU J = ti 00 3 *p co 'o s B _o 'co 0) O CO U i cd CD 2i o o fi «2 1 3 60 B T3 .2 1) co 2 o cd u. p CD CJ c S 60 fi ase CO cd a o ed •a s CU o U i 00 Is l-l CD JS Hig T3 & U o CO f—H cd « cu fi S I I—I co CD B B cd J3 fi CJ _o T3 'c/l CD O CO u cd o <u u, o B »—l I 13 downstream lake sediments. It has been proposed that lake sediment-based studies can be highly effective in the study of land use impacts on sediment yield. Petts and Foster (1985), Foster et al. (1987) and Foster et al. (1988) have reviewed and demonstrated the lake sediment framework and its application in reconstructing past catchment conditions associated with land use disturbances. Analyses of accumulated lake sediments can obviate some of the major limitations of drainage basin studies of land use disturbance. Since lake sediments are a record of historical lake catchment conditions, an appropriate time scale of system response and recovery can be selected, and background conditions and long term trends can be established. Another advantage of this approach is that it addresses the sedimentary system at the basin scale, thereby inherently taking into account the cummulative effects of all interacting processes within the catchment, which are usually difficult to predict (Arnaud 1997). Interpretation of land use effects in the lake sediment signature must account for intermediate sediment storage sites in the catchment, such as other upstream lakes, wetland areas, and valley flats. Lake sediment studies must also account for non-catchment derived sediment sources, sedimentation processes occurring within the lake, and natural fluctuations in the sediment transfer processes. Furthermore, many practical problems exist in the recovery and analysis of lake sediments. The most comprehensive review of lake sediment sampling and analysis can be found in the Hakanson and Jansson (1983) lake sedimentology text. Despite these difficulties, it has been argued that the lake sediment approach of studying land use effects on sediment yield is a powerful methodological framework for testing conceptual models and evaluating complex response-recovery relationships at an appropriate time scale (Foster et al. 1988). Most Pacific Northwest research on the impacts of land-use on sediment transfer has been focused on hillslopes and in stream channels. The majority of sediment-based research in water bodies is concerned with accelerated sedimentation of reservoirs for the purpose of engineering predictions for reservoir project design and operation. There has been little research on the effects of land use on sedimentation patterns in natural lakes. Lake sediment-based studies of land use disturbances have been reviewed for the Pacific Northwest and are reported on below. Lake Washington, to the east of Seattle, has been the site of some early lake sediment research studies. Using X-ray photography of sediment cores, Edmondson (1969) showed that eutrophication caused by the growth of Seattle is recorded in the upper layers of the sediment. Fossil pollen evidence in the lake sediments was shown to reflect the vegetation disturbance caused by forestry and agriculture surrounding Lake Washington by Davis (1973). In Lake Whatcom, Orme (1990) used X-ray analysis and radio-carbon dating of sediments in conjunction with other historical records to investigate the reoccurrence of debris production under coniferous forests in northwest Washington. That record 14 indicated that major debris production in the basin over the past 3400 years is a recurrent process. The record also suggested that the magnitude of debris production is not significantly altered by timber harvesting alone, but may be locally accentuated by slope failures associated with forest roads. Chemical and physical analysis of sediments from Devils Lake, located in central Oregon, was used to detect recent limnologic change by Eilers et al. (1996). Results showed that the lake had been productive prior to recent development. Sediment accumulation rates based on radiometric dating with 2 I 0Pb indicated a major erosional event occurred in the early 1900's, causing a 5-fold increase in the accumulation rate. Rates returned to pre-1900 levels but then increased again in the last several decades, coinciding with intense storm periods and early development activities. The most recent increases observed in the record were attributed to the combination of urbanization and logging in the lake catchment. Some interesting studies on the effects of land use on lake sediments have been conducted in British Columbia. A suite of lake sediment analysis techniques were used by Arnaud (1997) to assess the effects of forestry on lacustrine sedimentation in four lakes on the west coast of Vancouver Island. The results indicated that increases in sediment yield coincided with forestry activities, as well as natural disturbances and other human activities. The study demonstrated that the lake sediment approach may be useful in monitoring the effects of forestry activities, although the sedimentary signature may be confounded by other catchment disturbances. Arnaud (1997) reviewed some important limitations of current lake sediment analysis and its application to forestry research. Precise chronological control, rigorous sampling strategies, and careful choice of analysis techniques, were all identified as important factors for successful lake sediment research. Pack et al. (1997) applied 210Pb dating to determine sediment accumulation rates to assess relative sedimentation impacts in Trout Lake, southern British Columbia. Variables describing the extent of land use activities were back calculated from a GIS database of the Trout Lake catchment area. These land use variables were correlated with relative changes in sediment accumulation rates derived from 210Pb dating. A relation was noted between sediment accumulation rates and the magnitude of forest road construction, especially the amount of road construction on erodible soils within 100 meters of streams. Sediment pulses lasting for 5 to 7 years with accumulation rates 10 times greater than background coincided with the observed anthropogenic disturbances in the lake catchement. Small-sediment based research studies have been carried out on two lakes included in this study. Maclean (1983) used sediment core samples to assess the water quality of Aldrich Lake, located in the Hazelton Mountain Range. Highly elevated levels of metal contamination caused by mining activity were observed in the sediment samples. Reavie and Smol (1996) investigated recent eutrophication concerns of Takysie Lake, located in the Nechako Pleateau. A study of algal remains (especially diatoms) and 210Pb dating of a sediment core showed that forestry, agriculture, residential settlement and recreational 15 use of the lake, resulted in slight increases of nutrient loading and notable increases in sediment accumulation. 2.4 Discussion The natural sedimentary system, the effects of land use on the system, and lake sediment-based research were reviewed for the Pacific Northwest in this chapter. Included was a comprehensive review of research on forestry impacts on the sedimentary system and lake sediment research on land use disturbances. Increased sediment transfer down hillslopes and through stream channels following forestry activities has been well documented. There has been little research to date on the direct effects of forestry activities on lacustrine sedimentation. Other than a couple of small, single lake sediment assessments, there have been no significant research projects on land use effects on sediment transfer undertaken in Northwestern British Columbia. A common difficulty in previous research in other regions has been the establishment of appropriate time scales of study to determine background conditions, natural variability, and long term trends in the sediment transfer processes. Another common problem experienced in many studies has been the inability to deal with the high degree of spatial variability and inherent complexity of sediment transfer at the drainage basin scale. It has been proposed that lake sediment-based research could preclude many of these difficulties. All reviewed lake sediment studies on land use impacts in the Pacific Northwest showed some form of disturbance signature in the sediment record. Although these results are encouraging, significantly more research is necessary to better establish this connection. Lake sediment-based studies on the effects of forestry on lacustrine sedimentation by Arnaud (1997) and Pack et al. (1997) are important precursors to this study. Both of these studies showed that lake coring and associated analysis techniques can be useful and appropriate methods of assessing long term impacts of forest harvesting and other land use disturbances on lacustrine sedimentation in British Columbia. This project will take advantage of some of the recent lake sediment analysis techniques reviewed and demonstrated by Arnaud (1997) in her study of forestry impacts on lacustrine sedimentation on the West Coast of Vancouver Island. The general methodology will follow that of Pack et al. (1997) in the assessment of relative sedimentation impacts of Trout Lake Basin, British Columbia. The project varies chiefly in that a large collection of lake catchments are being incorporated into the impact analysis, as opposed to just a single catchment. This has allowed us to investigate how different drainage basin morphologies and different land use disturbances are reflected in the lake sediment signatures, and has provided insight into the regional patterns of lake sedimentation in Northwestern British Columbia. Specific methodologies used in this study are discussed in the following chapter on study methods. 16 3 METHODS 3.1 Introduction Study methods and techniques used in this research project are presented and discussed in this chapter. The chapter is divided into three components: field work, laboratory analysis, and GIS development. Reviewed in the field work component are the procedures used for lake selection, sediment coring, and the extrusion (or sub-sampling) of the sediment cores. Historical profiles of lake sediment accumulation rates, derived from 210Pb dating of the lake sediment samples, is the primary result of the laboratory analysis. Subsequent laboratory analysis, including varve counting, organic content measurements, particle size work, and other analysis, has provided additional information to further supplement the sedimentary database for selected study lakes. A GIS database was developed in order to inventory the lake catchments in this study. Output from the GIS database were indices which were used to describe the natural landscape characteristics and land use histories of the lake catchments. Results from the laboratory analysis and the GIS outputs are reviewed in the discussion of the study lake catchments and their sediment records in the following chapter. 3.2 Field Work 3.2.1 Lake Selection The Ministry of Environment, Lands and Parks provided a preliminary list of several hundred potential headwater study lakes for this project. They required that lakes had to be included from the North Coast, Kalum, Kispiox, Bulkley, Morice, and Lakes Forest Districts, and that the research dovetail the ongoing lake inventories that were being conducted concurrently by the Ministry of Fisheries in the study area. Topographic maps, lake inventory reports, and air photos of the region were examined in order to reduce the list of candidate lakes. Site selection involved consideration of lake suitability for a sediment-based sediment yield study based on lake morphometry and landscape characteristics of the lake catchment. Lakes had to be deep enough (preferably 10+ m) to minimize the potential for physical reworking of sediments from waves, seasonal overturn processes, lake level fluctuations, subaqueous slumping, and biotrubation by bottom dwelling organisms (Dearing and Foster 1986). Lakes also had to be large enough to be accessible by floatplane and small enough that a single core represents a fair and consistent index of sediment yield to the lake (approximately 1km2). Complex bottom morphology leads to greater within-lake spatial variability of sedimentation patterns, making estimates of sediment yield using a single core unreliable. Lakes likely to have a well defined, singular, steep-sided basin were identified by the degree of crenulation of the lake shoreline (Hakanson and Jansson 1983). Both 17 landscape and land use characteristics of the lake catchments were considered in the lake selection process in order to ensure that the study lakes were well representative of lakes in Northwestern British Columbia. First to third order catchments were selected from a variety of physiographic regions in the study area, including coastal, mountainous, plateau, and major valley regions. Unforested high-alpine and glacier lakes were not included in this study. Significant effort was also made to include lakes subjected to a gradient of forestry-related land use disturbances. Ultimately, field reconnaissance was used to determine the final list of study lakes. A total of seventy small lake-catchments (order of 10 to 100 km2) were selected for the project. Most lakes were accessed by float plane because of the lack of road accessibility and due to the large distances between study lakes. A few lakes that were conveniently road accessible were sampled using a small portable boat. 3.2.2 Sediment Coring Coring of lake bottom sediments using a modified Kajak-Brinkhurst (KB) gravity corer was a major component of the field work. The KB corer uses a triggered plunger to seal the top of the core barrel allowing extraction of cores without the use of a core catcher, preventing the alteration of the outer surface of the core (Stephenson et al. 1996). The corer consists of an upper head assembly, which includes the trigger mechanism, the plunger, and the thread-in for the core tube metal sleeve. The trigger mechanism includes a spring which provides tension on the trigger arm, maintaining the plunger in place until released by a messenger. The core tube metal sleeve attachment is available in several lengths depending upon the length of core tube required. Weight attachments were not required in the extraction of the soft, organic-rich sediments in the study lakes. The core tubes consisted of clear acrylic tubes (2 inch inner diameter) cut to one meter lengths. Care was taken to ensure that the ends were cut smooth and perpendicular to the tube length in order to permit a good seal during the extrusion of the sample. A more detailed description of the KB corer and various other coring devices is provided by Brinkhurst (1974). Upon arrival on each of the study lakes, an exploratory depth sounding run was conducted along the entire length of the lake using an Eagle River Depth Sounder equipped with a strip chart recorder. Sediment sampling sites were always situated at the deepest point of the lake basin. Sediment cores retrieved from deep and stable sections of the lake bottom usually have the finest stratigraphic definition as a result of sediment focusing of the fine materials (Pack et al. 1997). Deep basins may accumulate material up to twice as fast as the average for the whole lake. Therefore, cores retrieved from these regions should provide the best natural temporal resolution. Also, the sediments in the deepest point of the lake are less likely to be resuspended or reworked by wind mixing, lake/river currents or subaqueous slumping. Sampling locations were identified using existing bathymetric maps (where available) as 18 confirmed by echo sounding. The echo sounder alone was used to locate sites where mapping was not available. Sampling location coordinates were identified and recorded via GPS fixes. Once the sampling location was determined, the plane or boat was anchored at the bow and stern to minimize movement during sampling. In preparing to use the KB corer, the steel outer sleeve was securely threaded into the head piece to ensure an air tight fit. A clean core tube was slipped into the sleeve and secured with duct tape. The upper end of the plunger rod was then inserted into the trigger mechanism and the corer lowered to the bottom using a rope attached through the head piece. A stainless steel messenger was attached onto the rope prior to the lowering of the corer. The sampler was lowered at a controlled rate in order to avoid disturbance of the sediment by a bow wave. Tension had to be kept on the line at all times to ensure that the sampler remained vertical and to prevent knotting in the rope that would impede the passage of the messenger. Once the sampler was inserted into the bottom, the messenger was released. The sampler was then retrieved after the plunger mechanism was released. This was done by smoothly retrieving the line by hand, avoiding jerks, twisting and tilting. This helped in reducing the loss of material from the bottom of the core and reduced the mixing of the upper loose layers of sediment. When the sampler was near the surface a rubber bung was inserted into the bottom of the core tube. The sampler was then retrieved into the boat, the securing tape and sleeve were removed, and the corer lifted off from the sediment core tube. A cap was attached to the top of the core, with any trapped air allowed to escape to minimize any subsequent disturbance of the core during transport. After the core had been removed from the corer, the sample was visually inspected to check for the following: 1) The sampler was not over-inserted into the bottom. This may be obvious if the sediment is all the way to the top of the core or if the overlying water is murky with stirred up sediment. The top of the sediment should be relatively loose, with the possibility of some obvious layering (varves). In addition, there may be evidence of overlying algae, the presence of oligochaete or chironomid cases or even some pelagic organisms (Chaoborus or amphipods) in the overlying water which v/ould indicate an acceptable core. 2) The sediment-water interface is intact with no sign of channeling or sample washout. 3) The desired depth of penetration has been achieved. 4) There is no evidence that the core sampler was inserted on an angle or tilted on retrieval. If the collected core sample failed any of these criteria then the sample was discarded and another sample collected at the same site. The location of consecutive attempts should be as close together as 19 possible to ensure that the sample sediment is as similar as possible. The sampler was cleaned prior to the collection of each sample to prevent the contamination of the next sample. Once an acceptable core had been retrieved, it was useful to mark the rope to ensure accurate insertions in subsequent cores. A total of four cores were collected at each station, with one each for dry bulk density analysis, 210Pb dating, archiving, and a backup in case of loss. After all of the cores were collected, they were aligned to ensure that they were consistent in term of apparent layering and other sediment characteristics. The cores were then secured together with duct tape to help ensure that they remained vertical during transport. As time permitted, additional cores were sampled at a variety of other mid-lake locations. These cores were visually inspected to examine the areal continuity of the lake bottom sediments. 3.2.3 Core Extrusion Prior to the extrusion of the core samples, the cores were inspected visually and photographed for future reference. Core extrusion and slicing was performed using the OPS Core Extruder. This extruder uses water pressure from a pressurized tank to push the sediment core bung and the sediment sample up the core tube, which is mounted vertically in the extruder. A hand-operated valve was used to control the water pressure and accurately extrude the required core intervals. A sliding sectioning device was used to slice off sediment samples from the top of the core. The core sub-samples were then washed into pre-labeled sample bags using distilled water. Excess air was removed from the sample bags, which were then sealed, and packed for transport out of the field. The top 10cm of sediment was generally deep enough to capture about 100 to 150 years of sediment accumulation, the limit of 210Pb dating. 'The top 10cm of the core were extruded at 1cm intervals. The remainder of the core was extruded at larger intervals (2-5cm) to ensure sub-sampling through to background levels. Cores were extruded for dry bulk density analysis, 210Pb analysis, and archiving for additional sediment analysis. The smear zone of the 210Pb samples was removed to avoid contamination caused by the penetration of the core through the lake sediments. This was accomplished by removing the outer 2 to 3mm of the core segment with a clean, sharp, stainless steel implement before transferring the slice into the sample bag. Additional notes were made of the sediment character and layering structures throughout the extrusion process. 3.3 Laboratory Analysis and Yield Calculations 3.3.1 2 1 0 P b Dating and Reconstruction of Historical Sedimentation Rates 210Pb dating is a widely used technique for establishing lake sediment core chronologies (e.g. Appleby and Oldfield 1977; Appleby et al. 1977; Evans and Rigler 1980; Bloesch and Evans 1982; Appleby and Oldfield 1983; Battarbee etal. 1985; Binford etal. 1993; Arnaud 1995; Blais etal. 1995; 20 Eilers etal. 1996; Pack et al. 1997). 210Pb is a naturally occurring radionuclide in the 2 3 8 U decay series. The 210Pb in lake sediments is derived from the following sources: 1) In situ decay of 2 2 6Ra (an intermediate isotope in the 2 3 8 U decay series) supplied to lake sediments as part of the particulate erosive input. 2) Direct atmospheric fallout into the lake, which is scavenged by sediment particles and deposited on the bed of the lake. 3) Indirect atmospheric fallout entering the lake via the lake catchment. 4) 2 2 6Ra decay in the water column delivered into the lake sediments by diffusion. 210Pb formed by the decay of radium (source 1 above) is termed the "supported 210Pb" and is in radioactive equilibrium with the radium. The 210Pb activity in excess of the supported component (sum of sources 2, 3, and 4 above) is called the "unsupported 210Pb". The principle source of the unsupported component is direct atmospheric fallout (source 2 above), since the other unsupported sources are usually considered to be negligible. The unsupported 210Pb decays exponentially in time in accordance with its half-live (22.26 years). It is this radioactive decay process that provides the basis for dating sediments using 210Pb. The 210Pb analysis and reconstruction of historical sedimentation rates for the project was conducted by Jack Cornett of MyCore Scientific Limited. 210Pb activity was measured by the radiochemical purification of its granddaughter isotope 210Po. Details of this procedure are presented in Evans and Rigler (1980) with modifications described in Cornett et al. (1984) and Rowan et al. (1995). The concentrations of 210Pb were interpreted using the constant rate of supply (CRS) dating model (Appleby and Oldfield 1979; Robbins 1978). This model is generally preferred over other interpretation techniques because it allows for fluctuating rates in sediment deposition over time. 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. The total quantity of excess 210Pb (calculated by numerical integration of the 210Pb profile) is used in the determination of sediment ages and sediment accumulation rates. The age of a sediment core section is calculated using the following formula: Age = Age(0)-k"'-ln(S/Si) 21 Where: Age is expressed in years Age(O) is the year that the core was collected k is the decay constant for 210Pb in years S is the total quantity of excess 210Pb in the core Si is the quantity of excess 210Pb below depth (i) Since the quantity of excess 210Pb decreases exponentially with time, the uncertainty in the calculated sediment age is greater for older sediments. The 95 percent confidence interval for "!10Pb dates ranges from about ±2 years at 10 years of age, ±9 at 100 years, and ±22 at 150 years old (Binford 1990). The rate of sediment accumulation in a section was calculated directly using the following formula: Sedimentation Rate = (k-Si)/(Q-A) Where: Sedimentation rate is expressed in grams of dry weight per square meter per year C; is the concentration of excess 210Pb in the section (calculated using bulk density) A is the area of the core in meters Using the calculated age and rate of sediment accumulation for the core sections, profiles of historical lake sedimentation rates at the sampling site can be developed. These have been included for all the study lakes in Appendix D. Sedimentation rates are best represented as horizontal lines plotted over core section intervals since the rate is an averaged measure across each section. Using this graphical representation, background lake sedimentation rates were estimated. The background accumulation rate is assumed to be the component of the sediment load derived from primary denudation processes. The estimation was done visually by discounting outliers and fluctuations in sedimentation rates that are likely associated with watershed disturbances or dating errors/uncertainty, leaving a constant background accumulation rate. The estimated background sedimentation rates are indicated by a dashed line in the study lake profiles in Appendix D. These background rates and other sedimentation rates statistics are also compiled by lake catchment in Appendix E . 3.3.2 Sediment Yield and Specific Yield Calculations Sediment yield is defined as the total sediment outflow from a drainage basin in a specified period of time (Vanoni 1975). The study of sediment yield is common in geomorphic literature because it can be used as a measure of the aggregate effect of contemporary and palaeogeomorphological processes of drainage basin weathering and erosion (catchment denudation) and, furthermore, to assess 22 anthropogenic influences on these processes (Owens 1988). Background sedimentation rates derived from 210Pb dating can be multiplied by lake area to obtain an index of total sediment yield from the contributing lake catchment area. The assumptions of areal continuity (the measured sedimentary property should be deposited in similar proportions to other sedimentary constituents over the whole lake bottom area) and synchroneity (once deposited, the measured property should be persistent and immobile) must be met for the calculated sediment yield to be a fair and consistent index of the actual sediment yield to the lake. The assumptions of continuity and synchroneity of lacustrine sediments is common in lake sediment-based literature. Since cores were taken from the deepest point of the lake the index will likely be an overestimate of actual yield because of sediment focusing effects in the lake basin. In lakes with a flat bottom and less sediment focusing, the sediment yield index will approach the actual yield. All lakes are large enough to be considered effective sediment traps, so trap efficiency of the study lakes is not included in any of the yield calculations. In order to make lake-to-lake comparisons of catchment denudation rates, the sediment yield index can be converted to a specific sediment yield, or sediment yield per unit of contributing basin area: Specific Sediment Yield = Sediment Yield / Drainage Basin Area = (Background Sedimentation Rate x Lake Area) / Drainage Basin Area The specific sediment yield should account for the areal focusing of sediment from the contributing land surface into the receiving lake. Units used for sedimentation rates and yields throughout this thesis are listed below. To clearly define what the area dimensions are intended to represent, italic characters are used for drainage basin area measurements (e.g. m2 and km2) and normal characters are used for lake surface area measurements. Lake sedimentation rate (calculated at the sediment coring site): g/m2/yr Sediment yield for the study lake: g/yr Specific sediment yield for the study catchment: g/m2/yr or Mg/fcm2/day 3.3.3 Varve Counting Some of the lakes had visible varving over a segment of their sediment cores. The deposition of annual laminations is often associated with poor oxygenation of bottom lake waters due to reduced or non-existent bottom water circulation. The oxygen-poor bottom waters contain high concentrations of ions derived from the sediments in the reducing environment at the sediment interface. These conditions are hostile to bottom-dwelling fauna. The absence of bioturbation results in undisturbed layering of the sedimentation load. Seasonal variations in the oxygen content of the bottom waters may result in a couplet of lamina that represents one year of deposition. A light half of the couplet may form from iron 23 oxides that precipitate as a result of partial oxygenation of the deep water during a turnover period. During other times of the year, when the oxygen level is very low, ferric oxides are reduced to the ferrous form and appear as black iron sulphides. Under such conditions, much of the organic matter may not completely decay and may further blacken the second half of the couplet. These anaerobic-reducing areas become populated with sulphur bacteria, forming black iron sulphides that also darken the sediments. Generally, each pair of black/grey laminations represents one year's accumulation of sediment, and therefore these couplets provide the basis for calculation of an absolute chronology. These results can be used to confirm the relative chronology established by the 210Pb dating procedures. The intervals over which continuous varving was present and a count of laminations was estimated in the field by visual examination of split sediment cores. It was observed that the laminations became more easily distinguishable if the core was allowed to partially dry before making the measurements. More accurate estimates of the varved core intervals (i.e. top and bottom core depths over which continuous varving is observed) and the number of laminations over that interval were made in the laboratory by magnifying the split core photographs taken in the field. The average sediment accumulation rate over that interval was calculated using the following formula: Sediment Accumulation Rate (g/m2/yr) = DBD x ADepth / # of varves Where: DBD is the average dry bulk density over the varved core segment ADepth is the length of the varved interval # of varves is the count of light/dark lamination couplets 3.3.4 Organic Content Organic content was measured using the standard loss on ignition technique (Hakanson and Jansson 1983). Weight loss of a dried sample is determined after being heated to 550°C for 4 hours in a furnace. Loss on ignition is expressed as the percent mass of the dried sediment sample, given by: % organic content = (Wd - Wr)/Wd Where: W d is the dried sediment sample weight Wr is the inorganic residual weight of the sample after the furnace burn Lake organic matter can be either autochthonous, especially in nutrient rich (i.e. eutrophic) lakes that promote excessive algal blooms, or allochthonous, where large amounts of organic debris is transported into the lake from inflowing streams. Usually, in studies of catchment erosion, the organic component of the sediments is subtracted out so that only the minerogenic component of the lake 24 sediment is considered. Due to the large number of sediment samples in this study, only selected lake sediment samples were measured for organic content. Lakes that had dramatic events or significant trends in their sediment accumulation rates were selected for this additional analysis so that further insights into the causal mechanisms could be gained. 3.3.5 Particle Size Analysis Particle size analysis was carried out on a small set of study lakes in order to estimate the probable range and trends in the caliber of sediment found in the study lakes. Dry sieving was used to separate the sand class (>63um) from dried sediment samples. Particle size distributions for the remaining sediments (<63um) were established using a Micromeritics SediGraph 5100 system. Dispersant was added to the samples to ensure the disaggregation of clays. Silt and clay divisions were determined from the SediGraph standard output. Smear slides were also prepared for a rough visual determination of the sediment composition (e.g. minerogenic grains, diatoms, and organic debris). 3.4 GIS Database Development 3.4.1 Acquisition of Primary Landscape and Land Use Information Critical to the project has been the application of GIS technology for the development, maintenance, and analysis of the lake catchment inventory database. This work has been completed primarily with ARC/INFO by Environmental Systems Research Institute (ESRI) on a network of SUN Microsystems SPARC workstations. Several key existing databases have been used as basic inputs into the GIS for landscape-level spatial analysis. The two most important sources of digital data include the provincial terrain resource information management maps (TRIM) and the Ministry of Forests (MoF) forest cover mapping (FC1). Brief descriptions of these databases are as follows: TRIM: Description: Terrain resource information management maps are available for the entire province. This data source is part of the BC Digital Atlas and is used as a baseline georeferencing framework. A number of spatial themes are provided, including: Coastlines, Hydrographic Structures, Water Bodies, Water Courses, Elevation Model, Contours, Land Cover, Buildings, Designated Areas, Toponymy, Roads and Railways, and Other Landmarks. Themes were compiled digitally primarily utilizing high level (1:60 000 and 1:70 000) vertical air photos, as well as satellite imagery, GPS and current, importable baseline data resident in other agencies. 25 Source: Geographic Data BC FC1: Description: A provincial forest inventory has been developed and maintained through re-inventory, update and growth and yield programs. The primary usage of the forest inventory data is for the planning and management of the timber, range and recreation resources. The resource database consists of Forest Inventory Planning attribute files (FIP) and digital graphic files (FC1). The FIP file contains description statistics including location, area, species composition, age, height, density and history, plus land-based management and resource overlay information. The FIP file is a geo-referenced, map-based file and can be used, in conjunction with its corresponding graphics (FC1) file. The FC1 file depicts forest inventory data for use in the preparation of inventory maps. Source: British Columbia Forest Service- Resources Inventory Branch Several other basic inputs were also incorporated into the GIS database. These include the following secondary information sources: • GPS positioning and notes taken from field sampling locations • Aerial photography (Provincial and Federal vertical photography - available at a variety of scales and dates, and oblique aerial photography taken from the field) • Lake inventory reports ("Fisheries Warehouse" - Lake Survey and Lake Classification Project reports by the Ministry of Environment, Lands, and Parks (MELP) Fisheries Branch, and other published content analyses) • Forest Development Plan maps (1:5000 paper maps available for some lakes) • Historical mapping (e.g. road maps, recreation maps, etc) • Personal communication updates from MELP and MoF personnel 3.4.2 Lake Catchment Base Map Construction The Feature Manipulation Engine BC (FMEBC) was used to convert the TRIM and FC1 files into ARC/INFO coverages. With all the data in a common format and projection, base maps for the lake 26 catchments were constructed. The first step was to delineate the watershed boundary for the catchments. This was done by 'heads up' digitizing of the basin boundary by displaying the water features, contour lines and break lines on the workstation display, and then digitizing the lake watershed on screen. Starting at the lake outlet the lake basin divide was digitized by following ridge break lines around the contributing hydrological network of the lake. The sediment core sampling locations within each lake were also digitized from maps and notes used during field season. The TRIM and FC1 coverages for each lake were clipped using the newly created basin cover to leave only the features that are within the lake catchment. The TRIM data was also reclassified using TRIM attribute codes into the following themes required for the project: Lakes, Rivers, Wetlands, and Roads. Themes that contained zero features after reclassification were removed from the lake workspace. Some work was required to 'clean-up' the data (creating polygon topology, closing polygons, adding polygon labels, etc.). Each lake subdirectory now contained the basic topographic themes that constitute the base map of the lake catchment. The following list defines these themes: Table 3.1: Lake Catchment Base Map Layers Name Type Description Basin Polygon Delineates the watershed boundary for the lake catchment Core Point Shows the location where cores were sampled from the lake Lakes Polygon Contains all lakes and ponds within the lake catchment Rivers Line Contains all rivers within the lake catchment Wetland Polygon Contains all swamps and marshes within the lake catchment Roads Line Contains the road network within the lake catchment Forest Line/annotation Shows all the forest cover polygon boundaries with annotation 3.4.3 Digital Elevation and Hydrologic Model Development This study requires extensive use of Digital Elevation Models (DEMs) and other raster layers derived from the D E M to develop landscape variables based on catchment morphometries and hydrology. A D E M was created using the TOPOGRID ARC/INFO command. The TOPOGRTD command is an interpolation method specifically designed for the creation of hydrologically correct DEMs from 27 comparatively small but well selected elevation and water feature coverages. It is based upon the ANUDEM program developed by Hutchinson (1988, 1989). A brief summary of ANUDEM and some applications is given by Hutchinson (1993). Inputs required for TOPOGRID include the TRIM spot elevations and break lines, the rivers line coverage, the lakes polygon coverage, and the basin boundary line coverage. After the DEM was developed slope and flow direction maps were derived using built-in ARC/INFO commands. These coverage themes are needed to estimate the paths and transport capacity of water and sediment through the lake watershed, and therefore have important hydrological and geomorphological significance. All grids were checked with topographic maps and aerial photographs of the lake catchments to confirm accurate representation of the watershed. 3.4.4 Refinement of Historical Land Use Information Roads and cutblocks are the primary land use history data used in this project. The starting points for developing these layers were the TRIM and FC1 databases. Attributes were added to these layers to store the year of the disturbance and a range of years if the year of disturbance could not be absolutely determined. The FC1 annotation contained dates for many of the cutblock polygons. Initial plots were produced of the base map layers and preliminary land use layers for verification and updates. Aerial photography was used to confirm the layout of the history layers and determine the approximate timing of the disturbance features. Aerial photography available for the study region includes federal photography at medium scales (1:30 000 to 1:40 000) taken in the 1940's, provincial photography at a variety of scales (1:15 000 to 1:70 000) taken on many dates ranging from the late 1940's to current, and oblique low level photography taken during the field sampling season. The most recently available photography was used to check the correctness of the history layers. The TRIM and FC1 data was found to be incomplete and inaccurate for many of the study lake catchments. Errors and omissions were corrected and updated by hand on the draft plots. In a few cases, where the land use history was more complex, the photos were copied or traced for digitizing on return to the GIS laboratory. After the confirmation and correction of the history layers, all features were dated using earliest available photography. Due to the high value of natural resources within the study area, extensive air photo coverage was available for most lakes. This permitted dating of land use changes to within approximately five year intervals, which is well within the temporal resolution of the 210Pb dating technique used to estimate sediment accumulation rates. Any other significant land use features or geomorphic activities observed in the aerial photographs were also recorded for each lake. 28 Secondary draft plots were then produced for further verification of the GIS database by MELP and MOF staff at the forest district offices. This final verification corrected any remaining errors and omissions in the GIS data, and completed the construction of the lake inventory database. 3.4.5 Extraction of Landscape and Land Use Variables Two types of variables were extracted from the GIS database. The first set of variables are landscape indices, which are considered static over the time scale of this study. These indices consist of lake catchment morphometric parameters that relate to the sediment production, conveyance, and storage for the basin. The second set of variables are dynamic (time dependant) land use indices. These indices consist of planimetric parameters of land use change within the lake catchment which relate to potential anthropogenic modification in the basins sediment transfer. The land use indices are calculated on a yearly basis since the time of the first land use disturbance. Customized macro programs were developed to automate the extraction of all indices. Basic length and area measurements are in km and km2, elevations are in meters, and slopes are in degrees. All of the landscape and land use indices extracted from the GIS database are listed below: Landscape Indices: 1) Drainage Basin Area - Total land area of the lake catchment 2) Study Lake Area - Area of the inventoried lake 3) Lake Area - Total surface area of all lakes upstream of the inventoried lake 4) Wetland Area - Total surface area of wetlands (swamps and marsh land) within the lake catchment 5) Valley Flat Area - Total area of valley flats (slope less than 1 degree) within the lake catchment 6) Stream Length - Total length of streams within the lake catchment (specific slope classes can be selected and drainage densities can be calculated using drainage basin area) 7) Elevation Statistics - Maximum, minimum, mean, and standard deviation of DEM values for the lake catchment 8) Slope Statistics - Mean and standard deviation of slope values calculated from the DEM for the lake catchment 29 Land Use Indices: 1) Percentage of Basin Logged - Percentage of total land area of the lake catchment that has been logged (can include slope and distance modifiers, eg. percentage of basin logged within 100 meters of the lake or streams on slopes greater than 30 degrees) 2) Road Density - Density of roads within the lake catchment (can include slope and distance modifiers as described above), in units of km/km2 3) Percentage of Streams Logged - Percentage of streams that lie within logged areas within the lake catchment 4) Number of Stream Crossings - Number of locations a road crosses a stream within the lake catchment 5) Shape Index of Cut Areas - Index describing the shape of cut areas (= 1 for a circle and increases for more complex shapes) calculated from cumulative cutblock areas and perimeters: Shplnd = perimeter/2*sqrt(7t*area) 3.4.6 Data Transformation Analysis of the landscape data consisted of regression with tests of statistical significance, which are based on the assumption that variables are normally distributed. Variables describing natural landscape characteristics are often log-normally distributed. As can be seen in Figure 3.1, log transformed data better approximate the normal distribution. Although the log transformed data do not perfectly fit the normal distribution, most statistical tests are quite robust with respect to deviations from the normal distribution (Trainor and Church 1996). Based on visual examination of variable histograms, the log transformation was deemed necessary for all landscape indices except for lake elevation and drainage density. 30 Figure 3.1: Log Transformation of Slope Data Histogram of Raw Slope Data: -10 -5 0 5 10 15 20 25 30 35 Slope (degrees) Histogram of Log Transformed Slope Data: log(Slope) Normal distribution with the same mean and variance is superimposed on histograms 31 4 THE STUDY LAKES AND THEIR SEDIMENT RECORDS 4.1 Introduction The results from the GIS and laboratory work are presented and discussed in this chapter. The lake set has been stratified by the physiography of the contributing catchment area for each lake. The pysiographic regions are based on observations made in the field and the geological and geomorphological work done in the study area by Clague (1984). The following regions have been selected and delineated: North Coast, Hazelton Mountains, Skeena Mountains, Nass Basin and Major Valleys, and Nechako Plateau (see Figure 4.1). Sampling density varies between the regions and the distribution of sampled lakes is inhomogeneous within each region. This is a consequence of lake accessibility limitations and, to lesser extent, the geographical occurrences of lakes in the study area. The study lakes in each region are listed in Table 4.1. This stratification was used because dominant processes of sediment transfer are likely variable between regions in response to differences in topography, geology, and climate. The discussion of the study lakes and their sediment records is organized into these five physiographic study regions, each consisting of three sections. The first section describes the landscape (based on field observations and work by Clague (1984)) and climate (primarily interpolated from the National Atlas of Canada, 5th edition) of the physiographic region. The second section describes the study lakes and their contributing catchment areas. Landscape and land use data extracted from the GIS database is presented in this section. The third section for each study region presents the sedimentary records for the sampled lakes. The primary focus is on the sediment accumulation rate profiles derived from 210Pb dating of the sediment cores. Varved sediment samples, organic content of sediment, and particle size work is also presented for lakes that were selected for additional laboratory analysis. Some interpretations of the sediment signatures are included for each study region. Lakes that are representative in the data set or that make interesting case studies (e.g. special landscape or land use characteristics, unique patterns or trends in the sediment records, or greater quality or quantity of available lake sedimentary data) are identified and discussed in greater detail. An analysis and discussion of lacustrine sedimentation patterns over the entire study region is included in chapter 5. 4.2 North Coast Region 4.2.1 Description of Study Area The North Coast Region is situated on the northwest coast of British Columbia. It borders on the Pacific Ocean, stretching from Douglas Channel in the south to the Portland Canal in the north. 32 33 Table 4.1: Study Lake Classification North Coast Amoth Dragon Jade Khtada Kwinamuck Minerva Toon Tyke William Hazelton Mountains Aldrich2 Chisholm Collins Dennis2 Douse Gordeau1 Jackmould Louise Mcbride Mcdonell1'2 Newcombe Sandstone Shea Wjholland Skeena Mountains Alpha Beta Camp Damsumlo1 Farewell Lake211 Loneisland Smokee Twin Unnamedl Nass Basin and Major Valleys Arbour Arrowhead Bigfish Derrick Duckwing Elizabeth Flatfish Hoodoo Kwinageese W. Lakel3 Lake4 Mitten Niskaeast Octopus Paw Pentz Sandal Unnamed KM1 Nechako Plateau Binta1 Bittern Boomerang2 Boucher Bristol Clota Doris2 Haney Horseshoe Lake10 Lake31 Lake8 Lakez Ligitiyuz Parrot Pinetree2 Takysie Tanglechain1'2 Torkelsen Lake names in italics have had no land use activities in catchment 'Double basin lake Component of a cascading lake system 34 Spectacular coastlines, steep-walled fjords, and rugged mountains characterize the region. Elevation ranges from sea level to glaciated peaks of over 2000 meters. Relief is very steep throughout most of this region. The landscape ranges from low floodplains covered with cottonwood forests along the Nass and Skeena rivers, through forests of western hemlock, western redcedar and sitka spruce, to alpine tundra and glaciers at higher elevations. Dominant biogeoclimatic zones in the region include coastal western hemlock, mountain hemlock, and alpine tundra. The North Coast study area contains portions of the North Coast and Kalum forest districts. Currently, less than 10% of the timber supply areas is considered profitable for timber extraction because of higher-than-average production costs associated with the remote and rugged terrain. The North Coast Mountains consist of Cretaceous and Tertiary granitic intrusions (Clague 1984). Major rock outcrop areas show fresh glacial landforms such as cirques, aretes and horns. Where bedrock is not exposed it is commonly thinly mantled by soil. Near-surface rock is the most common terrain type in the region. The most abundant granitic rocks are quartz diorite and granodiorite. Mean annual precipitation exceeds 2500mm and in some area surpasses 3500mm. Maximum precipitation is recorded during the winter months. Air temperatures are strongly influenced by topography. Winter temperatures decrease with increasing elevation and distance inland. The mean January temperature of Prince Rupert on the coast is about 1.8°C, and at higher elevations inland it is below -10°C. Mean July temperatures in the main valleys are about 14-17°C, several degrees higher than on mountain tops. 4.2.2 Description of Study Lakes Nine study lakes were selected from the North Coast region. The North Coast region and the location of the study lakes were shown in Figure 4.1. Maps of the lake catchments are included in Appendix F. The North Coast lakes were formed by glacial erosion in the mountains bordering the main valleys. They are medium to large sized lakes with an elongated shape and very steep-sided bathymetry and immediate shoreline. They are deep lakes scoured into bedrock along faults and associated structural weaknesses. Extensive rock outcrops are major features in the upland areas. Most of the terrain is covered in a thin veneer of till and colluvium, with a few deeper pockets of till and alluvium. Mass wasting is a dominant process on the steep valley sides. Avalanche tracks, talus slopes and alluvial/colluvial fans directly enter the study lakes. The soils are thin Lithosols with some Ferro-Humic Podsols. These soils support sparse forests of Engelmann spruce, alpine fir, and mountain hemlock. Mixed marsh, swamp, and thicker forested areas cover portions of the alluvial fans adjacent to the lakes. 35 Higher elevation areas are encased in ice and permanent snowfields. Landscape indices for the North Coast lakes are tabulated in Appendix B. Amoth, Jade, Khtada and Toon lakes have had no land use disturbance. The other five lakes have all had some degree of road construction and timber harvesting within the lake catchment. Dragon Lake has had the longest land use disturbance history beginning with road construction in the late 1950's. Over the following four decades, 33% of the basin was harvested and a major access road was developed near the lake. The timber removal around Tyke was done by helicopter logging which was active during the sediment core sampling of the lake. About 30% of the shoreline had been logged before sampling. All of the other disturbed lakes contained only minor logging and road development. A summary of land use disturbance for the North Coast lakes is included in Appendix C. 4.2.3 Lake Sediment Records Sedimentation rate profiles for the North Coast study lakes are included in Appendix D. Background mid-lake sedimentation rates range from 49 g/m2/yr in William Lake to 2050 g/m2/yr in Amoth Lake. The exceptionally high background rate in Amoth Lake reflects the large contributing drainage area, steep surrounding terrain, and close proximity to the Pacific Coast. Background sediment yield is strongly related to the contributing drainage area in this region (Figure 4.2). Yield is approximately proportional to drainage basin area to the power 1.38, implying a considerable non-linear increase of sediment yield downstream. The sample size of North Coast lakes is too small to attempt any multivariate analysis on the influence of landscape variables on background sedimentation rates. Varves were present in four of the North Coast lake cores (Toon: 0-25cm, Amoth: 14-30cm, Jade: 8-9cm, and Dragon: 5-10cm). The Toon Lake core was the only sample that was continuously varved over the entire length of core. By using the annual laminations to date sediment, an absolute chronology can be established for the sediment deposits. This provides an opportunity to confirm the relative chronology established by 210Pb dating. Sediment accumulation rates calculated using each dating method for Toon Lake are compared in Figure 4.3. Suspicious outlier points and estimated background sedimentation rates have been marked in the plots. The top 19cm of the core sample was estimated by varve counting to be 103 years of sediment accumulation. This represents a lower limit since there were a couple short sections of the core where the varving was too faint to count. 210Pb dating of sediments at that depth estimated the deposition date to be 113 years before present. Average sedimentation rates over the core length were 418 and 412 g/m/yr as calculated by 210Pb dating and varve counting respectively. The sedimentation rate profile derived from varve counting shows a background rate of about 270 g/m2/yr with peaks of approximately 450 g/m2/yr in the late 1920's-early 1930's and 1150 g/m2/yr in the late Figure 4.2: Sediment Yield as a Function of Drainage Basin Area, North Coast Lakes 10000 s c tu E •5 tu w 1000 £ 100 10 y = 5.76x'J0 R2 = 0.86 Dotted line is 95% confidence interval for fit 10 100 Drainage Basin Area (km2) 1000 210 Figure 4.3: Pb vs Varve Counting Sedimentation Rates for Toon Lake 1200 210Pb Dating u >> 1000 "5k ca e o 800 600 5 400 e cu .§ 200 cu - - - background sedimentation rate outlier point loss of sediment 1880 1900 1920 1940 Year I960 1980 2000 1200 1000 OS T 3 cu 800 600 2 400 tu S 200 Varve Counting background sedimentation rate outlier point vatues 2000 37 1970's-early 1980's. The Pb profile shows a background rate of about 350 g/m2/yr with peaks of approximately 550 g/m2/yr in the late 1920's-early 1940's and 700 g/m2/yr in the early 1980's. Both methods gave very similar averaged sedimentation rates and show similar temporal patterns of accumulation. There are some moderate differences, however, between estimated rates of sedimentation for background and peak values. Amoth, Jade, and Dragon Lakes had varving over a segment of their sediment column. In Amoth Lake from 14 to 30 cm of sediment depth the average sedimentation rate calculated by varve counting was 2533 g/m2/yr, slightly less than the 210Pb averaged estimate over that range of 2723 g/m2/yr. In Jade Lake, between 8 and 9cm of depth, sedimentation rates by varve counting and 210Pb dating were very close at 1050 and 1075 respectively. In Dragon Lake, from 5 to 10cm of depth, the average rate estimated by varve counting was 76 g/m2/yr, slightly greater than the 210Pb estimate of 52 g/m2/yr. These results show that the 210Pb dating technique does appear to provide reasonable approximations of sediment accumulation rates. Sedimentation rates in the North Coast lakes are highly variable over time. This reflects the episodic nature of sediment transfer in mountainous watersheds of British Columbia. The highest amount of variability is observed in lake catchments with an average slope greater than 30°. This includes Amoth, Khtada, Toon, and Tyke Lakes (profiles shown in Figure 4.4). Khtada shows peak sedimentation rates 300% higher than the estimated background rate. The other three lakes have a greater number of distinguishable peaks of lesser magnitude. The actual peak rates cannot be determined since the magnitudes are averaged measures of sedimentation over many years. The sediment cores from Jade and Toon lakes were further analyzed for organic content. Jade Lake is the only lake that shows a decreasing trend in sedimentation rates over the entire analyzed length of core. Organic content measurements for Jade were 7.3% (0 - 0.5cm), 5.8% (8 - 9cm), and 5.3% (16 -18cm). The small change in organic content over the length of this core cannot explain the unique decreasing sedimentation trend observed. Organic content was measured for the entire length of the Toon Lake core. Organic content was highly variable, with an average content of about 21.7%. The higher organic content in Toon Lake is likely a result of higher lake productivity in this lower elevation lake (235m vs 816m for Jade Lake). There appears to be an inverse relation between sedimentation rate and organic content for this lake, which suggests that catchment-derived clastic inputs primarily control sedimentation in Toon Lake (Figure 4.5). 38 Figure 4.4: Natural Disturbances in Lake Sedimentation, North Coast Lakes 100 90 80 70 60 50 -\ 40 30 20 10 Amoth 1860 1880 1900 1920 1 940 year Khtada ! 250 -\ 100 50 1920 1940 year J 1980 2000 100 90 80 70 60 50 40 30 20 10 H Toon 100 90 80 70 60 50 40 30 20 10 Tyke 1860 1880 1900 1920 1940 1960 1980 2000 year A 1860 1880 1900 1920 1940 1960 1980 2000 year Note: Horizontal scales are not all equivalent Figure 4.5: Toon Lake Sedimentation Rates and Organic Content evT~ E CD CD c o c5 -t—* c o E T3 CD W 800 700 600 500 400 300 200 100 1880 Total sediment load (clastic + organic) Clastic component of sediment load 1900 1920 1940 year 1960 1980 2000 39 Particle size distribution was also analyzed for sediments from Toon Lake. The sediment is primarily composed of medium silt to fine sand (8|lm - 125um). A smear slide sample showed that the sediment was mainly clastic. A large amount of quartz mineral grains were observed in the sample. The greatest amount of timber harvest has occurred in the Dragon Lake catchment. Land use began with road construction in 1958, and has continued periodically until today. Over the last 40 years 33% of the catchment has been harvested and the road network has been developed to a density of 0.9 km/km2. The sedimentation rates in Dragon Lake have been increasing steadily since the time of initial land use disturbance, up to 67% above background levels in the late 1990's. Land use activities cannot be isolated as the cause for this trend because a similar increase in sedimentation is observed in nearby Kwinamuck Lake. In Kwinamuck Lake sedimentation rates have also been increasing steadily since the 1950's, up to 79% above background in the late 1990's. This increasing trend began about 30 years before any land use disturbances in the catchment. Land use in Kwinamuck Lake, which consisted of 12% of the area harvested and road development to 0.6 km/km2 from 1986 to 1997, did not appear to have any influence on the naturally increasing sedimentation rates. The helicopter logging around Tyke Lake in the early 1990's had no noticeable effect on sedimentation rates. A sharp increase from 51 to 102 g/m2/yr of sediment accumulation is recorded in the William Lake sediment record following timber removal and significant road development on the north shore of the lake. A higher rate, however, of 111 g/m2/yr was reached in 1898 in the absence of any land use activity. In Minerva Lake sedimentation rates have been increasing since steep slopes were logged on the eastern shore of the lake. The rates of sedimentation, however, remain well below those observed earlier in the record. Plots showing sedimentation rates and land use disturbance patterns for all lakes are included in Appendix D. 4.3 Hazelton Mountains Region 4.3.1 Description of Study Area The Hazelton Mountain range runs north-south, parallel to the Coast Mountains. The region is bounded by the Kitsumkalum-Kitimat Trough to the west, the Nass Basin to the north, the Kispiox and Bulkley Rivers to the east, and the Interior Plateau to the south. Elevation ranges from close to sea level in the major valleys to glaciated mountain peaks over 2000m in height. There are five biogeoclimatic zones in the Hazelton Mountains study area. At lower elevations western hemlock forests dominate, changing to mountain hemlock, Engelmann spruce-subalpine fir, and alpine tundra and glaciers at higher elevations. To the southeast, where the Hazelton Mountains converge into the Interior Plateau, sub-boreal spruce forests begin to dominate the landscape. The region contains the eastern half of the Kalum forest district and western portions of the Kispiox, Bulkley and Morice forest districts. 40 The Hazelton Mountains study region lies within the Intermontane Belt. Within the study area, this belt is dominated by sedimentary and volcanic rocks of Jurassic-Cretaceous age. Bedrock intrusions are not as widespread and relief is more moderate than that observed in the Coast Mountains. Precipitation is strongly controlled by orographic effects in this region. Mean annual precipitation ranges from over 3000mm on the windward side of the mountains to about 500mm on the leaward side. Maximum precipitation is recorded during the winter months. Mean daily temperatures range from about 14°C in July to about -10°C in January. 4.3.2 Description of Study Lakes Fourteen study lakes were selected from the Hazelton Mountains region. The Hazelton Mountains region and the location of the study lakes were shown in Figure 4.1. Maps of the lake catchments are included in Appendix F. Pleistocene sediments impound all lakes in this region, although bedrock and active delta areas along the shorelines are not uncommon. Lake sizes and shapes are highly variable. Immediate shorelines are vegetated by stunted conifers, alder, and willow. Wetland areas are common in close proximity to the study lakes. The surrounding country consists of spruce and fir forests on rolling to steep terrain. Some lake catchments also contain high mountain areas that remain snow covered for most of the year. Two core sampling sites were required for Gordeau and McDonell Lakes because they contained distinct double basins. Aldrich, Dennis and McDonell lakes comprise a cascading lake system. Landscape indices for the Hazelton Mountains lakes are included in Appendix B. Douse and Shea Lakes have had no land use disturbance surrounding the lakes. All of the other lakes have had some road construction and timber harvesting within the lake catchment. Land use disturbances range from West Julian Holland Lake with a road density of 0.01 km/km2 and 2% of its drainage basin harvested, to Collins Lake with a road density of 1.45 km/km2 and 42% of its drainage basin harvested. The earliest logging activity occurred around Collins and McBride Lakes in the late 1950's and early 1960's. This early logging activity commonly involved harvesting and yarding trees directly along stream channels. Mining occurred in the Aldrich Lake catchment from the early 1920's until 1954, with the greatest amount of production occurring in the later years of the mine's operation. Smaller scale mining also took place in the Louise Lake catchment through the 1970's and 1980's. In approximately 1940, 21% of Sandstone Lake's catchment was burned in a natural forest fire. A summary of land use disturbance for the Hazelton Mountain lakes is included in Appendix C. 41 4.3.3 Lake Sediment Records Sedimentation rate profiles for the Hazelton Mountain study lakes are included in Appendix D. Background mid-lake sedimentation rates range from 40 g/m2/yr in West Julian Holland Lake to 480 g/m2/yr in Basin B of McDonell Lake. Like in the North Coast region, the contributing area largely controls the background sedimentation rates. Storage potential, defined by the amount of storage zones -lakes, ponds, wetlands, and floodplains - upstream from the lake, also appear to influence the sedimentation rates in this region. Stepwise linear regression was performed using all the landscape indices as the independent variables with the estimated background sediment yield to the lake as the dependent variable. Drainage basin area and total valley flat area, which includes upstream water bodies, were the most significant predictor variables. The regression equation is of the form: log(background sediment yield) = 0.16 + 1.451og(drainage area) - 0.691og(valley flat area) R2 = 0.83 None of the lakes had any visible varving. Aldrich, Newcombe, Douse, and Shea lake sediments were analyzed for organic content. Average organic content results were 12%, 24%, 23%, and 11% for the lakes respectively. No significant temporal trends were present, except in Newcombe Lake, where organic content was about 5-6% higher in the last few decades than in the beginning of the 1900's. The most significant peaks in sedimentation rates occur early in the records of the two control lakes for the region: Douse and Shea. There was no significant change in organic content coinciding with these peaks. The cause of these large fluctuations in sedimentation rates is, unfortunately, unknown. Possible causes include sediment-flushing events from the catchment, post depositional disturbances within the lake basin, or errors in the 210Pb dating. The remainder of the sedimentation rate profiles for both lakes are relatively steady near background levels. Included in the lake set for the Hazelton Mountain region is a double basin lake and a three lake cascading system that also includes a double basin lake. It is useful to look at these lake systems to address trap efficiency of the lakes and cumulative watershed effects. Situated in the southernmost area of the Hazelton Mountains is Gordeau Lake (Figure 4.6). This lake contains two distinct lake basins of similar size and depth. Background sedimentation rate at the two coring sites and the estimated specific yield for each basin are included in Figure 4.6. Basin A has a lower sedimentation rate and specific yield than Basin B. Most of the inflow tributaries enter Basin B of Gordeau Lake. A large portion of the sediment yield from those tributaries is trapped in that basin of the lake. Although the main inflow to the lake enters Basin A, it drains a large lake upstream that likely traps a large portion of the catchment's total sediment production. 43 Aldrich, Dennis, and McDonell Lakes comprise a lake cascade system located about 12km west of Smithers. McDonell Lake is the other double basin lake in the Hazelton Mountain region. Figure 4.7 shows the lake cascade catchments and the extent of land use around the lakes. Specific sediment yield decreases downstream, as more sediment goes into storage while moving through the lake cascade. Specific yield increased slightly in Basin A of McDonell Lake, possibly due to focusing effects and higher sediment supply from steep adjacent slopes. Figure 4.8 shows the sedimentation rate profiles for each of the lakes. Road and mine development began north of Aldrich Lake in the early 1920's. Production was intermittent between 1930 and 1940, but by 1950 the mine operated at its highest production rates. The final year of operation was 1954. Mid lake sedimentation rates in Aldrich Lake increased steadily from a background rate of about 300 g/m2/yr to close to 700 g/m2/yr during mine operation. Sedimentation rates reached their highest levels of 779 g/m2/yr in the decade following mine production. This peak in sedimentation was likely associated with road failures and a blowout that occurred in the old tailings dump. Sedimentation rates dropped in the following years, but then again started to increase when forestry activities began in 1984. The mining impacts observed in Aldrich Lake did not propagate downstream to Dennis Lake. Dennis had a consistent background rate of about 370 g/m2/yr for most of its sediment record. However, rates increased to about 600 g/m2/yr following road construction and timber harvest beginning in 1983. Basin B of McDonell Lake had a large increase in sedimentation rates following significant road construction in the 1950's. Rates increased sharply from a background of less than 500 g/m2/yr to a high of 2700 g/m2/yr. Rates recovered to under 1400 g/m2/yr over the following decades, but are increasing again late in the record with recent road construction and timber harvest. The sediment record of McDonell Lake Basin A did not show the dramatic increase in sedimentation observed in Basin B following early road construction, although there is a small peak in the sediment profile that coincides with road construction and timber harvest in the 1980's. Overall, there is no evidence of cumulative effects in this cascading system - lakes appear to be significant sediment traps and act as buffers in the connected lake system. Both Collins and McBride Lakes have had slowly increasing sedimentation rates for their entire lengths of record. The heavy land use disturbances in those lakes did not seem to influence the lake sediment signatures in any significant way. This is surprising since Collins and McBride were the most heavily disturbed lake catchments in terms of logging in the Hazelton study region. West Julian Holland Lake, which was only slightly disturbed, also showed no noticeable land use impact in the sediment record. The other six disturbed lakes all showed a significant increase in sedimentation that coincides closely with road construction and timber harvest in the basin. Sedimentation rate profiles for these lakes Figure 4.7: Aldrich - Dennis - McDonell Lake Cascade 44 / \ / Roads ~l Divide n Core location SCuts Rivers J Lakes Wetland 1 0 1 2 3 Kilometers Specific Sediment Yield: Aldrich - 0.026 Mg/km 2/day (moving down cascade) Dennis - 0.0098 Mg/km 2/day McDonell Basin B - 0.0055 Mg/km 2/day McDonell Basin A - 0.0066 Mg/km 2/day 45 Figure 4.8: Sediment Accumulation Rates (SAR) and Land Use for Aldrich, Dennis, and McDonell .00 -, SAR(g/rrrVyr) ALDRICH M ining ^ 1867 1887 1D07 1937 1947 19G7 R o a d Densi ty # of Stream C r o s 0,03 -o.o; - % L o g g e d Zymoetz River SAR(g/rrf/yr) MCDONELL BASIN A JI R o a d Densi ty # of Stream C r o s s i n g s IL 0.D1E 0.01 O.OOS % L o g g e d Zymoetz River SAR(g/mfVyr) DENNIS 1975 19! R o a d Densi ty # o f S t ream C r o s s i n g s % L o g g e d Connected Basins SARfg/nWyr) MCDONELL BASIN B 1S21 1931 1941 1*51 l l l l 1971 19S1 R o a d Density # of Stream C r o s s i n g s Note: Graph axes are at different scales 46 are shown in Figure 4.9, wherein the time period following land use disturbance has been shaded. The land use impacts are summarized in Table 4.2. In some lakes, sedimentation rates were rising before the onset of forestry. In all lakes, except for Chisholm, the post disturbance sedimentation rates are significantly higher than those rates observed earlier in the record. Chisholm Lake had a natural disturbance in the sediment record that was comparable to the increase following land use in the basin. Increases in sedimentation following timber harvest and road construction ranged from 50% to 130% higher than the estimated background rates. Although considerable impacts were observed in the cascading lake system (Aldrich -> Dennis -> McDonell), these lakes are not included here because their land use histories and sedimentation responses are more complex. There is no obvious pattern between the degree of disturbance and the magnitude of the sedimentation increase. The fire in the catchment of Sandstone Lake had no noticeable effect on sedimentation rates. Table 4.2: Land Use Impacts of Selected Hazelton Mountain Lakes Lake Name % Logged Road Density* Stream Crossings % Increase in Sedimentation Notes Newcombe 8% 0.4 51 133% Large number of small cuts, very high number of stream crossings Gordeau A 3% 0.4 5 111% Road crossing over major inflow upstream of lake Sandstone 6% 0.3 2 73% Minor disturbance, low energy system (high storage potential) Louise 18% 0.7 18 70% Limited mining activity also in catchment Chisholm 9% 0.7 13 57% Moderate disturbance, high energy system (low storage potential) Gordeau B 10% 0.8 2 55% Major road through basin, some logging immediately adjacent to lakeshore Jackmould 33% 1.9 14 50% Large portion of basin cut with high road density *Road densities are in km/km2 Figure 4.9: Sediment Accumulation Rates (SAR) of Selected Hazelton Mountain Lakes I SAR(g/rrf/yr) SAR(g/rrr7yr) GORDEAU BASIN B 1816 1836 1856 1876 1S96 1916 1930 1956 1976 1996 SAR(g/mVyr) LOUISE 1887 1807 1827 1847 SAR(g/rrf/yr) SANDSTONE J L SAR(g/nf/yr) GORDEAU BASIN A 832 1852 1872 1882 1912 1932 1952 1972 1992 SAR(g/mVyr) JACKMOULD 1848 1B68 18SS 1928 194S 19E SAR(g/rrrVyr) NEW COMBE 1113 1113 1171 1191 1913 1913 19S1 1973 1193 1877 1897 1917 1937 1957 1977 1997 Note: Shaded area shows time period following initiation of land use activities Graph axes are at different scales 48 4.4 Skeena Mountains Region 4.4.1 Description of Study Area The Skeena Mountains are the third major mountain range that runs north-south parallel to the Pacific Coast. They are bounded between the Skeena and Bulkley Rivers to the west and the Interior Plateau to the east. Elevation ranges from a few hundred meters in the valley bottoms to glaciated mountain peaks over 2000m in height. There are three biogeoclimatic zones in the Skeena Mountains study area. Most of the area is dominated by sub-boreal spruce, with some Engelmann spruce-subalpine fir, and alpine tundra and glacial regions at higher elevations. The region contains western portions of the Kispiox and Bulkley forest districts. Bedrock, surficial materials and general relief of the Skeena Mountains are similar to those of the Hazelton Mountains. The climate is more strongly influenced by cooler and drier continental air masses. Mean annual precipitation is only about 500mm, much less than that received in the coastal maritime regions. The distribution of rainfall is relatively uniform through the year. 4.4.2 Description of Study Lakes Ten study lakes were selected from the Skeena Mountains region. The Skeena Mountains region and the location of the study lakes were shown in Figure 4.1. Maps of the lake catchments are included in Appendix F. Lakes in this region tend to be small and irregular in shape. The surrounding terrain is similar to that found in the Hazelton Mountain lake catchments. The study lakes in the Skeena Mountains are the highest elevation lakes in the study, with elevations well over 1000m for most lakes. Grassy meadows and marsh areas are common. Some lake catchments also contain high alpine areas that remain snow covered for most of the year. Two sampling sites were required for Damsumlo Lake and Lake 21 because they contained distinct double basins. Landscape indices for the Skeena Mountain lakes are tabulated in Appendix B. Only Camp and Twin Lake have had any land use disturbances within their lake catchments. A summary of land use disturbance for the Skeena Mountain lakes is included in Appendix C. 4.4.3 Lake Sediment Records Sedimentation rate profiles for the Skeena Mountain study lakes are included in Appendix D. Background mid-lake sedimentation rates range from 40 g/m2/yr in Smokee Lake to 670 g/m2/yr in Twin Lake. Like in both the North Coast and Hazelton Mountains catchments, the contributing area largely 49 controls the background sedimentation rates. Drainage basin area and drainage density are the most significant predictor variables, as indicated by stepwise linear regression. The regression equation is of the form: log(background sediment yield) = 0.49 +0.801og(drainage area) + 0.27(drainage density) R2 = 0.84 Alpha Lake was the only lake in the Skeena Mountains that had visible varving in the sediment cores. Varves from 5 to 10cm of depth in the core indicated an average sedimentation rate of approximately 76 g/m2/yr. This is 27% higher that the average estimated 210Pb sedimentation rate of 60 g/m2/yr over the same core segment. The sediment signatures of five of the ten lakes in this region show significant natural disturbances in the past 100 to 150 years. Increases in sedimentation rates associated with these disturbances range from 75% to 650% above background levels. The 650% increase occurred in Basin A of Damsumlo Lake in the early to mid 1900's (Figure 4.10). Confirming that major disturbance is a peak sedimentation rate of 500% above background occurring at the same time in the other basin of the lake (also shown in Figure 4.10). The cause of this disturbance is unknown. The disturbances in Twin and Camp Lakes were also significant with peak sedimentation rates 130% and 370% above background, respectively. Episodic disturbances appear to be important processes of sediment transfer in the Skeena Mountains. Six of the ten lakes in this region show a consistent increasing trend in mid lake sedimentation rates beginning around 1950. The most extreme examples of this trend are observed in Beta and Farewell lakes (Figure 4.11). Over the last 50 years sedimentation rates have increased 152% and 167% in those lakes, respectively. Both of the sediment cores from these lakes were analyzed for organic content. Average amounts of organic content were 43% for Farewell Lake and 50% for Beta Lake. While there was no trend in organic content in Farewell Lake, organic content in Beta Lake increased by about 10% over the last 150 years. This suggests that the recent increase in sedimentation rates in Beta Lake may be partially related to increased lake productivity. Sediment samples from the lower and top sections of the cores were dry sieved to determine the proportion of sediment above the sand-silt class break (63um). The sand fraction of the sediments from Beta and Farewell lakes has increased from 46% to 54% and 47% to 54% respectively. This indicates that the transport capacity may have been increasing in these lake catchments over the sediment record. This trend of increasing sedimentation rates with higher sand content may be related to climatic change in the region. This will be investigated in the next chapter. Figure 4.10: Sediment Accumulation Rates (SAR) for Damsumlo Lake SAR(g/mfVyr) DAMSUMLO BASIN A Dsturbance 2000 1S0O . 1 I n 5 Background SAR(g/rrfVyr) DAMSUMLO BASIN B Dsturbance Background 1910 1930 1950 1970 1990 1920 193S 19SS 1969 197S 19S9 Figure 4.11: Sediment Accumulation Rates (SAR) for Beta and Farewell Lakes , SAR(g/rrf/yr) FAREWELL Note: Graph axes at different scales 51 Camp Lake and Twin Lake have both experienced minor land use disturbances in their contributing lake catchments. There was no noticeable impact on sedimentation associated with those disturbances. 4.5 Nass Basin and Major Valleys Region 4.5.1 Description of Study Area Areas classified in this region include low-lying depressions and large valley flats located between major mountain ranges. The Nass Basin and the Skeena, Bulkley and Kispiox Valleys comprise most of this area. Rivers presently occupy these regions, but during pleistocene glaciation they served as channels down which glacier ice moved. The region contains hummocky, rolling, and undulating terrain underlain by thick Quaternary sediments. The broad valley bottoms range from 200-500m in elevation and have gentle relief. Coastal western hemlock is the dominant biogeoclimatic zone for the region. Climate ranges from the maritime environment of the coast to the continental interior climate inland. The study region consists of flat, low-lying areas of the Kalum, Kispiox and Bulkley forest districts. Most of this region is road accessible and has been subject to timber harvesting activities. 4.5.2 Description of Study Lakes Eighteen study lakes were selected from the Nass Basin and Major Valleys region. The Nass Basin and Major Valleys region and the location of the study lakes were shown in Figure 4.1. Maps of the lake catchments are included in Appendix F. The lakes in this region are relatively small compared to those in the other study regions. The lakes located in the major valleys are impounded by thick Pleistocene deposists. Lakes in the Nass Basin occupy low plateaus in a series of glacially scoured troughs running northwest-southeast. The majority of the littoral zone substrate of the lakes is composed of a thick veneer of organic fines. Alder and willow commonly line the lake shorelines. Wetlands and low-lying swampy areas are also common around the lakes. Mature forests of hemlock, balsam, and spruce dominate the upland areas. Distal to the lakes are high relief mountainous areas. Some of the catchments comprise enough mountainous area to have comparable landscape parameters to the mountain regions. The lakes, however, are not classified as being in the mountainous regions since they occupy broad valley bottoms or flat plateau areas. Landscape indices for the Nass Basin and Major Valley lakes are tabulated in Appendix B. Lake 13, Lake 4, Arbour, and Kwinageese West Lakes have all had no land use disturbances in their surrounding areas. All other lakes are in easily accessible areas and have had road construction and 52 timber harvest within the catchment. Big Fish Lake was the most heavily logged with 59% of the catchment logged and a road density of 3.85 km/km2. Other heavily disturbed lakes include Elizabeth, Flatfish, Hoodoo, and Mitten. A summary of land use disturbance for the Nass Basin and Major Valley lakes is included in Appendix C. 4.5.3 Lake Sediment Records Sedimentation rate profiles for the Nass Basin and Major Valley study lakes are included in Appendix D. Background mid-lake sedimentation rates range from 16 g/m2/yr in Kwinageese West Lake to 186 g/m2/yr in Unnamed KM1 Lake. Lakes with larger contributing areas generally have higher sediment loading rates. The background rates, however, are not well predicted by any linear combination of landscape variables. Unnamed KM1 Lake and Mitten Lake have some visible varving in their sediment cores. Varve counting from 18 to 20cm of depth in the Unnamed KM1 core revealed a sedimentation rate of about 180 g/m2/yr. The rate derived from 210Pb for that segment was slightly higher at 204 g/m2/yr. Varves in the Mitten Lake core indicated a sedimentation rate of approximately 135 g/m2/yr from 2 to 4cm of the sediment column. This is close to the 210Pb estimate for the same core segment of 147 g/m2/yr. Many lakes in the Nass Basin and Major Valleys Region have had episodic periods of high sedimentation rates. This suggests that although the lakes are situated in relatively flat terrain, disturbances in upland areas will still occasionally flush large amounts of sediment into the lake basins. Peaks in the sediment records commonly exceed background rates by 100-200%. In a few extreme cases the records show that peak rates reach levels almost 500% above background. Recall that the absolute magnitude of these peak sedimentation rates cannot be determined because of the limited resolution of the sediment records. Observed increases are underestimates of the actual peak values, due to the averaging of sedimentation rates over periods of many years. Duckwing, Niska East, Octopus, and Paw lakes have been added to the control group of undisturbed lakes because the degree of disturbance was very small or it occurred too late in the record to be able to see a response in the sediment record. Half of the control lakes show an increasing trend in sedimentation in the latter half of their sediment records (50 to 100 years), a similar trend to what was observed in the Skeena Region lakes. The increases above background levels range from 43% in Lake 4, to 161% in Arbour Lake. The remaining control lakes have some episodic fluctuations in their accumulation rates, but do not have this clear increasing trend over the last half of their sediment records. 53 Of the control lakes, Arbour and Kwinageese West were analyzed for organic content. Average organic content was 37% and 46% for the lakes respectively. The recent increase in sedimentation in Arbour Lake and the peak in sedimentation in Kwinageese Lake coincide with slightly higher levels of clastic sediment. The remaining ten lakes in the region have been subjected to forestry related land use disturbances. Two of the lakes, Unnamed KM1 and Derrick, will be excluded from further analysis because their sediment records are not continuous enough to interpret possible land use impacts. Of the remaining 8 lakes, 6 have an increase in sedimentation coinciding with road construction and timber harvest (Figure 4.12). The land use disturbances and increased rates of sedimentation are summarized in Table 4.3. The lakes with the highest number of stream crossings had the greatest increases in sedimentation. The elevated sedimentation rates following land use in Sandal Lake are minor relative to earlier rates recorded in the late 1800's and early 1900's for that lake. The remaining two lakes, Arrowhead and Flatfish, have had increasing sedimentation rates beginning well before any land use disturbance. Although all lakes have higher sedimentation rates following the forestry activities, several of the control lakes in the region show a similar trend in recent accumulation rates (Figure 4.13). This makes it difficult to determine to what degree the land use disturbances are impacting lake sedimentation rates. Table 4.3: Land Use Impacts of Selected Nass Basin and Major Valley Lakes Lake Name Logged Road Density* Stream Crossings % Increase in Sedimentation Notes Elizabeth 34% 1.2 13 307% Large portion of catchment logged and roaded, greatest number of road crossings Mitten 31% 1.0 4 247% Large portion of catchment logged and roaded, logging occurred on steep slopes adjacent to lake Pentz 5% 1.8 0 167% Catchment contains major access road Bigfish 59% 3.9 3 137% Very highly logged and roaded catchment Sandal 7% 0.7 0 100% Minor land use disturbance Hoodoo 32% 1.2 1 36% Large portion of catchment logged and roaded *Road densities are in km/km2 Figure 4.12: Sediment Accumulation Rates (SAR) of Selected Nass Basin and Major Valley Lakes SAR(g/nf/yr) BIGFISH SAR(gVmfVyr) ELIZABETH 1872 1892 1912 1932 1952 1972 1900 1920 1940 1960 SAR(g/mfVyr) HOODOO 100 1 SAR(g/nf/yr) 1868 1888 1906 1926 1946 1966 1986 PENTZ '1% 1910 1920 1B40 1950 1970 19S0 1990 SAR(g/rrf/yr) 1170 1190 400 1 SAR(g/rrfVyr) MITTEN 1950 1970 SANDAL \ s 1643 1363 1633 1903 1923 ' 1943 1963 1933 Shaded area shows time period following initiation of land use activities. Graph axes are at different scales. Figure 4.13: Sediment Accumulation Rates (SAR) of Selected Control Lakes SAR(g/rrfVyr) ARBOUR Trend 1 SAR(g/rrr7yr) PAW T r e n d ^ j f H—'• 1647 1867 1687 1907 1927 1947 1967 1987 1923 1933 1943 1953 1963 1973 1983 1993 55 Elizabeth Lake is the only lake that clearly shows a recovery of sedimentation rates following completion of land use disturbances back to background levels. A map of the lake catchment and a plot of sedimentation rates and land use history of Elizabeth Lake are shown in Figure 4.14. Notice that sedimentation rates begin to increase immediately following the initial road construction in the lake catchment. Sedimentation rates continued to rise while road construction continued and logging began north of the lake. The highest sedimentation rate of 374 g/m2/yr (307% above background) occurred two years following the most major road construction and significant logging in the catchment in 1980. Sedimentation rates began to recover when road construction in the basin was completed. Some timber harvesting activities continued through the falling limb of sedimentation. It is interesting to note that most of the catchment area is not directly connected by stream channels to Elizabeth Lake. Water draining from the large eastern portion of the catchment seeps through a wetland area as unchannelized flow to a stream that enters Elizabeth Lake. Very little sediment would be transported through this wetland zone. This isolates the contributing catchment area for terrestrial sediment to the small western portion of the catchment (separated by dashed line in Figure 4.14). This section of the catchment has been subject to intense forestry disturbances (52% of area logged and road density of 2.16 km/km2), and is clearly connected to the lake system. This may be a reason why the land use signal is so discrete for the lake. Although not as clear as in Elizabeth Lake, Mitten Lake also shows a similar recovery pattern following the completion of road construction in the catchment. Of the disturbed lakes, Arrowhead and Bigfish were analyzed for organic content. Arrowhead Lake had rapidly decreasing organic content in the top 5cm of the core (49% to 29%). The increasing sedimentation observed over that period is largely associated with increasing clastic yield from the catchment. Organic content in the Bigfish core was 49% in the early 1990's and 43% at the beginning of the century. This may be an indication that Bigfish Lake is more productive than it was 100 years ago. 4.6 Nechako Plateau Region 4.6.1 Description of Study Area The Nechako Plateau is the only extensive plateau region in northwestern British Columbia. The Bulkley River extends southeastward into the Nechako Plateau, a rolling region with elevations ranging from 800 to 1200 meters. The Nechako Plateau is bordered on the west by the Hazelton Mountains and to the north by the Skeena Mountains. The Nechako Plateau makes up part of the Interior Plateau region of British Columbia. This region contains the least dramatic relief of all of the study areas. Flat-lying volcanic strata and glacial drift overlie older bedrock in this region. Rivers flow in deep, glacially modified valleys cut into the rolling uplands. Lakes and wetlands dot the landscape in poorly drained, Figure 4.14: Elizabeth Lake Sedimentation Rates, Land Use History, and Catchment Map 56 ELIZABETH LAKE ELIZABETH Sedimentation Rate (g/nf/yr) N ] Road Density (knVknf) # of Stream Crossings nik i In Hi % Logged Basin Core Roads Rivers Cuts Lakes Wetland 1000 1000 2000 Meters 57 postglacial depressions. The dominant biogeoclimatic zones include sub-boreal spruce to the north and Cariboo aspen-lodgepole pine to the south. The region contains all of the Lakes forest district and portions of the Morice and Bulkley forest districts. Most of this region is road accessible and has been subject to timber harvesting activities. The climate of Nechako Plateau is continental, and is characterized by seasonal extremes of temperature and moderate annual precipitation. Summers are relatively warm, moist and short with a mean daily July temperature of about 15°C. Winters are generally severe and snowy with temperatures below 0°C for about 5 months of the year. Mean annual precipitation is about 500mm, of which close to 50% is snow. Precipitation is distributed relatively uniformly throughout the year. 4.6.2 Description of Study Lakes Nineteen study lakes were selected from the Nechako Plateau region. The Nechako Plateau region and the location of the study lakes were shown in Figure 4.1. Maps of the lake catchments are included in Appendix F. The largest range of lake and lake catchment sizes are found in this region. The lakes occupy post glacial depressions and are fairly regular in shape and are relatively shallow, and they are in a more advanced successional stage compared to the lakes in the other study regions. Low lying and poorly drained peat bogs, marshes and swamp areas are common. There is a high degree of beaver activity surrounding the lakes. Small lakes and ponds are abundant in the study catchments, many being held behind old beaver dams. There are no signs of hillslope coupling in the relatively flat terrain of this region. Coniferous forests of pine, spruce and fir dominate the catchments, with some patches of deciduous growth also present. Two sampling sites were required for Binta and Tanglechain lakes because they contained distinct double basins. Pine Tree, Doris, Boomerang, and Tanglechain lakes comprise a cascading lake system. Landscape indices for the Nechako Plateau lakes are included in Appendix B. Lake 10 is the only lake that has had no land use disturbance in the region. Haney has had a minor trail built through its catchment, and Ligitiyuz contains only a small corner of a cutblock, so they are also treated as control lakes. Road construction and timber harvest is extensive throughout the region. The catchments with the greatest amount of logging activity are Bristol (43% logged, road density of 1.43 km/km2), Horseshoe (34% logged, road density of 1.43 km/km2), and Parrot (33% logged, road density of 1.20 km/km2). A large forest fire north of Parrot Lake in 1983 burned about 50% of the lake catchment area. Smaller bums have also occurred near Binta, Boucher and Takysie lakes. The land use history surrounding Takysie Lake is much longer and more diverse than the other lakes. The time of first human settlement is unknown, but most development is known to have occurred since 1930. The most intensive 58 logging occurred in the 1970's and 80's. Other issues of concern for Takysie Lake are shoreline and streambank erosion from grazing animals, and water quality degradation by leaking septic systems, runoff from animal waste, fertilizers, and residential and resort/campground use. A summary of land use disturbance for the Nechako Plateau lakes is included in Appendix C. 4.6.3 Lake Sediment Records Sedimentation rate profiles for the Nechako study lakes are included in Appendix D. Background mid-lake sedimentation rates range from 30 g/m2/yr in Takysie Lake and Lake 10 to 280 g/m2/yr in Boucher Lake. As observed in the other regions, lakes with a larger contributing area generally have higher sediment loading rates. However, similar to the Nass Basin and Major Valleys region, background sedimentation rates are not well predicted by any linear combination of landscape variables. There is no visible varving in any of the sediment cores from this region. Sedimentation rates in the Nechako Region lakes are less variable than observed in other regions. Episodic transfer of large quantities of sediment into the lake basins is not as common, as mass wasting events are less likely in this relatively flat terrain. There are, however, a few cases where substantial peaks in sedimentation rates are observed in the sediment records. Notable peaks have occurred in Parrot (240% above background), Lake 31 (369% above background), Haney (310% above background), Clota (at least 200% above background), and Boucher (95% above background) lakes. Lakes in the Nechako region show similar patterns in lake sedimentation as observed in the Nass Basin and Major Valleys. Two of the four control lakes have had increasing sedimentation rates over the last several decades (Lake 8 - up to 92% above background, and Lake 10 - up to 117% above background). This natural increase in sedimentation rates has been observed in about half of the control lakes in this study, making the interpretation the land use effects on the sediment signatures significantly more difficult since the timing of this increasing trend coincides closely with land use impacts. Ligitiyuz and Haney, both control lakes, have been analyzed for organic content. Average organic content was 27% and 48% for the lakes respectively. Ligitiyuz Lake showed a slow increase in organics, from 24% to 31% by mass over the last 150 years. Organic content in the Haney core shows some fluctuations over time, but no consistent trend is apparent. Ten of the twelve lakes that have experienced forestry related land use disturbances have coinciding increases in their sedimentation rates (Figure 4.15). Clota and Lake 31 had increasing sedimentation rates before the onset of forestry activities. Excluded from this analysis are Binta, Parrot, and Takysie lakes, which have had more complex disturbance histories and are discussed as individual Figure 4.15: Sediment Accumulation Rates (SAR) of Selected Nechako Plateau Lakes SAR(g/rrfVyr) BITTERN 157 1177 1117 1>17 1937 1937 1977 1997 SAR(g/rrrVyr) DORIS 1882 1S02 1922 1942 1962 350 -j SA R{g/mrVy r) PI NETREE 1859 1679 919 1939 r . SAR(g/rrf/yr)TANGLECHAIN BASIN A eoo-i SARfg/rrrVyr) BOOMERANG 4so-i SAR(g/rrrVyr) BRISTOL 873 1893 1913 1933 1953 1973 SAR(g/nrr7yr) HORSESHOE 1940 1850 I960 1970 1980 ^SARtg/rrrVyr) TORKELSEN 1651 1671 1891 1911 1931 1951 . SAR(g/rrrVyr)TANGLECHAlN BASIN B 1173 1195 1911 1915 1955 1175 1913 1913 1913 1953 195! 1973 1913 1913 Shaded area shows time period following initiation of land use activities. Graph axes are at different scales. 60 cases later in this section. Summaries of the lake disturbances are included in Table 4.4. Catchments with greater land use disturbances generally show greater increases in sedimentation, but this relation doesn't hold for all lakes. Stream crossings for Boomerang, Doris, and Tanglechain lakes are high because lakes comprise a cascading system below Pine Tree Lake. Table 4.4: Land Use Impacts of Selected Nechako Plateau Lakes Lake Name % Logged Road Density* Stream Crossings % Increase In Sedimentation Notes Pine Tree 19% 1.0 9 295% Moderately disturbed catchment, high number of road crossings relative to catchment size Bristol • 43% 1.4 24 286% Large portion of catchment logged and roaded Torkelsen 12% 0.9 12 285% Moderately disturbed catchment Horseshoe 34% 1.4 53 219% Large portion of catchment logged and roaded Tanglechain B 19% 1.2 84 181% Moderately disturbed lake catchment, contains major access road Bittern 6% 0.7 1 137% Minor disturbance in lake catchment Boomerang 12% 1.0 21 131% Moderately disturbed catchment, contains major road close to lake with multiple stream crossings Tanglechain A 21% 1.2 88 120% Moderately disturbed lake catchment, contains major access road Doris 19% 1.2 83 90% Moderately disturbed lake catchment Boucher 5% 0.2 0 43% Minor disturbance in lake catchment *Road densities are in km/km2 The cascading lake system is situated about 30km east of Smithers. These lakes with their contributing catchment areas are show in Figure 4.16. The cascading system shows the effects of downstream sediment storage through the lake cascade. Specific sediment yield (yield per unit area of contributing area) decreases significantly from Boomerang to Doris (0.24 -> 0.008 Mg/m2/yr), and from Doris to Tanglechain basin B (0.008 -> 0.002 Mg/m2/yr). Minor increases in Boomerang and Tanglechain basin A are likely due to sediment focusing in Boomerang (more narrow, trench shaped Figure 4.16: Pinetree - Boomerang - Tanglechain Cascading Lake System 61 Specific Sediment Yield: Pinetree - 0.018 Mg/km 2/day (moving down cascade) Boomerang - 0.024 Mg/km 2/day Doris - 0.008 Mg/km 2/day Tanglechain Basin B - 0.002 Mg/km 2/day Tanglechain Basin A - 0.004 Mg/km 2/day 62 basin) and a higher trap efficiency in Tanglechain basin A (larger basin located further from inflow). All lakes have had forestry activities within their lake catchments, and all show increasing sedimentation rates following the forestry disturbances (shown in Figure 4.15). There does not appear to be any cumulative effects in sedimentation down the lake cascade system because lakes act as efficient sediment traps. Sediment cores from Pine Tree, Boomerang, and Doris lakes have all been analyzed for organic content. Average organic content decreases moving down the cascade, with organic contents of 39%, 32%, and 26% for the lakes respectively. Only the Pine Tree lake sediments showed any temporal trend in organic content with an increase of about 8% over the last 150 years. Binta Lake is a large double basin lake located in the southeast corner of the study region. The lake catchment and sediment profiles are shown in Figures 4.17 and 4.18. Specific yield is significantly lower in Basin A due to the high storage capacity of Basin B on the upstream side of the lake. There were two bums east of Binta Lake in 1934 (40km2) and 1965 (2km2). These burns had no significant impact on sedimentation rates in the lake. There has been extensive forestry activity around both basins of the lake. Both basins have had increasing sedimentation rates following road construction and timber harvest in their contributing areas. In Basin A sedimentation rates increased following road construction and timber harvesting in the early to mid 1960's. Rates peaked at 285 g/m2/yr (119% above background) in 1981 after significant road construction and logging during the 1970's. Sedimentation rates began to decrease, but began increasing again to 280 g/m2/yr (115% above background) following significant cutting in the early 1990's. Sedimentation rates in Basin B also appear to be related to land use in upstream areas. The fluctuations are not as sharp as those observed in the other basin, possibly due to the buffering effects of lakes upstream of Basin B. Sedimentation rates increased to 307 g/m2/yr (105% above background) following intermittent road construction and timber harvest through the 1950's and 60's. Rates increased again to 356 g/m2/yr (137% above background) after more significant road construction and logging activities through 1980's and 90's. Sediment cores from both basins in Binta Lake were analyzed for organic content. Average organic content was 28% and 24% for Basin A and B respectively. Both basins show an recent increase of organic content, possibly related with land use in the catchment. Sediments from Basin B were also analyzed for particle size distribution. The sediment was primarily composed of very fine to coarse silts (2um - 32(im). A smear slide sample showed that the sediment contained a large amount of organic matter and diatom silica. Parrot Lake is a large lake located about 30km south of Houston. The lake catchment and sedimentation profile are shown in Figure 4.19. A significant peak occurred in the sediment record in the 1940's. The cause of this disturbance is undetermined. Following that disturbance there has been a significant burn of 51% of the catchment area, and a large amount of road construction and timber harvesting surrounding the lake. Despite these large-scale terrestrial disturbances in the contributing Figure 4.18: Binta Lake Sedimentation Rates and Land Use History 64 Road Density # of Stream Crossings 3 n n n % Lo g g ed SAR(g/mfVyr) BINTA BAS IN B Forest tire (1%of catchment burned) Forest fire (29%of catchment burned) 1905 1915 1925 1935 1945 1955 1965 1975 19S5 1995 , 4 Road Density # of Stream Crossings 1% Logged Figure 4.19: Parrot Lake Sedimentation Rates, Land Use History, and Catchment Map 65 66 areas to the lake, sedimentation rates have increased by only about 50%. This is a small increase in sedimentation, relative to what has been observed in other Nechako Plateau lakes following land use disturbances. A cascade of three small lakes upstream of Parrot, ranging from 0.23 to 0.27 km2 in size, may be buffering the disturbance impacts to the Lake. Takysie Lake is another large Nechako Plateau lake that has had a long and diverse land use history. Takysie is located about 15km west of Binta Lake in the southeast corner of the study area. The lake catchment and sediment profile are included in Figure 4.20. Sedimentation rates in Takysie lake have been increasing since 1865, the earliest date available from the 210Pb analysis. Most of the increase has occurred following road construction, timber harvest, and other land use activities, including animal grazing, agriculture, residential development, and resort/camping. The time of first land use disturbance is unknown, but most development is known to have occurred since 1930, primarily to the west of the lake. The sediment profile does not reach a level background rate. 2 I 0Pb analysis done in a paleolimnological assessment of Takysie Lake by Reavie and Smol (1998) indicated a background sedimentation rate of about 30 g/m2/yr. This background rate fits the trend observed early in our sediment record. Both results showed a similar increase in sedimentation rates over the latter part of the century. Our results gave a higher peak sedimentation rate of 269 g/m2/yr compared to about 210 g/m2/yr in their study. Sedimentation rates have increased 600 to 800% above background in Takysie Lake over the last 150 years. Not all of this increase can be linked to land use because rates were increasing before land use activities began in the catchment. However, an increase of this magnitude is unprecedented for the lakes in this study. Reavie and Smol (1998) attributed the increasing sedimentation rates to lake eutrophication caused by elevated nutrient input from human settlement surrounding the lake. 68 5 OBSERVED PATTERNS IN LACUSTRINE SEDIMENTATION 5.1 Introduction Patterns and trends in lacustrine sedimentation over the entire study area are presented and discussed in this chapter. Included are analyses of within-lake spatial variability, varved records, regional variability, temporal variability, and land use impacts on lake sedimentation in Northwestern British Columbia. 5.2 Within-Lake Spatial Variability A minimum of four cores were sampled from the deepest point of the central basin of each lake. Whenever possible additional cores were taken at points located elsewhere in the lake basin. A visual comparison was made in the field between all the cores taken from each lake. If the sediment cores contained visual markers (event layers, varving, change in sediment character, etc.), then the assumptions of areal continuity and synchroneity of the lake sediments could be verified. Lake sediments must have these properties for cores to be representative of deposition across the entire lake. If the assumptions of areal continuity and synchroneity are valid, sediment properties will be consistent and deposited in similar proportions over the whole lake area. Cores from the same lake should then all have a similar and consistent sediment structure. There were no cases where the assumptions of areal continuity and synchroneity of lake sediment did not appear to be valid for mid-lake areas. The focusing of sediment to deeper lake areas was evident because the distance between horizons in the sediment cores usually decreased as cores were sampled in shallower water. In lakes with a relatively flat bottom the distance between horizons would increases as cores were sampled closer to the main inflow to the lake. The deepest spot in these lakes would not have been the optimal sampling location for obtaining the best temporal resolution in the lake sediment analysis. Cores taken in shallower water and from near shore locations would not always have a stratigraphy similar to that of the mid-lake cores. This was especially true in cores that were sampled on steep lake bottom slopes, above the lake thermocline, or on a delta front. These sediments are subject to resuspension and transport by sub aqueous slumping, water currents, and wind/wave action. Lakes best suited for this study have a well-defined and deep central basin, with a relatively flat bottom that is out of the influence of deltaic and nearshore processes. Lakes were selected that appeared to best meet these requirements in order to help assure areal continuity and synchroneity of the lake sediments. This was reflected in the high degree of correlation between mid-lake sediment cores. There is some concern that lake sediments from some of the shallower lakes with high fetch could be subject to mixing by 69 wind/wave action. This could degrade the sediment signatures of terrestrial events in the lake catchment. The critical depth where accumulation of sediments prevails over transportation processes by wind/wave action may be estimated using the simple empirical equation below. Although this equation has not been tested for lakes in the Pacific Northwest, it is the only site-specific model available that is based on easily obtained morphometric variables. Its generality has been assumed since lake geometry is intuitively the main controlling factor in determining mixing potential. D T . A = (45.7»Lf)/(Lf + 21.4) (Hakanson and Jansson 1983) Where: D T . A is the critical depth (m) Lf is the potential maximum effective fetch (km) The study lakes have been plotted against this equation in order to identify lakes that could be subject to wind/wave mixing of bottom sediment (Figure 5.1). Takysie Lake is the only lake that lies above the critical depth limit. Lake 21, Bittern, and Kwinamuck Lakes are also very close to the critical limit. The mixing of bottom sediments can cause sediment parameters to be more diffused through the core. Therefore, the sediment profiles from these lakes could be less sensitive to terrestrial events in the lake catchments. Most lakes are well below the defined critical depth, so wind/wave mixing of sediments should not be a confounding factor in interpreting the sediment data. 5.3 Varved Sediments Seven of the study lakes had varving over a segment of their sediment cores. All the varved sediments were from North Coast lakes or from lakes in the northern portion of the study area. This suggests that the presence of glaciers and strongly contrasting summer and winter hydrologic conditions are important factors in the development of varving. All the lakes were strongly stratified at the time of sampling and had good sediment focusing characteristics. A comparison of averaged sedimentation rates derived from 210Pb dating and annual varve counting is included in Table 5.1 and Figure 5.2. Table 5.1: Comparison of Sedimentation Rates Calculated from 210Pb Dating and Varve Counting Study Lake Core Segment (cm) Averaged Estimated Sedimentation Rate (g/m2/yr) 210Pb Dating Varve Counting Toon 1-19 418 412 Figure 5.1: Plot of Study Lake Depth and Effective Fetch with Critical Depth Limit (Ij>_A) 70 Effective Fetch (km) 3 5 10 15 20 £ 25 a. u Q 30 35 40 45 50 , Bittern Lake # - ••- _ Lake 21 • • • • • • • * • • * • • • • • • • • .Takysie Lake Critical Depth • Study Lakes Figure 5.2: Comparision of Pb210 and Varve Counting Methods of Calculating Sedimentation Rates 3000 500 1000 1500 2000 Pb210 Dating 2500 3000 71 Amoth 14-30 2723 2533 Unnamed KM1 18-20 204 180 Jade 8-9 1075 1050 Alpha 6-12 60 76 Dragon 4-6 470 400 Mitten 2-4 147 135 There is a high degree of correlation between the averaged sedimentation rates calculated using both methods. The 210Pb calculated rates are slightly greater in 6 of the 7 lakes listed in Table 5.1. This bias may indicate a minor error in the estimation of the background 210Pb concentrations used in the sediment accumulation rate calculations. Nevertheless, the high agreement between the relative and absolute chronologies improves our confidence in the dating techniques used. Only Toon Lake contained consistent enough varving to plot changes in the sedimentation rate over time. The sediment accumulation plots for Toon Lake were shown in Figure 4.3. Clearly both plots showed similar trends in sedimentation over time. There were, however, moderate differences between the estimated background and peak rates of sedimentation for this lake. 5.4 Regional Variability Background sediment yield is a measure of the volume of sediment being deposited in the lake basins. Investigating relations between the sediment yield and landscape characteristics of the contributing basin is useful for developing predictive equations for estimating sediment yield in the general study area using easily obtainable drainage basin parameters, thus avoiding costly field sampling programs. Although this type of empirical analysis does not prove any cause-and-effect relations between sediment yield and landscape characteristics, these non-causal relations may represent important prologues to further theoretical understanding of the underlying physical processes of sediment transfer. A stepwise linear regression was performed with background sediment yield estimated from the 2 l 0Pb dating of the sediment cores (dependant variable) and all the GIS derived landscape indices for the lake inventory (independent variables). The regression was run for each physiographic region and for the entire data set. The regression results, including the ANOVA of the regressions are presented in Table 5.2. 72 Table 5.2: Background Sediment Yield Regression and ANOVA Results North Coast log(Y) = 0.76 + 1.381og(Ab) n = 9, R 2 = 0.86 F Value: log(Ab) -» 43.5*" Nass Basin and Major Valleys log(Y)= 1.09 + 0.5 llog(A„) n = 18,R2 = 46 F Value: log(Ab) -» 13.7" Hazelton Mountains log(Y) = 0.19 + 1.431og(Ab) - 0.661og(VFA) n = 16, R 2 = 0.83 F Values: log(Ab) -» 50.7*", log(VFA) -» 11.2** Nechako Plateau log(Y) = 1.42 + 0.431og(Ab) n = 21,R 2 = 0.47 F Value: log(Ab) -M6.6*" Skeena Mountains log(Y) = 1.12 + 1.841og(Ab) + 0.62DD n= 12R2 = 0.84 F Values: log(Ab) 39.3"*, DD -> 8.3* AH Regions log(Y) = 0.59 + 0.771og(A„) + 0.521og(slope) n = 76, R 2 = 0.66 F Values: log(A„) -> 134.1***, log(slope) -» 8.0** Where: Y is the background sediment yield (Mg/yr) * P < 0.05 A b is the area of the drainage basin (km2) ** P < 0.01 VFA is the total valley flat area upstream of lake including water bodies (km2) *** P < 0.001 D D is the drainage density (km/km2) Slope is the mean slope of the land surface area (degrees) All of the regression line slopes are highly significant (P = 0.001). In all cases the drainage basin area is the most important predictor variable. Sediment yield in the North Coast region is well predicted by the contributing drainage basin area. Total valley flat area and drainage density were important variables in the Hazelton and Skeena Mountain regions respectively. Valley flat area is a term describing storage potential in the catchment. Valley flat area is defined as the sum of continuous, flat-lying (less than 1 degree slopes) land and water body (upstream wetlands and lakes, excluding the study lake) areas in valley bottom areas of the lake catchment. These are areas where net accumulation of sediment reservoirs occurs. Therefore, catchments with large valley flat areas are more likely to have lower sediment yields, hence the negative influence on yield in the Hazelton Mountains. Conversly, drainage density had a positive influence on yield in the Skeena Mountains as term that describes the transport capacity of a catchment. Since fine sediment is transported in suspension through stream channels, catchments with greater stream lengths per unit area will more efficiently transfer mobilized sediment from the land surface, through the stream network, to the receiving lake downstream. Sediment yields in the Nass Basin and Major Valleys region and the Nechako Plateau region are not well predicted by any linear combination of the landscape indices. With the complete data set, drainage basin area and mean slope of the catchment were the most significant predictor variables. It is not surprising that slope emerged as a significant variable in the all regions regression. Average slope of a catchment relates to both storage potential (negatively - sediment accumulation is more likely to occur in flat-lying terrain) and transport capacity (positively - steep terrain is more likely to be the source or transport area of 73 sediment) of the basin. It is unclear if the regression results for all regions combined makes sense when the regional component regressions yield different results, which implies the possibility of different underlying physical processes in the different regions. It is interesting to note that the R2 values are the highest in the mountainous areas (North Coast, Hazelton Mountains, and Skeena Mountains). The greater storage potential of sediment in the flatter catchment areas (Nechako Plateau, Nass Basin, and Major Valleys) may be confounding the predictability of sediment yield. Specific sediment yield, or sediment yield per unit of contributing basin area, is used as an index of primary subareal denudation of the lake catchments. Lake-to-lake and regional comparisons in catchment denudation rates can be made using specific yield since it accounts for basin scale and areal focusing of sediment into the receiving lake. Specific yield ranges from 0.0015 Mg/km2/day from the Tanglechain Lake Basin B catchment in the interior, to 0.1434 Mg/km2/day for the Amoth Lake catchment in the Coast Mountains. The average specific yield over all the lake catchments is 0.028 Mg/m2/yr. The average specific yields for the different physiographic regions are plotted in Figure 5.3. ANOVA indicated a statistical difference in the regional specific yield means. The North Coast region was shown to have a statistically greater mean specific yield compared to the other regions using Tukey's test (alpha = 0.01). The higher rate of sediment yield per unit area in the North Coast reflects the higher erosion rates due to the greater transport capacity and lower storage potential in that region. These characteristics of the North Coast region are reflected in the landscape variables of mean slope and valley flat area shown in Figure 5.4. The North Coast lake catchments have significantly steeper slopes and less valley flat area than the other study regions. In British Columbia, it has been proposed by Church and Slaymaker (1989) that specific sediment yield increases at all spatial scales up to 3 x 104 km2. The dominance of secondary remobilization of Quaternary sediments in larger drainage basins is the cause of this scale effect. Specific sediment yield for fluvial suspended-sediment-transport records in British Columbian rivers and lake sediment-based yields from this study are plotted as a function of drainage area in Figure 5.5. Open symbols in the diagram indicate catchments that contain large lake and/or wetland areas upstream of the study lake. In these lakes yields are strongly influenced by upstream storage processes. The trend for the lake/wetland controlled basins over the spatial domain of this study shows specific yields declining as the area drained increases, roughly proportional to (drainage area)"0'7, indicating the dominance of sediment storage in larger catchments. Most of the lake sediment derived yields from non-lake/wetland controlled basins for northwestern British Columbia lake catchments fit the Church and Slaymaker (1989) envelope defining the main trend in specific sediment yield. The few lakes that plot below the lower envelop limit are all located in flat valley bottom or plateau regions where footslope and floodplain storage is likely sufficient Figure 5.3: Regional Differences in Specific Sediment Yield Hazelton Mountains Skeena Mountains Nass Basin and Major Valleys Error bars show 2 standard errors Nechako Plateau ' Significant difference from other groups (Tukey's test, alpha = 0.01) Figure 5.4: Regional Differences in Mean Slope and Valley Flat Area of Lake Catchments 30 Coastal Mountains Hazelton Mountains Skeena Mountains Nass Basin and Major Valleys Nechako Plateau Coastal Mountains Hazelton Mountains Skeena Mountains Nass Basin and Major Valleys Nechako Plateau Error bars show 2 standard errors ** significant difference from other groups (Tukey's test, alpha = 0.01) 75 76 to influence downstream sediment yield. There is no apparent trend in the non-lake/wetland controlled basins when the yields are not stratified regionally. The data used to plot the general sediment yield trend for British Columbia in Figure 5.5 are sparse for drainage areas from 1 to 100 km2 (8 data points). A closer look at spatial trends between these scales can be made using the lake catchment yields, which consists of 70 lake catchments ranging from 0.93 km2 to 186 km2. Some interesting patterns are apparent when the data set is stratified regionally as shown in Figure 5.6. The first plot in Figure 5.6 shows spatial trends in specific yield for the North Coast study catchments. These are high-energy systems that contain very steep terrain and receive large amounts of precipitation. Upland slopes are thinly mantled with large areas of exposed bedrock. Storage potential is low since there is relatively little flat terrain in the contributing catchments of the lakes. Sediment yield increases with drainage area for lake catchments in this region. Sediment yield is roughly proportional to (drainage area)0'6. This fits the Church/Slaymaker model of sediment yield where remobilization of Quaternary sediment dominates sediment transfer in the basin. Pleistocene deposits on lower valley slopes (fans and aprons) and valley bottom areas are likely the predominant sediment sources for lakes in the North Coast region. The third plot in Figure 5.6 shows spatial trends in specific yield for the Nechako Plateau, Nass Basin, and Major Valley study catchments. These are much lower energy systems with gentle relief and a drier continental climate. Upland slopes are mantled by thick glacial deposits. Lakes, wetlands, and broad valley flat areas are common upstream of the study lakes. Storage potential is, therefore, quite high in these areas. Sediment yield decreases with drainage area for lake catchments in these regions. Sediment yield is roughly proportional to (drainage area)"0'5. This trend fits the conventional model of sediment yield where sediment mobilized from upland areas goes back into storage on footslopes, floodplains, and water bodies further downstream. The cascading lake systems discussed in chapter 4 illustrate the storage effect as sediment is transported through the catchments. The second plot in Figure 5.6 consists of yields for the Skeena and Hazelton Mountain study catchments. The landscape characteristics of this region are intermediate to the regions shown in the first and third plots of Figure 5.6. A weak decreasing trend in specific sediment yield with drainage area is observed in these regions. Sediment yield does not clearly fit either of the two models mentioned above. Storage process may slightly dominate resulting in the small negative slope observed in the plot. In all regions the range of specific sediment yield spans an order of magnitude at all spatial scales, likely the consequence of local geology. Regional variability in the organic content of sediment and particle size is only briefly investigated herein because of the limited analysis of those sediment parameters. Average organic Figure 5.6: Specific Sediment Yield as a Function of Drainage Basin Area Stratified Regionally 0.1 0.01 0.001 Coast Mountains = f(A b) 0 6 • 0.1 10 100 1000 CO T3 E _; O ) _ > -•*—' c E T3 <D C O O * _ 'o a co 0.1 0.01 0.001 0.1 10 100 1000 0.1 0.01 0.001 Nass Basin, Major Valleys and Interior Plateau • Y = f(Ab)-°5 0.1 1 10 100 Drainage Area (km2) 1000 All trend lines fit by eye 78 content of sediment from the study lakes in northwestern British Columbia was highly variable, ranging from 5 to 55%, with an average organic content of 32%. Comparisons between physiographic regions are not possible due to the limited sample size of lakes tested for organic content. A relation between organic content of lake sediments and the catchments drainage area, mean slope, and mean elevation was found through stepwise regression of all analyzed lakes: %organic = 83.79 - 12.621og(Ab) - 24.331og(slope) - 0.0168elevation n = 20, R 2 = 0.78 F Values: log(Ab) -» 35.0***, log(slope) -> 14.0**, elevation -» 6.5* The data set is too small for this to be a reliable predictive formula. The inverse relationship of organic content with drainage area, slope, and elevation is, however, statistically significant. Detailed particle size analysis was carried out on a small, high-energy coastal lake (Toon) and a large, low-energy interior lake (Binta) to investigate differences in the sediment caliber for the two strongly contrasting study lakes. Sediment from Toon Lake was primarily composed of medium silt to fine sand (8 - 250|jm). Sediment from Binta Lake was primarily composed of very fine to coarse silt (2 -32|im). Generally, most of the lake sediment samples were observed to be primarily within the silt range. Sediment appears to become finer as lake and catchment size become larger, distance from the coast increases, and in less mountainous terrain (movement from high- to low-energy systems). Occasionally, sediment sizes up to medium sand were observed in event layers in sediment cores sampled from lakes in mountainous areas. These coarser sediments are probably associated with periodic, large magnitude events of sediment transport (extreme storms, mass wasting, etc.). 5.5 Temporal Variability Sediment transfer in headwater catchments of British Columbia is commonly dominated by large-scale episodic events, in which large volumes of sediment are flushed through the system over relatively short periods of time. These high-magnitude/low-frequency events include processes such as mass wasting, stream bank failures, and breaking of log jams. In the case of lake sedimentation, autochthonous processes could also be the cause of large fluctuations in sedimentation rates, including physical and biological events such as turbidity currents off a slumping delta front, or changes in lake productivity. The analysis of these disturbances is restricted because the sampling techniques used lack the temporal resolution to properly capture these events, especially if they occur early in the sediment records. Another problem in dealing with these low-frequency disturbances is that the sedimentary records are too short to address the overall importance of these events in drainage basin sediment transfer. 79 Over a third of the study lakes had a significant peak (any recorded sedimentation rate approximately 100% or greater above the estimated background rate) in their sedimentation rate profile without the influence of any land use activities occurring in the basin. While these peaks in the sedimentation rates may be indicators of significant natural disturbances in the lake catchment, the specific causes of these fluctuations is unknown. The peaks in sedimentation may be triggered by climatic events, but the network of meteorological stations in the region is too sparse to investigate this possibility (long term records are only available for Prince Rupert, Terrace, and Smithers; there are no records available in remote and mountainous areas where a large portion of the study lakes are located). These occurrences are most common in the mountainous regions, although they are observed in all regions. A closer look at the sediment profile of Shea Lake, a lake with a well-captured disturbance event, is made in Figure 5.7. Over a nineteen year period (1929 - 1948), sedimentation rates in Shea Lake increased to a peak rate ten times greater than background. During that time about half of the total sediment load since 1920 was deposited in the lake basin. Many of the sediment records show a significant increase in lake sedimentation rates over the latter half of the century. This trend has been observed in all study regions. Of the control lakes, 11 of 23 clearly show this increasing trend in sedimentation rates, with increases ranging from 30% to 167% above background levels. Some lake catchments that have had land use disturbances show the same increasing trend beginning before the onset of land use in the catchment. On average, sedimentation rates have been increasing irrespective of land use change in the study lakes for the last 50 years. Some of the lakes have had increasing organic content over the last century, but the increase has not been consistent or great enough to explain this trend in sedimentation. Particle size work in two of lakes that show the largest natural increase in sedimentation rates, Beta (167% increase) and Farewell (152% increase), showed that the sand content of the lake sediment has increased over the same period of time. The sand component (> 63pm) has increased from 46 to 54% in Beta Lake, and increased from 47 to 54% in Farewell Lake. This is an indicator that the transport capacity in the lake catchments may have been increasing over the latter half of the century. This could be a response to climatic change in the region. A relation between sedimentation rates and precipitation would be expected, since the hydrologic cycle is the major driving force in sediment transfer. To investigate this possibility, precipitation records for the region (included in Appendix G: Prince Rupert - 89 year record, Terrace - 85 year record, and Smithers - 55 year record) have been analyzed. Cumulative departure plots were used to identify periods of above and below normal annual precipitation (Figure 5.8). An increasing trend in sedimentation rates would be expected to Figure 5.7: Natural Disturbance in Shea Lake Sedimentation Sedimentation Rate 1920 1930 1940 1950 1960 1970 1980 1990 2000 ( L U L U ) uoiiEudpaJd |enuuv |Bio_ 82 coincide with above average periods of precipitation. The plots for Prince Rupert and Terrace show a similar pattern of below average or average precipitation for the first half of the century followed by above average precipitation. Both locations have also experienced precipitation significantly above normal for the last 20 years. Smithers, which is located in the interior portion of the study area, shows a different pattern in annual precipitation: rates have been above normal for the periods 1955 to 1965 and 1987 to present, with an intervening period of below normal precipitation between 1965 and 1987. These plots show that precipitation has been above average in the coastal areas for the last 50 years, and high above average over the entire region for the last 15 to 20 years. This indicates that the increasing trend in sedimentation rates may be, at least partially, a consequence of climatic trends in northwestern British Columbia. 5.6 Impacts of Land Use The majority of lake catchments in this study have been subject to road construction and timber harvesting activities. Most of these activities have occurred in the last couple decades. In most cases a significant increase in mid-lake sedimentation rates has coincided with these land use disturbances. However, since about half of the control lakes have also had an increase in sedimentation rates over the last few decades, the extent to which forestry has impacted lake sedimentation is uncertain. Of the control lake set, 48% (11 of 24) have had a recent increase in sedimentation rates. The average increase was 90% above background rates with a maximum observed increase of 167%. For lakes that have been subject to road construction and timber harvesting, 84% (32 of 38) have had increasing sedimentation rates. The average increase was 137% above background rates with a maximum observed increase of 307%. The largest recent increases in sedimentation rates have occurred in lakes of the Nechako Plateau and the Nass Basin and Major Valleys regions. These are the regions that have also experienced the greatest amount of forestry activity, because of their less rugged terrain and greater accessibility. Overall, lakes that have had road construction and timber harvesting in their watersheds have experienced greater increases in mid-lake sedimentation rates than the control lakes. In addition to forestry, other major land use disturbances have occurred in two of the study catchments. A mining operation was active north of Aldrich Lake from the early 1920's to 1954. Human settlement began west of Takysie Lake early in the century and was followed by ranching, agriculture, residential development, and resort/camping activities. The sediment records for both Aldrich and Takysie Lakes show significant increases in sedimentation over the duration of these land use disturbances. Although sedimentation rate increases coinciding with land use disturbances are easily identified they are well below the maximum relative increases observed, which are likely associated with natural geomorphic events. There was no clear relation between organic content of the sediment and land use activities. 83 The recent natural trend of increasing sedimentation rates observed in about half of the control lakes is a major confounding effect in the interpretation of land use signals in the sedimentary record. To separate, to some extent, this trend and natural episodic events from the sedimentation rate profiles, the graphs in Figure 5.9 were developed. The first graph plots the departure of sedimentation rates from background levels for control lakes using smoothed lines with large peaks filtered out. Jade Lake was removed from the set because it had a unique decreasing trend in its sedimentation rate profile. The remaining control lake profiles were used to define an envelope of naturally occurring sedimentation rates. The wedge-shaped envelope clearly shows the increasing trend in sedimentation rates observed in many of the control lakes over the last 50 years. Beyond the envelope limits are regions defined as unusually high and low sediment accumulation rates. The second graph shows the departure from background sedimentation for lakes that have had land use disturbances in their contributing catchment areas. All lakes that have not experienced sedimentation rates outside the envelope limits produced from the control lake data set have been removed. No disturbed lakes plotted below the lower envelope limit. Thirteen lakes were identified to have unusually high sedimentation rates because they plotted above the upper envelope limit. These unexpectedly high sedimentation rates are likely related, at least partially, to land use disturbances in the lake catchments. Details of the disturbance magnitude and sedimentation response are included in Table 5.3. 84 it i _ =J c TO C L •o 200 150 100 50 -50 • smoothed sedimentation rates since 1930 • extreme event peaks filtered out • Jade Lake removed from control set Figure 5.9: Separating Natural Trends and Land Use Impacts from the Sediment Records Control Lakes 500 450 400 T5 350 I 300 1 250 E o Unusually high sedimentation Unusually low sedimentation 1930 1940 1950 1960 1970 1980 1990 Disturbed Lakes 500 450 -400 -o c 350 -=1 c D l 300 -o JO E 250 o i— CD 200 • tr CB C L 150 -CD " D 100 -50 -0 -50 -smoothed sedimentation rates since 1930 - lines plotted for post disturbance period Expected sedimentation rate envelope 1930 1940 1950 1960 1970 1980 1990 •Binta •Mitten - Bristol - - - Pinetree •Gordeau Torkelsen •Horseshoe 1 McBride CD X> B o co <2 S3 O O H CO -4-1 cd C o 3 S 3 o % 4-4 s CO S xi co on X) CI •c co 4-4 O CJ o c cd 43 X) C CJ CD £ 4-4 CJ 43 1/1 3 O Pi tu es H s o O H CO CO & a o c co a XI 00 co XI 3 1 cd co co co 60 _ cd cd II Q o 2 2 IPS' • a r t 43 O H -a 43 00 # 43 ""H cd -D 3 « 3 O co VO — 4-1 <» " 1-1 o in c -a o CO D, 43 © 00 £ 3 CO O T3 3 3 O in 00 M % 43 > O •s 00 3 a cd SO 10 • o CN O N CJ > cd I o 43 t! o 3 O N fS g M -X) O 43 cd cj, -^1 « fll l_. 00 O H S iB rt <! 1 -4*1 N O C N O cd * J 43 -o o "ST S r 4—4 CO .O .ti o 00 s "2 c cj 43 O cd CO CJ 4-> cd 00 xt c 3 CJ aCJ CO CO cd 43 CJ 00 CO 43 .5 >^  4V cd 13 00 cd 3 CJ c £ 5 3 I c^ I—H cj > CJ •a X) cd o CJ 43 cd S E 00 O H o j f l < C/3 N O in o 43 cj cj cd cd 3 ,0 <*H CJ 00 > •S _g ,2 $ <+i 00 co CN II C eo O 4-4 SB S 3 •*H 4-4 -a 3 CJ CJ XI --3 CJ X) cd co t-l 45 3 CJ CJ 43 O O 00 O CJ ifi < & CJ > 4H T3 3 3 & 4 ? o cd 43 a C O O 2 cd 43 cj cj cd £ CL, o 00 U CJ a 00 3 •a 3 'ob C J 43 "cd 3 00 43 .a % CO CJ cd i-c •s § .2 ^ « 4 ? t! 43 to U —1 to ^ 3 3 00 43 3 « 31 • O Id cd O •a ^ ;a 'g oo 3 .a is O "ni 33 CJ 00 3 CN 0 o 3 3 co cc> 8 2 £3 CJ CO CO cn cd <-! 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Seventy lake catchments were selected for study that span a range of spatial scales, physiographic regions, and land use histories, in order to permit a comprehensive regional assessment of sedimentation trends and patterns for the study area. The objectives of the project were threefold: 1) Assess the natural patterns of lake sedimentation, including regional trends, spatial scale effects, and temporal variability; 2) Determine the relative impact of forestry on lake sedimentation in context with the naturally observed variability; and 3) Confirm the usefulness of lake coring and associated analysis techniques as appropriate methods of assessing long term impacts of forest harvesting and other land use disturbances on lacustrine sedimentation. The primary focus in the study has been on historical rates of lake sediment accumulation derived from 210Pb analysis of sediment core samples from the lakes. Some additional analyses were also carried out on selected study lakes, including organic content measurements, varve counting, and particle size work. Variables to describe the landscape and land use histories were extracted from a GIS database developed to inventory the study catchments. These variables and the lake sediment data have been analyzed to resolve the study objectives listed above. The key findings are reviewed in the nine points below. Also included in the points are references to the relevant thesis sections. The first seven points all pertain to the first study objective dealing with natural variability in lake sedimentation. The last two points address the second and third objectives, dealing with land use impacts and confirmation of the lake sediment methodology respectively. Key Findings: 1) There is a clear trend towards increasing lacustrine sedimentation rates irrespective of land use change in many of the lake catchments (Figures 4.11, 4.13, and 5.9). About half of the control lakes in the study clearly show increasing sedimentation rates over the last 50 years, with increases ranging from 30% to 167% above background levels. This natural trend is a major confounding factor in disentangling land use impacts on sedimentation patterns. This trend may be related to precipitation increases undergone in the whole study area over the last few decades (Figure 5.8). 2) Natural disturbances, such as mass wasting and other geomorphic events, are important processes of sediment transfer in headwater lake catchments (Figures 4.4 and 5.7). Sedimentation rate profiles from all physiographic regions show some periods of disturbed sediment accumulation where 88 accumulation rates are temporarily elevated many times above background levels. These occurrences are most frequent in mountainous regions. A large amount of the total sediment load delivered to lakes can be deposited over relatively short periods of time during these episodic events. Specific processes causing these disturbances in lacustrine sedimentation were undetermined in the study. 3) Some lakes had varved sediments, which provided an important absolute verification of the 210Pb dating results (Figures 4.3 and 5.2, and Table 5.1). Results indicated a high degree of correlation between both dating techniques. There was a slight positive bias in the 210Pb dating relative to the absolute chronology derived from varve counting. This may be caused by an error in estimating the background (supported) component of 210Pb in the sediment cores. 4) Organic content of the lake sediments is highly variable both spatially and temporally, ranging from 5 to 55% for the region. An inverse relation was found between organic content and drainage area, slope and elevation. Not enough lake sediments were measured for organic content to permit a complete regional assessment across the various physiographic regions in the study area. 5) Cascading lake systems in the study enabled estimates of trap efficiencies and storage effects. Lake basins act as effective sediment storage sites, indicated by decreasing specific sediment yields for lakes moving down the cascade system (Figures 4.7 and 4.16). In those two cases, upstream disturbances in sediment yield did not appear to propagate beyond lake areas (land use effects were non-cumulative downstream). 6) Double basin lake examples indicate the importance of lake morphometry on within-lake sedimentation patterns (Figures 4.6 and 4.17). Lakes with complex morphometries have greater within-lake variability of sediment accumulation caused by differential trap efficiencies and focusing effects in each sub basin of a multiple basin lake. 7) Lake basins are differentiated by physiography, both in terms of average specific sediment yield and dominant processes of sediment transfer, as indicated in the relation between drainage basin area and specific sediment yield (Figures 5.5 and 5.6). Highest sediment yields were observed in the North Coast Mountains where specific sediment yield increases with increasing drainage area. This trend is likely associated with the dominance of secondary remobilization of Quaternary sediments from stream banks and valley bottom areas (Church and Slaymaker, 1989). In the flat-lying plateau and major valley areas specific sediment yield decreases with increasing drainage area, thus fitting the conventional model of sediment delivery where storage efficiency increases downstream. In the Hazelton and Skeena Mountains there is no significant relation between specific yield and drainage 89 area. These results suggest that no single sediment yield model is adequate in describing the sediment transfer processes in British Columbia at the sub-regional scale. 8) Superimposed on all of the observed natural variability are some qualitative and semi-quantitative land use effects on sediment yield (Figures 4.9, 4.12, and 4.15). Land use impacts could only be partially separated from natural fluctuations, however, a clear land use signature, in the form of increased sedimentation rates, was observed in some of the study lakes (Figure 5.9). Largest increases have occurred in heavily harvested and roaded lake catchments in the Nechako Plateau and the Nass Basin and Major Valley regions. Significant increases were observed in basins that were subject to multiple land use disturbances. The greatest increase in sediment accumulation rates was observed in the Takysie Lake, where sedimentation rates increased an unprecedented 800% above background levels during human settlement activities (forestry, agriculture, grazing, residential construction, and resort/camping development) over the last century. 9) Lake sediment-based research can be an effective and useful approach to assess the long term impacts of forest harvesting and other land use disturbances on lacustrine sedimentation. There were, however, some limitations inherent in the methodologies used in this study. Suggestions for improving this study and overcoming some its limitations are included in the recommendations for future work section below. 6.2 Recommendations for Future Work There are many ways in which this current research on lake sedimentation in Northwestern British Columbia could be improved and further expanded. Based on the study results and from the experience of completing this project, the following recommendations have been compiled for future work: 1) All of the catchment information in this study was based on remotely sensed sources, primarily aerial photographs. It would be useful to expand the field component in similar projects to conclusively determine, and perhaps quantify, the sources, transport capacity, intermediate storage sites, and lake storage efficiency in the lake catchment sedimentary system. This would be beneficial in establishing underlying physical processes and cause-and-effect relations between catchment conditions and lake sediment signatures. 2) Only the laboratory analysis required to develop sediment accumulation rate profiles using 210Pb dating was done on the entire lake sample set. Additional analyses could be used to differentiate between the allochtonous and autochtonous sediment, such as loss on ignition (done on a few lakes in 90 this study) and biogenic silica content. It could also be useful to consider and test for non-catchment derived sources, which can also be a significant component of the lake sediment (Owens 1988). This would help distinguish between sediment derived from catchment erosion, within lake productivity, and other sources. There may also be more sensitive sediment parameters to land use impacts. Arnaud (1997) determined that change in organic content was the best indicator of forestry impacts on the west coast of Vancouver Island. 3) There would be many advantages in expanding this project to a multi-core study format for a sub-set of lakes. A single core approach was used because the large number of lakes included in the study would have made a multiple core approach impractical because of the much higher associated costs and time requirements. A multiple core study would enable a better assessment of within lake spatial variability, which is important in lakes with more complex morphometries. Errors associated with the 210Pb dating and other measurements could be described if replicate cores were available. A major advantage with the multiple core approach is that absolute sediment yields could be estimated to a much higher degree of accuracy. Absolute sediment yield estimates could be used with quantified measurements of sediment sources and intermediate storages (see first recommendation) to construct a complete sediment budget for a lake catchment. 4) It would be useful to establish longer sedimentary records for the study lakes. Additional dating techniques would be required, such as radiometric dating with l 4 C, improved varve counting procedures, or the use of dated event horizons (e.g. tephra layers from volcanic eruptions). Longer term records could be used to determine the importance of reoccurring, low frequency natural disturbances in sediment delivery to lake basins. Long term trends, possibly associated with climate change, in sedimentation, could also be better established. 5) Different procedures could be applied to increase the temporal resolution of the sediment profiles. The techniques used in this study can only resolve sediment accumulation data to periods of about 5 to 10 years. There are other coring methods, especially the freezing technique, that can preserve fine structures in the sediment (Saarnisto 1986). Also, if the sub-sampling of the sediment cores was done in the laboratory, smaller intervals could likely be extracted. More detailed profiles could then be constructed, which would better represent changing sedimentation patterns and allow analysis of the response and recovery curves in the sedimentation rate profiles. 6) The study could be expanded to investigate other land use impacts on lacustrine sedimentation. The focus on this study was on forestry related impacts on sediment yield. There were two basins in the study that also were subjected to additional land uses, including mining, grazing, agriculture, recreational activities, and residential development. Both of the receiving lakes showed major 91 increases in sediment yield coinciding with these activities. More work on these other land use disturbances would be clearly beneficial, since multiple land use activities often coexist in catchment areas. 7) The study could also be expanded to include a greater range of spatial scales and physiographic regions. Study results indicated that the drainage basin area/specific sediment yield relationship is variable in the different physiographic regions in Northwestern British Columbia. This relation is linked to downstream storage effects and remobilization of Quaternary sediment deposits, and holds major implications on geomorphological theory and for studies on land use effects on the sedimentary system. It would be useful to expand the study data set so that the specific sediment yield models for the province could be further refined. 8) A more careful examination of climate records could be useful in determining the cause of some of the temporal variability in the sedimentary records. For example, do periods of lower than average precipitation (e.g. Smithers 1965-1987, as shown in Figure 5.8) coincide with periods of reduced sediment yield? Shorter-term meteorological records available in the region could also be incorporated into the analysis (e.g. Masset, Alice Arm, Tlell, Anyox). 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Proceedings of a Symposium on Forest Land Use on Erosion and Slope Stability: 84, 7-11 May, Honolulu, Hawaii. Scrivener J.C., P.J. Tschaplinski, and J.S. MacDonald. 1998. An introduction to the ecological complexity of salmonid life history strategies and of forest harvesting impacts in coastal British Columbia. In Carnation Creek and Queen Charlotte Islands Fish/Forestry Workshop: Applying 20 Years of Coastal Research to Management Solutions. Hogan D.L., P.J. Tschaplinsld, and S. Chatwin (editors). B.C. Min. For., Res. Br., Victoria Sheridan W.L. and W.J. McNeil. 1968. Some effects of logging on two salmon streams in Alaska. J. Forestry, 66: 128-133. Short D.A. 1987. Response of northern California drainage basin to land use disturbance. In Erosion and sedimentation in the Pacific Rim. R.L. Beschta, T. Blinn, G.E. Grant, F.J. Swanson, and G.G. Ice (editors). IAHS Press, Institute of Hydrology, Wallingford, Oxfordshire, U.K. Stephenson, M., J. Klaverkamp, M. Motycka, C. Baron, and W. Schwartz. 1996. Coring artifacts and contaminant inventories in lake sediment. J. Paleolimnology, 15: 99-106. 101 Sullivan K. 1985. Long term patterns of water in a managed watershed in Oregon: 1. Suspended sediment. Water Resour. Bull. 21(6): 997-987. Swanson F.J. and CT. Dyrness. 1975. Impact of clear-cutting and road construction on soil erosion by landslides in the western Cascade Range, Oregon. Geology, 3: 393-396. Swanson F.J., M.M. Swanson, and C. Woods. 1981. Analysis of debris-avalanche erosion in steep forest lands: an example from Mapleton, Oregon, USA. In Proceedings of Erosion and Sediment Transport in Pacific Rim Steeplands Symposium: 81, January, The Royal Society of New Zealand, New Zealand Hydrological Society, IAHS, and the National Water and Soil Conservation Authority of New Zealand, pp. 67-75. Swanson F.J., L.E. Benda, S.H. Duncan, G.E. Grant, W.F. Megahan, L.M. Reid, and R.R. Zierner. 1987. 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A new method for the determination of flow directions and contributing areas in grid digital elevation models. Water Resour. Res. 33(2): 309-319. Tassone B.L. 1987. Sediment loads from 1973 to 1984: 08HB048 Carnation Creek at the mouth, British Colubmia. In Proceedings of the Workshop: Applying 15 years of Carnation Creek results. Chamberlin T.W. (editor). 13-15 January, Nanaimo, B.C. Trimble S.W. 1995. Catchment sediment budgets and change. In Changing River Channels. Gurnell A. and G. Petts (editors). John Wiley & Sons Ltd. 102 Vanoni, V.A. (editor). 1975. Sedimentation Engineering. Report in Engineering Practice No. 54, AMCE, New York. Weaver W.E., D.K. Hagans, and J.H. Popenoe. 1995. Magnitude and causes of gully erosion in the lower Redwood Creek Basin, northwestern Califronia. In Geomorphic Processes and Aquatic Habitat in the Redwood Creek Basin, Northwestern California. K.M. Nolan, H.M.Kelsey, and D.C. Marron (editors). U.S. Geological Survey Professional Paper 1454. 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IAHS Press, Institute of Hydrology, Wallingford, Oxfordshire, U.K. 103 Appendix A - Effects of Forestry on Sediment Transfer Literature review table: -All studies are from the Pacific Northwest, defined as the coastal mountain and intermountain areas of Northern California, Oregon, Washington, British Columbia and Southeast Alaska. -Codes used for study approach and scale (from Reid 1993): Approach: A - Reconstructs past using air photos or records D - Based on descriptive measurements E - Experimental S - Survey of multiple sites T - Long-term temporal monitoring study Scale: B - Paired basins or sites C - Case study M - Multiple basins or sites (sample size given) P - Process study s a u< cc •e =• a ?5 Q Q oo -5 a ' 2 13 . ;>> - Q t=) ^  c o ,.I s •a o S ej-us 4 - 1 13 I " O cn C O <L> u ss « 3 CA CA 13 S 2 o 2* .5 a, a; g E a. ° -E S 5 c o 00 =3 •a £ 8"-3 I •3 5 •a a CA s § § "a 6. S 3 E < is - T? •a O cd c .2 73 .5 •§ S ~. E „ 8 oo C cd y « .2 •o a , -T3 " u •8 00 X 3 Is, CA " O 2 "O g>8 •c § S J3 § s S B Q , CA O u CA eL, £ D S 3. o £ 5 o S u y E oo '•3 -E •£> <L> C " O cn a * JS 1 &0 -2 a w •c .5 cd (D - 2 > o 'C 5 -° O CD CA H £ S ?1 u u a a \'S o a o •a o E & 2 C W u. O g ca £ 73 o ? U U 73 U o. O U 00 I s 5c3 U o u T3 JS <*i 3 s H = § u (4 o u u u > a l l ° ^ CA ™ D 1> S CO ^ OH 5c3 j= -a B m 8 .5 .2 U s s • Z s o o , Z co O o e -° U 3 ai -o .2 ^ c C § I 1 Ja ^£ £ U c CJ ui ca ca E PQ ca 1 •o 'S CJ 00 ! 3 "§ E OX) S3 -° 5 •§ E o u I -> o <g s . 2 6 w-C/5 JO r-• 3 1 ed u ed c O O *2 i-i c . ed *t< - 3 £ =3 '« o +3 — >» O "8 b f l • -O - D , <U ea cj CJ co 7j -a C u , ' § 1 2 e I S3 '-3 ' CJ U I >%C/3 ' j5 B a. oo c OO Si § I I ed o 3 J= E C J g * •g. 00 •-£ c 2 S 3 . C C J •2 % CJ CJ C C J % ••= o u cn cn flj •O " •81 13 E "8 "2 e« o 52. a in 6 J3 o u u ' c u 2 c ej c o •c g-OS TI O 3 i a 6 1 1H E I < B s i x £ & 3 u • l l a £ o UJ CJ ,g 00 g-as "2 U .a o ' E fi a o 1°. 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CD 00 > ed CD Di oo s § 2 Di , S u O | Z < f2 col o •o Q •o OS U co IS | >» « ws > s S u «j a •o 5 «J <*H cn >-"S i ' « 23 " ot 5 a) S 2 11 .5 "S u S > , 0 , X ) .££ o S S S3 J .5 g 00 ~ O cS .5 3 * .S u o 3 2 S 3 -8 £•8 .3 S *- CA 1 5 a = . o ft • O CO J 3 " O 2 -o O i _ S * oo 0 . 2 "8 H -S to U ^2 •a > 5 ^ I J £ J 3 W IP 11 •« £ 2 = 73 =3 u « , o cd X ) T 3 S w ? r 2 11 H to ° U r -Cd 2 3 g §"8 •s oo-a — 1 3 -o S ? S e = a •S J= 1 E on < s a o § a u | B 3 > u .S" B U <D C o ot; z '£ -8 .5 S S C 14 « o i - o £ u z l a IE | , o i c S g I O . S S3 u £ u S3 109 Appendix B - Landscape Indices for Study Lakes Landscape variables extracted from the GIS database are included in this section. Study lakes are divided into the five defined physiographic regions for the study area: North Coast Lakes Page 110 Hazelton Mountain Lakes Page 111 Skeena Mountain Lakes Page 112 Nass Basin and Major Valley Lakes Page 113 Nechako Plateau Lakes Page 114 no Landscape Indices for North Coast Lakes Lake Name Drainage Basin Area (km2) Area of Study Lake (km2) Depth of Study Lake (m) Area of Lakes Upstream (km2) Wetland Area (km2) Valley Flat Area (km2) Drainage Density (km/km2) Mean Elevation (m) Mean Slope (degrees) Amoth 84.6 2.16 18 0.2976 1.6672 0.526 3.03 1019 31.2 Dragon 17.4 2.28 9 0.0011 0.0306 0.2895 1.58 645 16.1 Jade 33.6 1.4 42 0.2974 0.3125 0.0175 2.99 1202 20.8 Khtada 124 7.24 160 0.1263 0.3709 0.0038 2.12 790 31.8 Kwinamuck 40.3 1.83 5 0.1601 1.5579 0.0319 1.60 670 18.5 Minerva 3.2 1.38 72 0.0178 0 0 1.39 274 14.9 Toon 33 1.49 70 0 0.0107 0.0019 2.53 755 29.7 Tyke 13.2 2.34 90 0.2498 0 0 1.75 460 25.9 William 3.9 0.22 16 0.0346 0.041 0.0018 1.09 877 12.2 Landscape Parameters for Hazelton Mountain Lakes Lake Name Drainage Basin Area (km2) Area of Study Lake (km2) Depth of Study Lake(m) Area of Lakes Upstream (km2) Wetland Area (km2) Valley Flat Area (km2) Drainage Density (km/km2) Mean Elevation (m) Mean Slope (degrees) Aldrich 25.9 0.82 5.5 0.0621 1.5699 0.1785 1.49 1146 13 Chisholm 28 1.27 20 0.0317 0.2112 0.0265 1.58 1008 8.6 Collins 22 2.8 20 0.0092 0.106 0.043 0.83 927 7.8 Dennis 64.9 0.89 6 0.1023 1.3627 0.2289 2.21 1297 18 Douse 4.6 1.29 45 0.0743 0.1098 0 2.16 1211 9.9 Gordeau A 7.9 0.6 18 0.7571 0.4389 0.0356 2.58 1067 7.9 Gordeau B 3.7 0.46 21 0.0274 0.0694 0.0057 1.99 1083 10.8 Jackmould 6.5 0.27 9 0.0521 0.3884 0.0219 2.45 730 7.4 Louise 14.7 0.54 15 0.2396 0.7165 0.0193 2.19 1077 10.4 Mcbride 73.9 7.89 26 0.7338 0.8919 0.1085 1.03 904 5.9 Mcdonell A 11.7 1.32 18.5 0.0062 0.1119 0.0102 1.79 1013 11.3 Mcdonell B 131.3 0.93 20 0.339 2.2153 0.4452 2.09 1207 15.8 Newcombe 73.8 5.27 11 0.4473 4.2986 0.3926 2.99 1110 8.3 Sandstone 9.3 0.67 22 0.0425 0.8243 0.0438 1.63 1058 7.3 Shea 38.9 0.97 17 0.6807 1.3769 0.0266 2.53 1068 12 W.J. Holland 5.4 0.53 18 0.3881 0.1432 0.0073 0.74 909 7.8 112 Landscape Indices for Skeena Mountain Lakes Lake Name Drainage Basin Area (km2) Area of Study Lake (km2) Depth of Study Lake(m) Area of Lakes Upstream (km2) Wetland Area (km2) Valley Flat Area (km2) Drainage Density (km/km2) Mean Elevation (m) Mean Slope (degrees) Alpha 1.9 0.46 36 0 0.056 0.0123 2.35 1041 7.9 Beta 1.1 0.35 11 0.0541 0.1098 0.0095 1.84 1159 4.9 Camp 4.6 0.34 15 0.0017 0.1682 0.0135 1.2 879 6.4 Damsumlo A 6.5 0.42 14.5 0.025 1.0578 0 3.83 985 6 Damsumlo B 25.7 0.71 10 0.1685 1.6823 0 3.06 1246 10.7 Farewell 6.8 0.57 8 0.078 0.2357 0.0129 1.5 1056 11.8 Lake 21 A 1.7 0.3 5 0.0561 0.0145 0.0057 1.38 1019 4.8 Lake 21 B 4.3 0.17 5 0.0335 0.118 0.011 1.58 1046 9.1 Loneisland 5 0.45 14 0 0.1185 0.0255 2.41 955 4.5 Smokee 2.1 0.35 17 0 0.0752 0 1.95 901 8.9 Twin 20.8 0.35 5.5 0.2399 0.8568 0.0625 2.44 1005 9.4 Unnamed 1 4.9 0.75 27 0.1115 0.0355 0.0273 2.14 1420 7.4 113 Landscape Indices for Nass Basin and Major Valley Lakes Lake Name Drainage Basin Area (km2) Area of Study Lake (km2) Depth of Study Lake (m) Area of Lakes Upstream (km2) Wetland Area (km2) Valley Flat Area (km2) Drainage Density (km/km2) Mean Elevation (m) Mean Slope (degrees) Arbour 9.7 1.07 29 0.1074 0.0533 0.2096 2.22 799 9.9 Arrowhead 1.5 0.27 31.5 0 0 0 0.28 498 15.6 Bigfish 2.7 0.21 8 0 0.0344 0.0041 0.81 437 7.9 Derrick 27.4 0.59 14.5 0.1851 0.114 0.0274 1.81 722 11.7 Duckwing 1.4 0.46 34 0.006 0.026 0 0.5 581 6.4 Elizabeth 21.8 0.46 11.5 0.562 1.483 0.0639 2 415 3.9 Flatfish 2.2 0.29 8.5 0.0104 0.0459 0.0028 1.27 598 11.5 Hoodoo 6.8 0.52 16 0.0856 0.0272 0.0192 0.84 488 7.4 Kwinageese W 1 0.39 30 0 0 0.0036 1.56 672 9.6 Lakel3 9.8 0.36 21 0.1019 0.1699 0.0073 2.53 783 12.1 Lake4 4 0.44 19 0.04 0.0162 0.0051 1.85 596 7.9 Mitten 4.6 0.51 10 0 0.082 0.0008 1.34 630 14.4 Niska East 8.5 1.55 31 0.0035 0.0823 0.0023 2.07 707 12.7 Octopus 7.6 0.27 38 0.0005 0.046 0.0248 2.28 803 10.3 Paw 5.5 0.6 13.5 0.0105 0.008 0.0364 1.76 429 9.2 Pentz 1.6 0.27 24 0.0844 0.0949 0.0045 0.32 336 5.4 Sandal 0.9 0.26 5 0 0.0115 0 0 316 11.5 Unnamed KM1 14.8 0.68 21 0.26 0.4493 0.0411 2.94 456 10.6 Landscape Indices for Nechako Plateau Lakes Lake Name Drainage Basin Area (km2) Area of Study Lake (km2) Depth of Study Lake (m) Area of Lakes Upstream (km2) Wetland Area (km2) Valley Flat Area (km2) Drainage Density (km/km2) Mean Elevation (m) Mean Slope (degrees) Binta A 13.3 1.87 27.5 0.0641 0.179 0.0604 1.04 925 3.4 Binta B 136.4 6.51 39.5 1.8194 2.8447 3.6942 1.33 989 4.8 Bittern 3.1 0.62 4 0 0.0905 0.0217 0.45 889 5.7 Boomerang 7.6 0.54 6 0.1271 0.0573 0.0347 1.61 963 6.1 Boucher 2.7 0.36 6 0.0784 0.7173 0.0467 1.04 842 1.6 Bristol 33.6 0.85 5 0.2371 1.7171 0.1726 1.22 868 3.3 Clota 10.5 0.57 11 0 1.2945 0.0252 1.01 829 2.9 Doris 47 1.06 13 0.0277 0.8634 0.1579 1.62 1009 6.2 Haney 6 1.07 22 0 0 0.013 1.8 947 7.8 Horseshoe 19.9 2.09 13 0.0185 1.1231 0.0896 2.47 1001 4.5 Lake 10 2.7 0.64 22 0.1227 0.1993 0.013 1.05 1232 6.4 Lake 31 3.9 0.83 11 0.2301 0.2127 0.025 1.4 934 4 Lake 8 14.8 1.7 28 0.3515 0.2306 0.0151 2.5 635 10 LakeZ 43.5 1.15 10 0.2727 2.8001 0.3515 1.29 1091 7.1 Ligitiyuz 10 1.01 13 0 0.0762 0.046 1.04 1049 5.1 Parrot 94.1 3.69 35 0.9477 1.8503 0.2017 1.14 1033 9.3 Pinetree 5.7 0.51 8 0 0.1821 0.0184 2.68 996 6.8 Takysie 185.6 5.15 8 4.4853 8.5594 0.6771 1.17 928 4.7 Tanglechain A 5.6 0.69 7 0 0.0124 0.0706 1.44 915 4.3 Tanglechain B 0.6 0.3 7 0 0 0.0228 0.68 889 2.8 Torkelsen 18.3 1.51 7.5 0.4802 0.8113 0.0946 1.43 909 5.4 115 Appendix C - Land Use Summaries for Study Lakes Summaries of the land use variables extracted from the GIS database are included in this section. A complete listing can not be included because of the quantity of the data (variables were calculated on a yearly basis for each lake). Summaries include parameters describing overall land use disturbance for the lake catchments. Additional notes are also included for lakes with multiple land use disturbances. Study lakes are divided into the five defined physiographic regions for the study area: North Coast Lakes Page 116 Page 117 Page 118 Page 119 Page 120 Hazelton Mountain Lakes Skeena Mountain Lakes Nass Basin and Major Valley Lakes Nechako Plateau Lakes Land Use Summaries for North Coast Lakes Lake Earliest Year of Latest Year of Land Use Road Number of Area Logged Name Land Use Land Use Period Density Stream (%) (19xx) (19xx) (years) (km/km2) Crossings Dragon 58 97 40 0.9 7 33% Kwinamuck 86 97 12 0.6 13 12% Minerva 77 87 11 0.2 2 8.7% Tyke1 91 97 7 0.07 0 6.3% William 69 79 11 0.6 0 0.2% 1 includes helicopter logging of lake shoreline Land Use Summaries for Hazelton Mountain Lakes Lake Name Earliest Year of Land Use (19xx) Latest Year of Land Use (19xx) Land Use Period (years) Road Density (km/km2) Number of Stream Crossings Area Logged (%) Aldrich1 23 94 72 0.99 14 7.6% Chisholm 92 95 4 0.73 13 8.9% Collins 58 95 38 1.45 17 42.2% Dennis 23 94 72 0.64 40 8.6% Gordeau A 87 93 7 0.36 5 3.4% Gordeau B 87 93 7 0.76 2 . 10.5% Jackmould 73 89 17 1.93 14 33.3% Louise2 68 94 27 0.7 18 5.9% Mcbride 59 97 39 1.18 48 41.9% Mcdonell A 23 94 72 0.54 98 8.1% Mcdonell B 23 94 72 0.54 92 8.1% Newcombe 89 96 8 0.39 51 8.3% Sandstone3 91 95 5 0.35 2 6.2% W.J. Holland 87 96 10 0.01 0 2.4% 1 active mining from late 1920's to 1954, most productive in later years of mine operation 2 small scale mining operation active in the 1970's and 80's 3 21% of catchment burned in natural forest fire in approximately 1940 Land Use Summaries for Skeena Mountain Lakes Name Earliest Year of Latest Year of Land Use Road Density Number of Area Logged Land Use Land Use Period (km/km2) Stream (%) . (19xx) (19xx) (years) Crossings Camp 79 83 5 0.89 2 16.6% Twin 94 96 3 0.22 5 0.56% Land Use Summaries for Nass Basin and Major Valley Lakes Lake Name Earliest Year of Land Use (19xx) Latest Year of Land Use (19xx) Land Use Period (years) Road Density (km/km2) Number of Stream Crossings Area Logged (%) Arrowhead 78 93 16 0.24 0 6.2% Bigfish 79 89 11 3.85 3 59.2% Derrick 72 95 24 0.51 7 4.9% Duckwing 82 82 1 0.04 0 7.8% Elizabeth 65 93 29 1.23 13 34.4% Flatfish 90 96 7 1.51 3 19% Hoodoo 73 95 23 1.22 1 31.9% Mitten 67 96 30 0.98 4 30.7% Niska East 94 96 3 0.14 2 3.6% Octopus 78 92 15 0.36 4 0.2% Paw 92 94 3 0.4 1 6.6% Pentz 50 88 39 1.75 0 4.6% Sandal 81 92 12 0.67 0 7.5% Unnamed KM1 92 93 2 0.8 12 4.9% Land Use Summaries for Nechako Plateau Lakes Lake Name Earliest Year of Land Use (19xx) Latest Year of Land Use (19xx) Land Use Period (years) Road Density (km/km2) Number of Stream Crossings Area Logged (%) Binta A 51 96 46 0.99 115 23.5% Binta B 1 51 96 46 0.9 99 19.7% Bittern 80 85 6 0.68 1 6.1% Boomerang 60 89 30 1.0 21 12.5% Boucher1 94 94 1 0.2 0 4.9% Bristol 62 95 34 1.43 24 43.3% Clota 94 95 2 0.6 4 4.3% Doris 40 89 50 1.2 83 19.4% Haney2 81 81 1 0.41 1 0% Horseshoe 71 89 19 1.43 53 34.3% Lake 31 88 94 7 1.17 1 20.3% Lakez 92 95 4 0.21 2 2.8% Ligitiyuz 59 90 32 0.12 2 0.2% Parrot1 60 95 36 1.2 69 32.9% Pinetree 60 86 27 0.99 9 19.2% Takysie13 40 96 57 0.9 80 18.7% Tanglechain A 40 89 50 1.23 88 20.6% Tanglechain B 40 89 50 1.19 84 19.2% Torkelsen 63 95 33 0.88 12 12.4% 1 recent forest fire(s) in lake catchment 2 only minor trail developed 3 human settlement activities in lake catchment, including agriculture, grazing, and resort camping 121 Appendix D - Sedimentation Rates and Land Use History Sediment accumulation rates (SAR) of the study lakes are included in this section. Rates were calculated using the 210Pb dating procedures described in the methods chapter (Section 3.3). The dashed line indicates estimated background accumulation rates. Also provided are plots showing the timing and magnitude of timber harvesting and road construction. The number of new stream crossings accompanying road development is indicated above the road density bars. Additional notes are included to indicate the occurrence of other land use disturbances. Note when making lake to lake comparisons that the axes between lakes are not equivalent. Lakes are grouped according to physiographic region: North Coast Lakes Page 122 Page 124 Page 127 Page 129 Page 132 Hazelton Mountain Lakes Skeena Mountain Lakes Nass Basin and Major Valley Lakes Nechako Plateau Lakes North Coast Lakes 4000 3500 3000 2500 2000 SAR(g/m*/yr) AMOTH - background • 1910 19: 1970 1990 Road Denslly # of Stream Crossings % Logged 700, SAR(g/m2/yr) DRAGON background • Road Density # of Stream Crossings % Logged Jk. »»1 SAR(g/m2/yr) JADE •background • SARtg/nrWyr) KHTADA • background 1875 1895 1915 1935 Road Density # of Stream Crossings Road Density # of Stream Crossings 11 % Logged 1975 199.5 SAR(g/m*/yr) KWINAMUCK -background SAR(g/m2/yr) MINERVA -background 1BC0 1965 19TO 1S75 198S 1990 1995 Road Density # of Stream Crossings % Logged _n Q_ 19 1929 1939 1949 1959 1969 1379 1989 Road Density # of Stream Crossings % Logged North Coast Lakes SAR(g/m2/yr) TOON Road Density # of Stream Crossings % Logged background J » , SAR(g/m2/yr) WILLIAM • background tgi4 1934 Road Density # of Stream Crossings % Logged 1954 1974 SAR(g/m2/yr) TYKE - background 1885 1905 192S 1945 1965 19B5 Road Density # of Stream % Logged Hazelton Mountain Lakes SAR(g/m2/yr) ALDRICH •background Mining 18*7 1907 1927 1947 1987 1987 SAR(g/m2/yr) CHISHOLM Road Density # of Stream Crossings % Logged SAR(g/m2/yr) COLLINS TOO. SAR(g/m2/yr) -background • DENNIS •background Road Density # of Stream Crossings Road Density # of Stream Crossings •ru ITUlhrn-r % Logged % Logged A 0 '•"•I SAR(g/m2/yr) DOUSE Jl -background 1 SAR(g/m2/yr) GORDEAU BASIN A • background • 1856 1876 1896 1916 1956 1976 1872 1892 1912 1952 1972 1902 Road Density # of Stream Crossings % Logged Road Density # of Stream Crossings % Logged Hazelton Mountain Lakes SAR(g/m*/yr) GORDEAU BASIN B - background 1816 1836 1 856 1 876 Road Density # ot Stream Crossings 1916 1336 1956 % Logged SAR(g/m*/yr) JACKMOULD _ T ~ L '- background IMS 1668 1688 1908 1928 1948 1968 Road Density # of Stream Crossings % Logged SAR(g/m2/yr) LOUISE background Mining SAR(g/m2/yr) MCBRIDE background Road Density fl of Stream Crossings SAR(g/m*/yr) MCDONELL BASIN A - background SAR(g/m*/yr) MCDONELL BASIN B background Road Density # of Stream Crossings Un 1  n ID Road Density # of Stream Crossings i Logged % Logged Hazelton Mountain Lakes SAR(g/m2/yr) NEWCOMBE -background 1133 1153 1(73 1193 1913 1953 1973 1993 Road Density # ot Stream Crossings 12 ii % Logged SAR(g/nWyr) SANDSTONE • background forest fire ( 2 1 % of catchment) Road Density # of Stream Crossings % Logged SAR(g/m2/yr) SHEA background SAR(g/m2/yr) WJHOLLAND 1927 1937 1947 19S7 1907 1977 1987 1997 1133 1153 1B73 1993 1913 1933 1953 1973 1193 Road Density °* 1 tt of Stream Crossings % Logged Road Density # of Stream Crossings % Logged L Skeena Mountain Lakes SAR(g/m2/yr) ALPHA -background • 1712 1762 1812 Road Density # of Stream % Logged SAR(g/m2/yr) BETA J -background ts40 iaee 1SB6 1926 1946 1966 Road Density # of Stream Crossings % Logged SAR(g/m2/yr) CAMP background "i_r u1 SAR(g/m2/yr) DAMSUMLO BASIN A -background ^ 1 J l k 1608 1828 1848 1868 1888 1948 1966 1988 1950 1970 Road Density # of Stream Crossings Road Density # of Stream % Logged % Logged SAR(g/m2/yr) DAMSUMLO BASIN B —background SAR(g/m2/yr) FAREWELL background 194S 1958 Road Density # of Stream Crossings % Logged Skeena Mountain Lakes SAR(g/m2/yr) LAKE21 BASIN A •background • 1B21 1931 19*1 1951 1971 1981 1991 Road Density # ot Stream Crossings % Logged - i SAR(g/m2/yr) LAKE21 BASIN B •background 1837 1B57 1B77 1B97 1917 1937 1957 1977 1997 Road Density # ot Stream Crossings % Logged SAR(g/m2/yr) LONEISLAND —background 1879 1899 1919 1939 1959 1979 SAR(g/m2/yr) SMOKEE •background Road Density # ol Stream Crossings 1836 1858 1876 Road Density # ot Stream Crossings 1956 1976 % Logged % Logged IT SAR{g/m2/yr) TWIN -background "1_ SAR(g/m2/yr) UNNAMED1 •background 1942 1952 1972 1982 1843 1863 1883 1903 1923 1943 0.006 -I 0.004 . 0.002 Road Density # of Stream Crossings % Logged Road Density # of Stream Crossings % Logged Nass Basin and Major Valley Lakes SAR(g/m2/yr) ARBOUR 1 _r - background 1S47 11187 1887 1907 Road Density # ot Stream Crossings 1947 1967 % Logged SAR(g/m2/yr) ARROWHEAD 1672 1692 Road Density # of Stream Crossings % Logged -background 1972 1892 SAR(g/m2/yr) BIGFISH - background SAR(g/m2/yr) DERRICK •background 1872 1892 1932 1952 1972 1992 1915 1925 1945 1955 Road Density # of Stream Crossings % Logged % Logged 1975 1965 1935 Road Density # of Stream Crossings SAR(g/m2/yr) DUCKWING *>i SAR(g/m2/yr) ELIZABETH - background 1866 1886 190B 1926 1946 1966 1986 Road Density # of Stream Crossings % Logged background Nass Basin and Major Valley Lakes SAR(g/m2/yr) FLATFISH -background Road Density # of Stream a i J "Logged SAR(g/m2/yr) HOODOO •background • 1S4S 1866 1SSS 1906 1926 1946 1966 1966 Road Density # ol Stream Crossings % Logged j I • • SAR(g/m2/yr) KWINAGEESE •background 1029 1939 1949 19S9 SAR(g/m2/yr) LAKE13 -background Road Density # of Stream Crossin Road Density # of Stream Crossings % Logged % Logged SAR(g/m2/yr) LAKE4 • background SAR(g/m2/yr) MITTEN • background -1870 1890 1910 1830 Road Density #of Stream Crossings % Logged Road Density # of Stream Crossings % Logged Nass Basin and Major Valley Lakes SAR(g/m2/yr) NISKAEAST • background • 1835 1855 1875 Road Density # of Stream Crossings 1B15 1935 1955 1975 % Logged SAR(g/m2/yr) OCTOPUS •background Road Density # of Stream Crossings 0.002 0.0015 0.001 0 0005 % Logged SAR(g/m2/yr) PAW I SAR(g/m2/yr) PENTZ • background 1923 1933 1973 1983 1993 Road Density oj J # of Stream Crossings Road Density # of Stream Crossings % Logged % Logged SAR(g/m2/yr) SANDAL "L, -background 1 J SAR(g/m2/yr) UNNAMED KM1 - background 1843 1863 1683 1903 1923 1943 1963 1983 1B59 1879 Road Density # of Stream Crossings Road Density # of Stream Crossings % Logged % Logged Nechako Plateau Lakes SAR(g/m*/yr) BINTA BASIN A •background • 1908 1918 1926 Road Density # of Stream Crossings 1946 1956 1978 1968 % Logged JUL SAR(g/m*/yr) BINTA BASIN B background • ^ Forest fire {1% of catchment burned) Forest fire (29% of catchment burned) 1905 1915 1935 1945 1975 1965 Road Density # of Stream Crossings 0 3 1 % Logged JUk [UkinlljL SAR(g/m2/yr) SAR(g/m*/yr) BOOMERANG Road Density as \ it of Stream Crossings Road Density # of Stream Crossings % Logged w J % Logged SAR(g/m2/yr) BOUCHER - background Forest fire (8% of catchment burned) SAR(g/m2/yr) BRISTOL r •background 1953 1973 1857 1B77 1B17 1937 1977 1997 Road Density # of Stream Crossings Road Density # of Stream Crossings 0.04 0.02 % Logged % Logged i J J Nechako Plateau Lakes SAR(g/m2/yr) CLOTA -background -F 1642 1662 1B62 Road Density # ot Stream Crossings 1922 1942 % Logged SAR(g/m2/yr) HANEY J 1 background SAR(g/m2/yr) DORIS J Z Z I L background 1922 1942 1962 1982 Road Density # of Stream Crossings J U L % Logged I SAR(g/m2/yr) HORSESHOE 1910 1920 1940 1950 1970 1980 Road Density # of Stream Crossings Road Density # of Stream Crossings % Logged % Logged nil n SAR(g/m2/yr) LAKE10 r - background SAR(g/m2/yr) LAKE31 - background • 1»11 1931 1951 1971 Road Density # of Stream Crossings Road Density # of Stream Crossings % Logged Nechako Plateau Lakes , SAR(g/m2/yr) LAKE8 -background 1971 1991 Road Density # ot Stream Crossings 1 Logged SAR(g/m2/yr) LAKEZ J~~L -background IMS 1905 1925 1 945 1965 19S5 Road Density # of Stream Crossings ou % Logged SAR(g/m2/yr) LIGITIYUZ - background • SAR(g/m2/yr) PARROT D r - background Forest fire (over 50% of catchment burned) Road Density # of Stream Crossings 1B1S 1829 193S Road Density # of Stream Crossings 1856 1966 1976 JL % Logged % Logged JUL SAR(g/m2/yr) PINETREE TAKYSIE J -background 1859 1079 1919 1939 1959 1979 Road Density # of Stream Crossings 0 0002 0.0001 Road Density # of Stream Crossings JLiu % Logged % Logged Nechako Plateau Lakes SAR(g/m*/yr) TANGLECHAIN BASIN A •background Road Density # of Stream Crossings % Logged SAR(g/m*/yr) TORKELSEN -background 1651 1871 1931 1951 1971 I9S Road Density # of Stream Crossings % Logged SAR(g/m2/yr) TANGLECHAIN BASIN B IF -background 1S23 1933 1943 1953 1963 1973 19B3 Road Density # of Stream Crossings % Logged 136 Appendix E - Sedimentation Rate Statistics Lake Max. Min. Mean St.dev. Background Lake Max. Min. Mean St.dev. Background Aldrich 779 285 563 153 300 Lake 10 65 28 42 12 30 Alpha 92 49 63 14 52 Lake 13 174 94 118 23 98 Amoth 3718 1908 2499 544 2050 Lake 21 A 128 75 102 20 80 Arbour 162 59 101 34 62 Lake 21 B 137 57 90 25 62 Arrowhead 193 59 91 40 65 Lake 31 408 64 153 83 87 Beta 106 21 71 25 42 Lake 4 43 27 35 5 30 Bigfish 213 79 126 42 90 Lake 8 69 32 49 15 36 Binta A 285 107 202 54 130 Lake Z 326 154 218 49 175 Binta B 356 134 259 64 150 Ligitiyuz 172 107 124 17 120 Bittern 123 45 86 22 52 Loneisland 126 73 90 16 73 Boomerang 509 155 341 105 220 Louise 104 60 77 14 63 Boucher 547 175 374 94 280 Mcbride 390 104 175 82 115 Bristol 405 90 248 100 105 Mcdonell A 606 375 458 65 430 Camp 357 36 132 79 75 Mcdonell B 2699 403 1542 640 480 Chisholm 579 330 453 87 375 Minerva 157 34 63 35 39 Clota 236 68 121 48 78 Mitten 177 43 75 34 51 Collins 345 115 227 76 125 Newcombe 226 72 121 43 80 Damsumlo A 3071 307 1080 871 400 Niska East 122 36 74 27 35 Damsumlo B 2230 342 714 541 375 Octopus 310 24 122 88 52 Dennis 610 356 474 116 370 Parrot 306 88 139 62 90 Derrick 246 67 139 59 67 Paw 146 75 112 26 76 Doris 310 162 220 51 163 Pentz 86 27 56 23 32 Douse 1583 68 363 514 90 Pinetree 296 60 158 67 75 Dragon 585 345 450 73 360 Sandal 366 65 174 107 67 Duckwing 1257 83 451 400 95 Sandstone 109 57 71 17 60 Elizabeth 374 87 179 83 92 Shea 3670 165 877 969 320 Farewell 360 116 220 80 135 Smokee 70 37 48 12 40 Flatfish 158 36 103 46 39 Takysie 269 72 213 55 30 Gordeau A 171 44 99 41 44 Tanglechain A 579 127 236 112 140 Gordeau B 153 43 87 35 55 Tanglechain B 331 104 220 73 118 Haney 328 72 168 70 80 Toon 702 119 418 116 355 Hoodoo 105 73 88 13 77 Torkelsen 212 55 109 55 55 Horseshoe 172 50 107 34 54 Twin 1546 659 977 263 670 Jackmould 172 71 116 39 78 Tyke 183 104 141 24 120 Jade 1855 438 925 356 500 Unnamed 1 87 62 75 9 67 Khtada 1567 385 1022 305 390 Unnamed KM1 344 167 243 55 186 Kwinageese 45 15 24 9 16 William 111 51 80 20 49 Kwinamuck 698 387 590 88 350 Wjholland 178 38 69 38 40 1 3 7 Appendix F - Maps of Study Lakes Basic lake catchment maps showing the extent of road construction and timber harvest are included in this section. The maps were constructed by exporting and printing the base map layers from the GIS database (see methods chapter). All maps are orientated such that north is up when viewing the map upright. Double basin lakes contain two labeled sediment core locations. Lakes that comprise the cascading systems are also identified. Scale varies between catchment maps. Lakes are grouped according to physiographic region: North Coast Lakes Page 138 Hazelton Mountain Lakes Page 141 Skeena Mountain Lakes Page 145 Nass Basin and Major Valley Lakes Page 148 Nechako Plateau Lakes Page 153 The following legend is common for all maps: Catchment Boundary Lakes Rivers Wetland Roads | Cutblocks n Core Location 138 North Coast Lakes AMOTH 1000 0 1000 2000 Meters. DRAGON 1000 0 1000 2000 Meters JADE KHTADA 1000 0 1000 Meters 2000 0 2000 4000 Meters 139 North Coast Lakes KWINAMUCK 1000 0 1000 2000 3000 Meters MINERVA 300 0 300 600 Meters TOON 1000 0 1000 Meters TYKE 1000 0 1000 2000 Meters 140 North Coast Lakes WILLIAM [ / 250 0 250 500 Meters 141 Hazelton Mountain Lakes ALDRICH 750 0 750 1500 Meters CHISHOLM 750 0 750 1500 Meters COLLINS 1000 0 1000 2000 Meters DENNIS 2000 0 2000 Meters Aldrich Lake Outflow 142 Hazelton Mountain Lakes 143 Hazelton Mountain Lakes MCBRIDE 2000 0 2000 4000 Meters MCDONELL Dennis Lake Outflow 2000 0 2000 4000 Meters NEWCOMBE 1000 0 1000 2000 Meters SHEA 1000 0 1000 2000 Meters 1 4 4 Hazelton Mountain Lakes SANDSTONE 145 Skeena Mountain Lakes BINTA 146 Skeena Mountain Lakes BOUCHER 200 0 200 400 Meters BRISTOL CLOTA DORIS 500 0 500 1000 1500 Meters 2000 0 2000 4000 Meters 147 Skeena Mountain Lakes HANEY 500 0 500 1000 Meters HORSESHOE 1000 0 1000 2000 Meters LAKE 10 LAKE 31 500 0 500 1000 Meters 148 Nass Basin and Major Valley Lakes LAKE 8 LAKE Z 149 Nass Basin and Major Valley Lakes PINETREE 500 0 500 Meters TANGLECHAIN Doris Lake Outflow 500 0 500 1000 1500 Meters TORKELSEN 1000 0 1000 Meters TAKYSIE see full page map on following page 150 Nass Basin and Major Valley Lakes 151 Nass Basin and Major Valley Lakes ARBOUR ARROWHEAD BIGFISH DERRICK 500 0 500 1000 Meters 1000 0 1000 2000 Meters 152 Nass Basin and Major Valley Lakes DUCKWING 250 0 250 500 750 Meters ELIZABETH FLATFISH HOODOO 500 0 500 1000 Meters 1500 Meters 153 Nechako Plateau Lakes KWINAGEESE W. 500 0 500 1000 Meters LAKE 13 1000 0 1000 2000 Meters LAKE 4 MITTEN 250 0 250 500 750 Meters 154 Nechako Plateau Lakes NISKA EAST OCTOPUS 500 0 500 10001500 Meters PAW PENTZ 500 0 500 Meters 250 0 250 500 Meters 156 Nechako Plateau Lakes ALPHA 250 0 250 500 Meters BETA DAMSUMLO 2000 0 2000 Meters FAREWELL 500 0 500 1000 Meters 157 Nechako Plateau Lakes CAMP 158 Nechako Plateau Lakes TWIN 159 Appendix G - Precipitation Data Total annual precipitation data derived from total daily precipitation records for Prince Rupert (1908 - 1997), Terrace (1912 - 1998), and Smithers (1942 - 1998). Data provided by Environment Canada. All data are in millimeters. Years that contained missing data have been removed. 160 Prince Rupert 1909 2864 1965 2218 1911 2627 1966 2849 1912 2302 1967 2820 1913 3215 1968 2480 1914 2667 1969 2443 1915 2807 1970 2220 1916 2402 1971 2491 1917 2373 1972 2494 1918 2378 1973 2546 1919 2201 1974 3058 1920 2148 1975 2293 1921 2194 1976 2734 1922 2258 1977 2261 1923 3356 1978 2470 1924 2653 1979 2430 1925 2317 1980 2746 1926 2395 1981 2632 1927 2209 1982 2303 1928 2054 1983 2325 1929 2092 1984 2733 1930 2170 1985 2351 1931 2577 1986 2630 1932 2992 1987 3080 1933 2713 1988 2563 1934 2545 1989 2477 1935 1841 1990 2665 1936 2273 1991 3282 1937 1834 1992 2879 1938 1919 1993 2168 1939 3022 1994 2983 1940 2360 1941 2400 1942 2133 1943 2340 1944 1847 1945 2322 1946 2644 1947 2706 1948 2564 1949 2763 1950 2131 1951 2017 1952 2263 1954 2464 1955 2387 1956 2496 1957 1934 1958 2475 1959 2733 1960 2565 1961 2641 1962 2468 1963 2397 1964 2828 Terrace 1913 1204 1971 1294 1915 877 1972 1409 1916 886 1973 1227 1917 1234 1974 1283 1918 1192 1975 1296 1920 836 1976 1397 1921 1085 1977 1197 1922 1002 1978 1294 1923 1327 1979 1212 1924 1107 1980 1390 1925 1203 1981 1168 1926 1377 1982 1031 1927 1020 1983 876 1928 1166 1984 1403 1929 1289 1985 1165 1930 1248 1986 1336 1931 1226 1987 1581 1932 1488 1988 1410 1933 1322 1989 1473 1934 1190 1990 1516 1935 1241 1991 1847 1936 1313 1992 1609 1937 1048 1993 1305 1938 882 1994 1557 1939 1760 1995 1071 1940 1258 1996 1223 1941 1391 1997 1270 1942 1194 1943 1035 1944 1025 1945 998 1946 1088 1947 1316 1948 1019 1949 1173 1950 1002 1951 767 1952 947 1954 1395 1956 1398 1957 1069 1958 1451 1959 1667 1960 1301 1961 1365 1962 1312 1963 1381 1964 1329 1965 1205 1966 1345 1967 1284 1968 1581 1969 1064 1970 1041 Smithers 1943 312 1944 544 1945 462 1946 522 1947 761 1948 472 1949 464 1950 344 1951 487 1952 507 1953 606 1954 492 1955 438 1956 626 1957 634 1958 496 1959 684 1960 503 1961 620 1962 580 1963 474 1964 593 1965 515 1966 587 1967 431 1968 549 1969 423 1970 343 1971 549 1972 640 1973 443 1974 504 1975 507 1976 542 1977 504 1978 485 1979 406 1980 519 1981 498 1982 443 1983 470 1984 533 1985 475 1986 489 1987 485 1988 544 1989 536 1990 529 1991 579 1992 519 1993 602 1994 560 1996 617 1997 602 

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