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Spatial and temporal variability of the stream water chemistry of an alpine/sub-alpine catchment in the… Laudon, Hjalmar 1995

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SPATIAL AND TEMPORAL VARIABILITY OF THE STREAM WATER CHEMISTRY OF AN ALPINE/SUB-ALPINE CATCHMENT, IN THE COAST MOUNTAINS OF BRITISH COLUMBIA '• by HJALMAR LAUDON B.Sc, Umea University, Sweden, 1992 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Geography) We accept t h i s thesis as conforming to p.e required standard THE UNIVERSITY OF BRITISH COLUMBIA August 1995 © Hjalmar Laudon, 1995 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 G . d C X j C CX^KJ The University of British Columbia Vancouver, Canada Date r \ uq - 2 ^ , ^ S DE-6 (2/88) ABSTRACT The focus of t h i s study i s the hydrochemical v a r i a b i l i t y of runoff events i n two nested a l p i n e / s u b - a l p i n e basins. More s p e c i f i c a l l y , the aim i s to l i n k hydrograph i n t e r p r e t a t i o n s to r e s u l t s of hydrochemistry during r a i n storms i n order -to understand b e t t e r short term hydrochemical f l u x e s and v a r i a b i l i t y i n s o l u t e sources. Hydrograph separation was undertaken by using four h y d r o l o g i c a l t r a c e r s ; e l e c t r i c a l c o n d u c t i v i t y , concentration of s i l i c a , and the s t a b l e environmental isotopes oxygen-18 and deuterium. The d i f f e r e n t methods p r e d i c t e d c o n s i s t e n t high pre-storm water c o n t r i b u t i o n f o r the lower s t a t i o n at peak flow (60%-90%) but l e s s c o n s i s t e n t r e s u l t s were found at the upper b a s i n o u t l e t (25%-90%). The chemical c h a r a c t e r i s t i c s of the stream water have been analyzed using three d i f f e r e n t approaches, namely; s t a t i s t i c a l , mass balance, and thermodynamic. Linear c o r r e l a t i o n was used to i n v e s t i g a t e the s t a t i s t i c a l a s s o c i a t i o n between discharge and the i n d i v i d u a l chemical species. The mass balance approach was used to c o r r e l a t e s t o i c h i o m e t r y of the bedrock mineralogy to d i s s o l v e d c o n s t i t u e n t s i n the stream water. F i n a l l y , a thermodynamic technique was used to evaluate to what extent the stream water could be represented as an e q u i l i b r i u m system and how t h i s changed over the course of the storm. The re s u l t s from these methods showed that the stream water v a r i a b i l i t y was caused almost e n t i r e l y by d i l u t i o n from r a i n water input. i i i TABLE OF CONTENTS Abstract . . . i i Table of Contents i v L i s t of Tables .' . .' . . . . v i L i s t of Figures v i i Acknowledgements - v i i i CHAPTER 1 - INTRODUCTION 1 1.1 BACKGROUND 1 1.2 CHEMICAL WEATHERING 1 1.3 SPATIAL VARIABILITY OF'HYDROCHEMISTRY 3 1.3.1 BASIN MORPHOLOGY 3 1.3.2 SOILS 5 1.3.3 VEGETATION 6 1.3.4 LITHOLOGY 7 1.3.5 CLIMATE . . . 8 1.4 TEMPORAL FLUCTUATIONS IN HYDROCHEMISTRY . . . . 9 1.5 SUMMARY 12 CHAPTER 2 - STUDY AREA 14 2.1 LOCATION 14 2 .2 CLIMATE 14 2.3 GEOLOGY 17 2.4 VEGETATION 17 2.5 SOILS 18 2.6 HYDROLOGY 19 2.7 PREVIOUS WORK 19 CHAPTER 3 - FIELD AND LABORATORY METHODS 21 3.1 STREAM WATER MEASUREMENTS 21 3.1.1 ELECTRICAL CONDUCTIVITY AND pH 21 3.1.2 STREAM WATER SAMPLES 22 3.2 PRECIPITATION MEASUREMENTS 24 3.2.1 PRECIPITATION SAMPLES 24 3 .3 MAPPING 2 5 CHAPTER 4 - HYDROLOGY 2 7 4.1 DISCHARGE AND ELECTRICAL CONDUCTIVITY 27 . 4.2 PRECIPITATION 27 4.3 RUNOFF RATIO 2 9 4 .4 SUMMARY 31 CHAPTER 5 - HYDROGRAPH SEPARATION 33 5.1 INTRODUCTION 3 3 5.2 SEPARATION MODELS 34 5.3 HYDROGRAPH SEPARATION USING STABLE ISOTOPES . . 35 iv 5.3.1 RESULTS 3 5 5.3.2 VALIDITY OF METHOD 36 5.4 HYDROGRAPH SEPARATION USING SILICA 41 5.4.1 RESULTS 43 5.4.2 VALIDITY OF METHOD 45 5.5 HYDROGRAPH SEPARATION USING ELECTRICAL CONDUCTIVITY 4 6 5.5.1 RESULTS 47 5.5.2 VALIDITY OF METHOD 48 5.6 EXTRAPOLATION OF HYDROGRAPH SEPARATION 4 9 5.7 SUMMARY 51 CHAPTER 6 - CHEMICAL CHARACTERISTICS 56 6.1 INTRODUCTION 5 6 6.2 MASS-BALANCE APPROACH 57 6.2.1 RESULTS . 58 6.2.2 VALIDITY OF APPROACH 62 6.3 STATISTICAL APPROACH 63 6.3.1 RESULTS 64 6.4 THERMODYNAMIC APPROACH 66 6.4.1 RESULTS 67 6.4.2 MODEL CALCULATIONS 68 6.4.2 DISCUSSION 70 6.5 SUMMARY 71 CHAPTER 7 - CONCLUSIONS AND IDEAS FOR FUTURE RESEARCH . . 73 REFERENCES CITED 77 Appendix I 87 Appendix II 88 Appendix III 89 Appendix IV 90 Appendix V 91 v LIST OF TABLES Table 2.1. Surface cover i n the study area 18 Table 4.1. Storm runoff r a t i o for p r e c i p i t a t i o n events. . 30 Table 5.1. Comparison between hydrological tracers using Friedman analysis of variance 50 Table 6.1. Assumed major minerals contributing to hydrochemistry. 58 Table 6.2. Mass-balance reactions 59 Table 6.3. Relative contribution of minerals to hydro-chemistry 61 Table 6.4. Correlation between discharge and i n d i v i d u a l solutes 65 v i LIST OF FIGURES Figure 2.1. Map of B r i t i s h Columbia showing study l o c a t i o n (upper panel) and b a s i n geology and b a s i n topography (lower) 15 Figure 2.2. Vegetation map (upper panel) and l o c a t i o n of monitoring s t a t i o n s and bulk p r e c i p i t a t i o n gauges (lower) 16 Figure 4.1. Discharge and e l e c t r i c a l c o n d u c t i v i t y f o r the e n t i r e f i e l d season at the two monitoring s t a t i o n s , and p r e c i p i t a t i o n at the lower s t a t i o n . . . . . . . 28 Figure 5.1. Hydrograph separation using n a t u r a l s t a b l e isotopes 37 Figure 5.2. Meteoric isotope l i n e f o r northern hemisphere 42 Figure 5.3. Hydrograph separation using e l e c t r i c a l c o n d u c t i v i t y , s i l i c a and s t a b l e isotopes 44 Figure 5.4a. Hydrograph separation of event #1 and #2 at the lower monitoring s t a t i o n using e l e c t r i c a l c o n d u c t i v i t y 52 Figure 5.4b. Hydrograph separation of event #4 and #5 at the lower monitoring s t a t i o n using e l e c t r i c a l c o n d u c t i v i t y 53 Figure 6.1. A c t i v i t i e s of stream water samples f o r the two monitoring s t a t i o n s p l o t t e d on a mineral s t a b i l i t y diagram 6 9 v i i ACKNOWLEDGEMENTS My s i n c e r e s t thanks to my supervisor Olav Slaymaker who provided the p e r f e c t balance of guidance and freedom f o r me to s u c c e s s f u l l y complete t h i s task. I genuinely enjoyed h i s unwavering encouragement and support. I thank Tom Brown, my second reader, f o r i n t r o d u c i n g me i n t o the world of chemical thermodynamics and i r r e v e r s i b l e mass t r a n s f e r . During t h i s study I have g r a t e f u l l y r e c e i v e d funding f o r f i e l d work from the Swedish So c i e t y of Anthropology and Geography, the Royal Swedish Academy of Science (Margit A l t i n s fond, H i e r t a R i t z e u s fond and Olof A h l o f s fond) and through funding to Dr. 0. Slaymaker by the Natural Sciences and Engineering Research C o u n c i l , Operating Grant 5 - 87073. My stay at UBC would not have been p o s s i b l e without, the f i n a n c i a l support from Sverige-Amerika s t i f t e l s e n , Ingenjorsvetenskapsakademin and CSN. I owe great a p p r e c i a t i o n to Wendy Hales f o r her tremendous help w i t h f i e l d work, f o r reviewing the many stages of my manuscript and f o r j u s t being a great f r i e n d . I want to thank Per Lundstrom f o r h i s help i n the f i e l d and Manon f o r her help w i t h the l i t t l e bushes. I a l s o thank Marcus, Fern, Jonathan, J i l l , Mum, Dad and S o f i a f o r v i s i t i n g one of the most b e a u t i f u l places on earth, and Marty and the l a t e A l S t a h l i f o r t h e i r great h o s p i t a l i t y and enjoyable d i s c u s s i o n s . I a l s o owe Bengt Cyren a great thanks f o r h i s help w i t h the l a t e s t i n micro e l e c t r o n i c s . I f u r t h e r extend my thanks to the whole Geography Department at U.B.C, e s p e c i a l l y the 500-group, f o r i n one way or another c o n t r i b u t i n g to an enjoyable l i f e during the s t r u g g l e . Without the s k i i n g , h i k i n g , car-break-downs, cinnamon buns, bears and beers, my stay would j u s t not have been what i t was. and I want to thank Asa f o r everything! v i i i CHAPTER 1 - INTRODUCTION 1.1 BACKGROUND Many alpine hydrochemical studies during the l a s t decade have been focused on the long term fluctuations of water qua l i t y . These studies are motivated by concerns about pote n t i a l impact of acid deposition on aquatic and t e r r e s t r i a l ecosystems (e.g. Drever and Hurcomb, 1986; Kattleman, 1989; and Baron, 1992). R e l a t i v e l y l i t t l e attention, however, has been devoted to short term hydrochemical fluxes of alpine stream water, which i s an important aspect of both a c i d i f i c a t i o n and transport of contaminants i n these areas. The focus of t h i s study i s , therefore, to investigate the hydrochemical v a r i a b i l i t y of two nested alpine/sub-alpine basins during d i s t i n c t hydrological events. In p a r t i c u l a r , the study objective i s to re l a t e the int e r p r e t a t i o n of hydrograph separation to hydrochemical analysis i n order to understand better short term hydrochemical fluxes and v a r i a b i l i t i e s i n solute sources. 1.2. CHEMICAL WEATHERING Chemical weathering reactions i n •bedrock and s o i l s are the primary source of solutes i n the hydrosphere. The most important weathering process of s i l i c a t e and aluminosilicate minerals i s known as hydrolysis. The hydrolysis reaction consumes protons and produces other solutes while transferring primary minerals to a secondary face. 1 The main sources of protons i n areas without anthropogenic influence on atmospheric composition are carbonic and organic acids. Oxidation of naturally occurring sulphide, eg. p y r i t e , can also contribute to the a c i d i t y and hence control the hydrochemistry of stream waters (Raiswell and Thomas, 1984; Basset et a l . 1992). The thermodynamic relationship of the minerals involved i n weathering reactions reveals what f i n a l water composition could be expected i n a closed hydrological system experiencing equilibrium (ie. Garrels and Christ, 1965). Chemical thermodynamics i s also valuable when i d e n t i f y i n g stable and unstable minerals at s p e c i f i e d pressure, temperature and a c t i v i t y of i n d i v i d u a l solutes (Bricker, 1972). Most surface waters are, however, open hydrological systems with a r e l a t i v e l y short residence time i n the subsurface environment, which prevents equilibrium or steady state conditions from being reached. Due to the reaction k i n e t i c s of the system, the highest rock d i s s o l u t i o n rate i s at the beginning of the encounter between water and. minerals' (eg. T r u d g i l l , 1986). Flushing of d i l u t e water through the hydrological reservoirs i n the landscape, therefore, enables the reaction to continue at a high rate, whereas i n a closed system the rock d i s s o l u t i o n w i l l decelerate as equilibrium i s approached. 2 1.3. SPATIAL VARIABILITY OF HYDROCHEMISTRY 1.3.1. BASIN MORPHOLOGY The importance of elevation on solute concentration of runoff was investigated by Drever and Zobrist (1992) by comparing the hydrochemistry of a series of small g r a n i t i c gneiss catchments at d i f f e r e n t elevations i n southern Switzerland. They found that the concentrations of .the major cations and s i l i c a i n surface waters decreased exponentially with higher elevations. Drever and Zobrist hypothesized that decreased concentration of i n d i v i d u a l species with higher elevation was the r e s u l t of thinner s o i l s , selective chemical weathering and a change i n s o i l clay mineralogy. The findings of Drever and Zobrist (1992), that stream and lake water at high elevations are d i l u t e corresponds well with other high a l t i t u d i n a l hydrochemical studies, such as those i n Sweden (Degerman et a l . 1992), Colorado (Mast, 1992), Sierra Nevada (Williams and Melack, 1991) and the B r i t i s h Columbia Coast Mountains (Gallie, 1983). Details of water movement through the landscape are of fundamental concern when interpreting the influence of basin c h a r a c t e r i s t i c s on runoff chemistry. The basin morphology controls the mixing of surface, subsurface and groundwater (Mcdonnell et a l . 1991) and therefore controls stream chemistry. In a study car r i e d out by Zecharias and Brutsaert (1988) both a n a l y t i c a l results and t h e i r interpretation showed that the 3 parameters which most strongly controlled outflow of groundwater were t o t a l length of perennial streams, average basin slope and drainage density. Increased geochemical load downstream i n stream channels has also been found i n several other studies (eg. Foster and Grieve, 1984; Calles, 1985). The enhanced solute concentration i n the downstream d i r e c t i o n i n these studies has been explained by increased groundwater outflow. Calles (1985) found that the portion of deep groundwater increased from 5% to 20% of the t o t a l flow, along a 500 meter reach i n the downstream d i r e c t i o n . Foster and Grieve (1984) also found a s i g n i f i c a n t downslope increase i n solute concentrations but discovered a large solute increase i n the subsurface throughflow towards the stream channel as well. Concavities, hollows and slope bases experience a concentration of subsurface throughflow and solute a c q u i s i t i o n . This has been found where the t r a v e l distance for throughflow i s small and the water s t i l l d i l u t e (Crabtree and Burt, 1983). At the slope base, however, t h i s i s often not the case as the water, before i t reaches the base of the slope, i s already enriched with solutes and has, therefore, less weathering potential (Burt, 1986) . Dixon (1986) found a large topographic influence on solute enrichment. He suggested that high topographic positions are areas of solute uptake, midslopes are areas of transport and removal, and base slopes are dominated by transport and accumulation. It has however been shown that the most rapid 4 solute enrichment occurs as soon as d i l u t e meltwater and p r e c i p i t a t i o n encounters sedimentary material (eg. Rainwater and Guy, 1961 and T r u d g i l l , 1986). Dixon's model i s , therefore, probably much too simplified, even though i t l a r g e l y follows the conclusions of Foster and Grieve (1984), who demonstrated that the geochemical load increased downstream i n both channel and subsurface throughflow. Variations i n streanibed topography can influence p o t e n t i a l energy d i s t r i b u t i o n at the streambed subsurface interface (Harvey and Bencala, 1993). Harvey and Bencala suggested that the pot e n t i a l energy v a r i a t i o n could exert a s i g n i f i c a n t control on surface-subsurface water mixing i n mountain streams. F i e l d evidence supported t h e i r hypothesis, e s p e c i a l l y where the slope di s c o n t i n u i t y and the spacing between stepped bed units i s large. The increased potential energy was found to have a s i g n i f i c a n t influence on solute transport by recharging water to subchannel flow paths. Return of solute enriched substream water occurred where stream channel slope decreased. 1.3.2. SOILS It has been found i n lowland areas that the chemical-hydrological i n t e r a c t i o n i n the near stream zone l a r g e l y controls the solute contribution to streams (e.g. Pionke et a l . 1988). Whether the near stream zone i s of si m i l a r importance i n 5 high mountain areas i s questionable due to steep topography and th i n s o i l s forcing water to bypass the s o i l matrix as i t flows downhill. In spite of the r e l a t i v e l y l i m i t e d d i s t r i b u t i o n of s o i l s i n mountainous catchments, t h e i r importance i n the near stream zone has been i d e n t i f i e d by Baron et a l . (1992) . They concluded that the largest r e l a t i v e influence on stream water chemistry i s caused by the fact that s o i l s i n most alpine regions are concentrated on the v a l l e y f l o o r s adjacent to the stream channel. The importance of s o i l s i n contributing solutes to streams i s found i n the hydrological c h a r a c t e r i s t i c s and pedochemical a c t i v i t y of the solum (Gallie and Slaymaker, 1984). S o i l s are extremely reactive due to t h e i r large s p e c i f i c surface area (Tan, 1'993), and ion adsorption and retention are rapid enough that they can exercise a disproportionate influence on surface water chemistry. 1.3.3. VEGETATION Although only a small percentage of most alpine and subalpine areas i s vegetated, forest and meadows can be important sources and sinks for nutrient and certain'non-nutrient ions (Arthur, 1992). Her conclusions conform well with those of T e t i (1979) who argues that biomass i n an alpine region i s important not only because of s p a t i a l d i s t r i b u t i o n but also because of the temporal v a r i a t i o n of ionic release. Foster and Grieve (1984) came to si m i l a r conclusions that the r e l a t i v e chemical composition of p r e c i p i t a t i o n chemistry i s not only a l t e r e d by 6 the biosphere, but that vegetation has a r e l a t i v e l y high impact on solute loading. Most geochemical weathering studies hypothesize steady state elemental cycl i n g of the vegetation (eg. Clayton, 1986). The q u a n t i f i c a t i o n of solute release from vegetation becomes important i n areas of anthropogenic influence (Paces, 1986), or sensitive alpine environments, which are forced out of steady state by climatic fluctuations. It i s also not l i k e l y that steady state conditions i n the vegetation can be achieved during individual hydrological events when flushing of accumulated material can be expected. The e f f e c t of C02 contribution from vegetation, and, hence, hydrogen production i s expected to increase the chemical weathering rates below the tree l i n e . The C02 p a r t i a l pressure encountered i n s o i l systems due to b i o l o g i c a l r e s p i r a t i o n often exceeds the concentration of the atmosphere by 100 times (Creasey et a l . 1986). 1.3.4. LITHOLOGY It i s apparent that the l i t h o l o g y has an important role i n c o n t r o l l i n g stream water chemistry. This has also been shown i n several mountain studies, by Reynolds and Johnson (1972) i n s i l i c a t e bedrock and by Basset et a l . (1992) i n sulphidic material. The geochemistry of the parent material determines the equilibrium concentration and reaction rates and, therefore, what elements could become available as weathering products. The bedrock geochemistry, however, i s not the sole indicator of chemical weathering rates. The rate of d i s s o c i a t i o n depends also 7 on an array of physical bedrock c h a r a c t e r i s t i c s . Eggelton (1986) found the structure of mineral complexes, cleavage planes and c r y s t a l shape to be of major importance for the s u s c e p t i b i l i t y to chemical weathering. D i f f e r e n t i a l chemical weathering i s also influenced by the heterogeneity of the rock mineralogy (Sparks, 1971) , and at j o i n t s , fractures and bedding planes (Clark and Small, 1982). More rapid mineral d i s s o l u t i o n i n the mentioned structures i s caused by larger exposed surface areas. 1.3.5. CLIMATE Climate could be considered the most important variable a f f e c t i n g chemical weathering rates due to i t s obvious control on the hydrological regime and vegetation. The single most important variable i n the context of chemical weathering i s the a v a i l a b i l i t y of water (Dethier, 1986). Thus, chemical weathering rates tend to be highest i n areas of high runoff. Often coinciding with high chemical weathering rates and high runoff volumes are, therefore, streams with very d i l u t e water due to short average residence time i n the subsurface environment. The temperature effect has been discussed by Colman and Dethier (1986) . They suggest that a raised temperature w i l l decrease the equilibrium concentration and hence the mineral s o l u b i l i t y but increase the rate of chemical weathering as both the d i s s o l u t i o n k i n e t i c s and thermodynamics of the system are affected. O i l i e r (1984) suggests that a 10° C r i s e i n temperature could double 8 the r a t e of chemical weathering. However, chemical weathering and removal of s o l u t e s were found to be an important denudation f a c t o r , by Rapp (1960) i n a s u b a r c t i c small b a s i n study and by C o l l i n s and Young (1981) i n g l a c i a l environments. Such s t u d i e s , c a r r i e d out i n c o l d environments, suggest that chemical weathering r e a c t i o n s are important not only i n t r o p i c a l and humid c l i m a t e s but i n p o l a r and a l p i n e regions as w e l l . 1.4. TEMPORAL FLUCTUATIONS IN HYDROCHEMISTRY The temporal v a r i a b i l i t y of surface water chemistry i s mainly c o n t r o l l e d by p a r t i t i o n i n g of water between surface and subsurface sources. Even though most high mountain areas have very d i l u t e runoff water, large temporal v a r i a t i o n s i n the runoff hydrochemistry occur. Large d i u r n a l f l u c t u a t i o n s of so l u t e s occur during snowmelt i n s p r i n g and during summers i n g l a c i e r i z e d , b a s i n s ( C o l l i n s , 1977, 1979) and during storm events (Kattleman, 1989). The importance of subsurface c o n t r i b u t i o n s i n a l p i n e areas to the runoff hydrochemistry depends, t h e r e f o r e , on the t i m i n g of inputs from d i l u t e snowmelt and stormflow, not from the t o t a l outflow of h i g h l y concentrated subsurface water. The v a r i a b i l i t y of the. geochemical load i s caused by the p a r t i t i o n i n g of water between surface, s o i l and groundwater sources. Large v a r i a b i l i t y i n water chemistry occurs between the base flow and the storm flow components. The base flow comprises water o r i g i n a t i n g mainly from the lower mineral horizons and 9 groundwater w i t h long residence time. The storm flow component i s produced during hydro l p g i c events when the base flow i s d i l u t e d by lar g e volumes, of p r e c i p i t a t i o n or meltwater. The p a r t i t i o n i n g of water pathways can vary both s e a s o n a l l y (Kattleman, 1989) and during i n d i v i d u a l storm events (Creasey et a l . 1986) . A l p i n e areas are c h a r a c t e r i z e d by r a p i d h y d r o l o g i c a l processes, caused by high' h y d r a u l i c gradients, high flow v e l o c i t i e s and f a s t t r a n s m i s s i o n of h y d r a u l i c impulses ( S i l a r , 1990) . The short residence time ' of water i n a l p i n e areas, r e s u l t i n g i n d i l u t e r u n o f f , does not n e c e s s a r i l y i n d i c a t e a lower p r o p o r t i o n of subsurface water compared w i t h that of lowland areas. However, i t does prevent chemical weathering r e a c t i o n s from proceeding towards steady s t a t e and e q u i l i b r i u m a c t i v i t i e s . The p r e c i s e h y d r o l o g i c a l pathway has important i m p l i c a t i o n s on residence time and hence on so l u t e enrichment. I d e n t i f i c a t i o n of the water pathway gives an understanding of magnitude and t i m i n g of s o l u t e f l u x e s from d i f f e r e n t h y d r o l o g i c a l r e s e r v o i r s i n the landscape (Slaymaker, 1988) and i s , t h e r e f o r e , e s s e n t i a l f o r the understanding of v a r i a t i o n s of the streamwater chemistry. Many hydrograph separation stud i e s have been c a r r i e d out i n lowland areas during the l a s t decades. Discrepancies between r e s u l t s from stream-oriented chemical and n a t u r a l isotope s e p a r a t i o n of storm runoff i n t o sources of storm and pre-storm water o f t e n 10 appear to contradict results from hillslope-based (hydrometric) studies. This has been the si t u a t i o n i n the • steep humid catchment, Maimai, on the South Island of New Zealand. Hydrometric studies by Mosley (1979, 1982), using a r t i f i c i a l tracer monitoring and subsurface flow measurements to investigate the catchment's fast response to p r e c i p i t a t i o n inputs, suggested that storm flow was controlled by rapid runoff of storm water routed through macropores. Work by Pearce et a l . (1986) and Sklash et a l . (1986), employing natural stable isotopes and chemical tracers, e x p l i c i t l y refuted Mosley's in t e r p r e t a t i o n by demonstrating that the storm hydrograph volumetrically was dominated by pre-storm water during high-frequency storms. Implicit i n t h e i r argument i s that the large pre-storm water component i s generated by near stream saturated overland flow and that macropore flow or other rapid-flux mechanisms could not explain the fast contribution of water to the stream. More recent findings, however, by McDonnell (1990), and McDonnell et a l . (1991) showed that a large pre-storm water f r a c t i o n (up to 95% of t o t a l runoff) i s routed through preferred macropore pathways. The problems encountered at the Maimai catchment could have important implications for many former hydrograph separations. This i s true for mountain areas, i n pa r t i c u l a r , where rapid hydrological response together with low solute concentrations could be used as misleading evidence for overland flow or 11 macropore flow contributing event water as the main component to the storm hydrograph. Unfortunately, ho previous studies using hydrograph separation methods i n alpine areas to analyze the proportion of event and pre-event water during storm flow were available to the author. 1.5 SUMMARY Surface water hydrochemistry i s the end product of i n t e r a c t i n g biogeochemical processes i n the drainage basin. Chemical weathering processes are the main solute contributors to runoff i n areas of li m i t e d anthropogenic influence. However, cation exchange reactions i n s o i l s , and leaching of organic material, can form variable sources and sinks of in d i v i d u a l chemical species. G a l l i e (1983) has concluded that the hydrochemistry of runoff i s a function of: i) The number and type of hydrologic reservoirs i n the landscape; i i ) The net chemical., r e a c t i v i t y of each hydrologic reservoir; and, i i i ) The volume flux rate of water within each hydrologic reservoir. Consequently, stream water chemistry i s a function of the mean residence time of the water and the chemical r e a c t i v i t y of each reservoir. Reservoir contributions to the flux and magnitude of 12 solutes, therefore, can be evaluated by studying sources and sinks of solutes i n the system and p r i n c i p a l pathways of water i n the catchment. 13 CHAPTER 2 - STUDY AREA 2.1 LOCATION The study s i t e comprises a west-facing catchment, straddling the alpine-subalpine ecotone i n the P a c i f i c Ranges of the Coast Mountains, about 120 km north of Vancouver, B r i t i s h Columbia (figure 2.1). The 0.36 km2 watershed i s situated 1525 to 1950 meters (5000-6400 feet) above sea l e v e l . The catchment i s divided into two sub-basins: upper and lower basin, with areas of 0.29 km2 and 0.07 km2 respectively (figure 2.1). The study basin has a marked v a l l e y asymmetry with a steep, 25-40° north-facing talus slope and with more gentle, 5-15° vegetated south-and west-facing slopes. 2.2 CLIMATE The meso-scale climate i n the study area i s cold, perhumid. The P a c i f i c Ranges are oceanic and therefore receive large amounts of winter p r e c i p i t a t i o n , making up more than 70% of t o t a l p r e c i p i t a t i o n (Gallie, 1983). The cold, oceanic climate maintains alpine g l a c i e r s i n the area with l o c a l g l a c i a l equilibrium l i n e a l t i t u d e -fluctuating around 2100 m.a.s.l. Individual years have experienced twelve months of snow cover i n the upper basin but the winter snowcover does not usually p e r s i s t beyond September (Slaymaker, personal communication, 1993) . 14 F i g u r e 2.1. Map o f B r i t i s h Columbia showing s t u d y l o c a t i o n (upper panel) and b a s i n g e o l o g y and b a s i n t o p o g r a p h y ( l o w e r ) . 15 1:7500 0 100m Figure 2.2. Vegetation map (upper panel) and l o c a t i o n of monitoring stations and bulk p r e c i p i t a t i o n gauges (lower). 16 2.3 GEOLOGY Regional bedrock geology c o n s i s t s of Coast Mountains Complex quartz d i o r i t e , which i s o v e r l a i n by a roof pendant of Cretaceous Gambier Group metasediments on the south r i d g e (Journeay, i n press) ( f i g u r e 1). A d e t a i l e d geochemical survey was c a r r i e d out by G a l l i e (1983) i n the upper most part of the study area, Goat Meadows. He suggested that the mineralogy of the quartz d i o r i t e complex c o n s i s t s of; quartz 30%, p l a g i o c l a s e (An 40) 20%, K-feldspar 15%, hornblende 10% w i t h a number of accessory minerals, and the metasediments of quartz 60%, a c t i n o l i t e 21%, c h l o r i t e 13% and accessory minerals. G a l l i e (1983) a l s o found dyke swarms of v e s i c u l a r b a s a l t and t r a c e s of a f e l d s p a r porphyry. P y r i t e i n small amounts was found to be u b i q u i t o u s i n the study basin. V i s i b l e bedrock outcrops i n the study area are h e a v i l y f r a c t u r e d . Fractures range i n s i z e from microscale features to s e v e r a l meters deep, and hundreds of meters long. The l a r g e r f r a c t u r e s , evident on the southern d i v i d e of the b a s i n , are i n t e r p r e t e d . as t o p p l i n g features (Slaymaker, personal communication, 1 9 9 5 ) . . . . 2.4 VEGETATION South- and west-facing slopes range i n surface cover from a l p i n e f i r (Abies l a s i o c a r p a ) and mountain hemlock (Tsuga mertensiana) w i t h understory of predominantly heather (notably, Cassiope 17 mertensiana and Phyllodoce g l a n d u l i f l o r a ) and rhododendron (Rhododendron a l b i f l o r u m ) to sedge ( i e . Carex n i g r i c a n s and Carex s p e c t a b i l i s ) , moss ( i e . lycopodium sp. ) , l i c h e n s ( i e . Cladonia sp.) and bare s o i l (see t a b l e 2.1) . The steep north-f a c i n g v a l l e y - s i d e c o n s i s t s predominantly of unvegetated t a l u s slopes and rock b l u f f s ( f i g u r e 2.2). Table 2.1. Surface cover i n the study area. Surface"cover Upper bas i n Lower b a s i n Bedrock and t a l u s 48% 48% Stands of c o n i f e r s 13% 37% Heather, l i c h e n s and moss 29% 12% Grassy-sedge meadow 2% 2% Bare s o i l 7% <1% Ponds 1% <1% 2.5 SOILS In the upper basin, s o i l s have been described according to the Canadian system of c l a s s i f i c a t i o n (Canadian S o i l Survey Committee, 1978) by G a l l i e (1983) and Souch (1984) . In t r e e stands s o i l s are O r t h i c Humo-Ferric Podzols. In grass and heather areas s o i l s are dominated by O r t h i c D y s t r i c and O r t h i c Sombric B r u n i s o l s and Cumulic Regosols. Owens (1990) suggests that s o i l s i n the Lower Basin, i n general, are s i m i l a r to s o i l s d e s cribed by G a l l i e (1983) and Souch (1984) . B a r r e t t (1981) and B a r r e t t and Slaymaker (1989) found hydrophobicity i n many of the s o i l s i n the study area. 18 2.6 HYDROLOGY The outlet of a small oligotrophia pond, Middle Lake, defines the boundary between the two study basins. The elevation of Middle Lake i s approximately 1680 meter above sea l e v e l . The lake i s fed by one main stream flowing primarily at the contact between the talus slope and slopes vegetated by heather, moss and lichens. Several small ephemeral streams are activated, on the north side, during p r e c i p i t a t i o n and snow-melt events. The upper portion of the main stream, o r i g i n a t i n g from G a l l i e Pond, becomes inactive during the l a t e r part of the summer, probably caused by high rates of groundwater loss through the lake f l o o r (Gallie, 1983) . The outlet of the lower of the two study basins i s located immediately p r i o r to the confluence with the Ash Lake outlet stream. The flow path of the stream i s mainly through conifer stands with a lush understory of rhododendron and subalpine flowers (species not determined). Groundwater seeps into the stream are v i s i b l e i n a few locations along the flow path. 2.7 PREVIOUS WORK Previous work on the basin includes: sediment y i e l d estimation (Slaymaker, 1977) ; study of surface erosion (Hart, 1978) ; study of s o i l hydrophobicity (Barrett, 1981); study of slope sediment movement (Jones, 1982); analysis of water budget and chemical weathering of Goat Meadows (Gallie, 1983); and lake sediment 19 investigations (Souch, 1984; Owens, 1990). In an adjacent basin research on runoff hydrochemistry has been ca r r i e d out by Zeman and Slaymaker (1975) ; and T e t i (1979) . The above studies i n provide a regional context for th i s study and are discussed i n more d e t a i l where applicable. 20 CHAPTER 3 - FIELD AND LABORATORY METHODS 3.1 STREAM WATER MEASUREMENTS Two 90° sharp crested V-notch weirs were i n s t a l l e d at the outlet of the two basins during the early snowmelt season of 1994. The weirs were b u i l t i n order to obtain a continuous record of hydrological and hydrochemical parameters, which were measured every 10 seconds and stored every 10 minutes i n dataloggers (CR10, Campbell S c i e n t i f i c ) . Ultrasonic Depth Gauges (UDGOl, Campbell S c i e n t i f i c ) were used for continuous stage height ^recordings at the two weirs. The UDGOl's were calibrated by instantaneous discharge measurements at d i f f e r e n t water levels using, the velocity-area method (Goudie, 1990), the time-volume method (Slaymaker, personal communication, 1994) and the 90° V-notch equation (Church and Kellerhals, 1971). A i r temperature (using a 107 Temperature Probe with a 6 Plate Radiation Shield, Campbell S c i e n t i f i c ) was measured immediately adjacent to the UDGOl i n order to c a l i b r a t e i t with a i r density fluctuations. 3.1.1 ELECTRICAL CONDUCTIVITY AND pH E l e c t r i c a l conductivity (EC) using 247 Conductivity Probes (Campbell S c i e n t i f i c ) and pH using SG50CD Sensorex Electrodes with SC32A O p t i c a l l y Isolated RS232 Interface (Campbell S c i e n t i f i c ) , were continuously measured at the outlet of each 21 study b a s i n . EC was cor r e c t e d f o r water temperature (using 107B Temperature Probes, Campbell S c i e n t i f i c ) to 25°C by l a b o r a t o r y c a l i b r a t i o n . The EC-temperature r e l a t i o n s h i p was found to be l i n e a r down to 0.003 mS/cm, wit h an increase of 3.0% per degree C e l s i u s . C a l i b r a t i o n of pH electrodes was c a r r i e d out d a i l y i n the f i e l d u n t i l s t a b l e and there a f t e r checked weekly. 3.1.2 STREAM WATER SAMPLES In order to conduct chemical a n a l y s i s of the stream water at the two s t a t i o n s a t o t a l of 28 depth-integrated hand samples was c o l l e c t e d i n 125 ml acid-washed polyethylene b o t t l e s . Sampling-frequency at the two s i t e s was concentrated around one e a r l y September p r e c i p i t a t i o n event, d a i l y sampling p r i o r to the storm and one sample every two to four hours during the event. The samples were immediately f i l t e r e d a f t e r c o l l e c t i o n using a hand vacuum pump w i t h 0.45 /xm f i l t e r , and stored i n a dark l o c a t i o n c l o s e to 0°C u n t i l a n a l y s i s . The samples were analyzed at the S o i l Science Laboratory of the U n i v e r s i t y of B r i t i s h Columbia f o r major c a t i o n s and s i l i c a using Atomic Absorbtion Spectrophotometry and I n d u c t i v e l y Coupled Plasma Atomic Emission Spectrometry, and f o r major anions using Flow I n j e c t i o n A n a l y s i s . T o t a l Inorganic Carbon (TIC) was analyzed u s i n g a T o t a l Carbon Analyzer at the Department of C i v i l Engineering, U n i v e r s i t y of B r i t i s h Columbia. Throughout t h i s t h e s i s , TIC i s assumed to be present only i n the form of HC03". Charge balance e r r o r f o r the samples was 0.24% wit h a standard d e v i a t i o n of 22 2.84% (see appendix I) . A l l water, sample res u l t s have been converted from concentration into a c t i v i t i e s by using the Debye-Hiickel equation (Drever, 1988) . 35 stream water samples were coll e c t e d for isotopic analysis following roughly the same sampling scheme as those c o l l e c t e d for runoff chemistry (appendix II) . Samples were c o l l e c t e d i n 30 ml polyethylene bottles which were f i l l e d as f u l l as possible and t i g h t l y sealed with parafilm wrap to prevent e q u i l i b r a t i o n with a i r . Samples were analyzed for deuterium and oxygen-18 by Dr. Krouse at Department of Physics and Astronomy, University of Calgary. Isotopic composition of water i s expressed i n per m i l l (&>) deviation from the Standard Mean Ocean Water (SMOW) and i s calculated as: (180(D)) _ (180(D) ) zi8n/n\ (160(H) ) S A M P L E (160(H) ) S M O W SAMPLE- (1*Q{H)) (160(D)) S M 0 W where 1 80 and D are the heavy isotopes oxygen-18 and deuterium, and 1 60 and H are the common isotopes of oxygen and hydrogen. A negative value of §D or 6180 implies that the sample i s depleted of the heavy isotope compared to the SMOW. 23 3.2 PRECIPITATION MEASUREMENTS A 0.1 mm tipping bucket r a i n gauge (TE525M, Campbell S c i e n t i f i c ) was used at the lower station to measure r a i n f a l l i n t e n s i t y . A longitudinal transect of bulk p r e c i p i t a t i o n gauges, mounted 1.5 meters above ground, was established along the stream channel i n order to i d e n t i f y fluctuations and a l t i t u d i n a l differences i n p r e c i p i t a t i o n amounts. The bulk p r e c i p i t a t i o n gauges were emptied following each p r e c i p i t a t i o n event when f i e l d s i t e was occupied, otherwise as soon as possible. The f i v e bulk p r e c i p i t a t i o n gauges were placed at 1530, 1570, 1650, 1740 and 183 0 m.a.s.l. respectively. 3.2.1 PRECIPITATION SAMPLES Pr e c i p i t a t i o n chemistry was sampled i n an acid-washed polyethylene sampler at one s i t e adjacent to the upper station, and i s assumed to represent both wet and dry chemical f a l l o u t (Zeman and Nyborg, 1974). Emptying of the p r e c i p i t a t i o n chemistry sampler was carried out, concurrent with the bulk p r e c i p i t a t i o n gauges.' Storage and chemical analyses of p r e c i p i t a t i o n samples followed' the same procedure as that of stream water samples. The charge balance error was -41.85% with a standard deviation of 10.89% for the four p r e c i p i t a t i o n samples analyzed (appendix I ) . The large charge balance error could be caused by a deficiency of cations i n samples, which presumably results from the d i l u t e p r e c i p i t a t i o n water producing large a n a l y t i c a l errors near the instrumental detection l i m i t . 24 These data are, therefore, used with caution. The EC and pH of the p r e c i p i t a t i o n were measured i n the laboratory using a CDM2e Conductivity meter (Radio Copenhagen) and pHM62 pH meter with glass electrode (Radio Copenhagen),.respectively. Samples for the isotopic composition of ra i n during event #3 were c o l l e c t e d from the bulk p r e c i p i t a t i o n gauges i n order to follow the temporal and a l t i t u d i n a l fluctuations. In t o t a l f i v e p r e c i p i t a t i o n samples were coll e c t e d and analyzed following the procedure of the stream water samples for storage and analysis of i s o t o p i c composition (appendix I I ) . 3.3 MAPPING Maps of the study area were prepared from the following sources: 1) Pemberton topographic map sheet 92 J/7, 1988 edit i o n 2, 1:50000, Department of Energy, Mines and Resources, Canada; 2) Pemberton geology map sheet 92 J/7, 1995 i n press, 1:50000, Geological survey of Canada, compiled by M. Journeay (in press); 3) Black-and-white a e r i a l photographs, taken at 20000 feet, 1990, 30BCB90051, No. 257 and 258; and 4) F i e l d mapping. The topographic maps were used to locate the study area on the 25 B r i t i s h Columbia base map (figure 2.1a) and for generalized contour l i n e s and study basin location i n figure 2.1b. The discrepancy between contour l i n e s from map sheet 92 J/7 and the study basin l i m i t s from f i e l d mapping was not resolved. The loc a t i o n of the contact between Quartz D i o r i t e Complex and Metasediments i n figure 2.1b was obtained from the geology map. A e r i a l photographs and f i e l d • mapping was used for de t a i l e d delineation of the drainage- pattern, vegetation complexes and the study basin boundaries i n figure 2.2a and b. 26 CHAPTER 4 - HYDROLOGY 4.1 DISCHARGE AND ELECTRICAL CONDUCTIVITY Continuous monitoring of discharge and e l e c t r i c a l conductivity (EC) was c a r r i e d out from August 6 to October 8, 1994 (figure 4.1). Extensive snow patches were present i n the study area i n early August, they f i n a l l y disappeared i n the beginning of October. Large diurnal fluctuations i n both discharge and EC were observed throughout August and continued through the remainder of the f i e l d season with smaller and smaller amplitude as the season progressed. During the measurement period f i v e d i s t i n c t p r e c i p i t a t i o n events occurred; August 8-9 (event #1), August 16 (event #2), September 7-9 (event #3), September 10-11 (event #4) and September 30 to October 2 (event #5). These events w i l l be discussed i n d e t a i l i n l a t e r sections with an emphasis on event #3. 4.2 PRECIPITATION There was no detectable systematic a l t i t u d i n a l e f f e c t on p r e c i p i t a t i o n . For the f i v e bulk p r e c i p i t a t i o n gauges located i n a longitudinal transect the four lower gauges show consistent re s u l t s , with less than 5% v a r i a t i o n between s i t e s . The upper most bulk gauge, located on an exposed ridge, has a much di f f e r e n t p r e c i p i t a t i o n pattern. The discrepancy of the upper gauge i s probably caused by an under-catch due to windexposure 27 ^ 20.0 10.0H o.o 0.05 40.0-30.0-1 20.0 10.0H 0.0 Lower Station 9.0 S 7-°: £ 5.0-I 3.0i 1.0-o Aug 10 Aug 20 Septl Sept 10 Sept 20 Oct1 Figure 4.1. Discharge and e l e c t r i c a l conductivity for the entire f i e l d season at the two at the two monitoring stations, and p r e c i p i t a t i o n at the lower station. 28 and i s , therefore, omitted from the r e s u l t s . Good agreement, with less than 8% variation, was found between average c o l l e c t e d bulk p r e c i p i t a t i o n volumes and the ti p p i n g bucket r a i n gauge located at the lower station. The use of the tip p i n g bucket r a i n gauge as a representative p r e c i p i t a t i o n measurement for the entire study basin can, therefore, be j u s t i f i e d . 4.3 RUNOFF RATIO A d i s t i n c t difference i n both discharge and EC between the two measurement s i t e s was observed. Although the upper basin makes up over 75% of the t o t a l study area, the discharge at the lower st a t i o n was approximately. 150% higher than the upper st a t i o n during August and about twice as high during the remaining f i e l d season. The EC was found to be between 3 0% to 60% higher at the lower station compared to the upper one during the early f i e l d season but the difference decreased continuously to about 10% approaching the end of September. The upper st a t i o n also displayed a more random EC signal. Comparison of storm runoff ra t i o s suggests that 13% to 27% of a l l incoming p r e c i p i t a t i o n at the lower station l e f t the lower basin during individual p r e c i p i t a t i o n events, while only 2.8% to 7.7% of p r e c i p i t a t i o n l e f t the upper basin (table 4.1). 29 Table 4.1. Storm runoff r a t i o f o r p r e c i p i t a t i o n events. P r e c i p i t a t i o n Basin Upper Lower Event #1 31.3mm 9 . 5% 5.3% 27 . 0% Event #2 11.0mm 10 .2% 6 .3% 26 . 9% Event #3 2 5.7mm 8 . 5% 5 . 0% 23 . 0% Event #4 10.4mm 4.8% 2 . 8% 13 .4% Event #5 24.3mm 7 . 7% 4 . 0% 23 . 0% There are a number of p o t e n t i a l grounds f o r the i n c o n s i s t e n c y between the two s i t e s . One p o t e n t i a l e x p l a n a t i o n of the discrepancy could be that a large f r a c t i o n of water d r a i n i n g from the upper bas i n does not enter the surface drainage network u n t i l a f t e r the upper measuring s i t e . This would r e s u l t i n a l a r g e r p r o p o r t i o n of groundwater at the lower s t a t i o n which could e x p l a i n the d i f f e r e n c e s i n EC between the s i t e s , as discussed above. This agrees w e l l with the conclusions of G a l l i e (1983) i n the Goat Meadows Basin were he found that a la r g e p r o p o r t i o n of water l e f t the drainage b a s i n through the groundwater system. This process could be enhanced by the h e a v i l y f r a c t u r e d bedrock i n the area, v i s i b l e at exposed outcrops, which could act as e f f i c i e n t h y d r o l o g i c a l conduits i n the subsurface environment. The discrepancy i n discharge between the two s i t e s could a l s o be expla i n e d by measurement i n a c c u r a c i e s . I t i s p o s s i b l e that water d r a i n i n g the upper bas i n bypassed the weir under or on the s i d e of the.V-notch. E r r o r s can a l s o be ass o c i a t e d w i t h c a l i b r a t i o n 30 of the V-notch weirs at each s i t e . Approximate error during peak flow i n discharge measurements at the upper sta t i o n i s 2% (estimated from the difference i n discharge measurements methods, see chapter 3) . The calculated error at the lower s t a t i o n at peak flow i s approximately 20%. The most plausible cause of t h i s large error i s shooting flow through the weir at high water l e v e l s . This would lead to an underestimation of the discharge using the V-notch equation and hence increase the discrepancy between runoff ra t i o s at the two stations even further. It i s further possible that the subsurface divides do not follow t h e i r surface counterparts or that drainage basin areas were not accurately delineated. Errors could also be introduced when mapping the study basins from a e r i a l photographs due to d i s t o r t i o n (Avery and Berlin, 1985), although these maps where checked i n the f i e l d . The stepped topography of the area i s a further source of inaccuracy. 4.4 SUMMARY The continuous record of discharge and EC (depicted i n figure 4.1) demonstrate a large difference between the two monitoring s i t e s . Discharge was found to be between 100% and 150% higher at the lower station although the upper basin makes up over 75% of the t o t a l study area. EC was also much higher at the lower station. The contrast between the two si t e s i s amplified by the 31 runoff r a t i o s f o r the two basins. The lower b a s i n had a runoff r a t i o of 13% to 27% f o r the f i v e monitored storms, whereas only 2.8% to 7.7% of the p r e c i p i t a t i o n could be accounted f o r at the upper b a s i n o u t l e t . The most p l a u s i b l e explanation of the discrepancy between the two basins i s that the upper bas i n i s not h y d r o l o g i c a l l y t i g h t . Water could p o t e n t i a l l y leave the b a s i n through the groundwater system. This process could be enhanced by the h e a v i l y f r a c t u r e d bedrock i n the area a c t i n g as e f f i c i e n t h y d r a u l i c conduits. Re-e n t e r i n g groundwater between the two s t a t i o n s could e x p l a i n the higher EC-signal at the lower monitoring s i t e . 32 CHAPTER 5 - HYDROGRAPH SEPARATION 5.1 INTRODUCTION The storm flow generation at the outlet of each study basin i s evaluated and compared i n thi s chapter. The goal i s to separate the storm runoff into i t s components of storm and pre-storm water. The r e l a t i v e proportion of these contributions during the d i f f e r e n t stages of the storm hydrograph i s useful i n understanding the v a r i a t i o n of stream water chemistry during storm events and between monitoring s i t e s . The question of s p a t i a l and temporal v a r i a b i l i t y of solute composition i n runoff i s further discussed i n chapter 6. The separation of the hydrograph i s pursued for event #3 by using the stable environmental isotopes, oxygen-18 and deuterium, s i l i c a and EC. Except for a few minor snow patches generating a weak diurnal discharge signal, the stream was at baseflow condition p r i o r to the storm which culminated a f t e r four r a i n l e s s days. During the event 22 mm of ra i n f e l l over the basin with a maximum inte n s i t y of 3 mm per hour. The res u l t s using the three methods, isotopes, s i l i c a and EC, are extrapolated to events #1, #2, #4 and #5. Only continuous measurements of EC and discharge are available for these events. The extrapolation i s carried out i n order to examine (1) i f the res u l t s from event #3 are unique or (2) i f the findings are 33 t y p i c a l for other antecedent conditions as well. 5.2. SEPARATION MODELS Tr a d i t i o n a l graphical separation methods of the storm hydrograph by extrapolation of the groundwater recession curve can not explain the dynamic process of hydrological systems, due to the ar b i t r a r y and subjective estimations needed for the use of the method (Hermann and Sti c h l e r , 1980). Growing attention to hydrochemical v a r i a b i l i t y , therefore, led Pinder and Jones (1969) and Hall (1970, 1971) to present a series of simple chemical mixing models. The dynamic mixing model presented by Hal l i s concerned with the relationship between discharge and t o t a l solute load. As the solute concentration varies independently with time from d i f f e r e n t discharge sources the two-component mixing model described by Pinder and Jones (1969) i s used to determine the relationship between tracer concentrations and discharge volumes for two d i f f e r e n t runoff components (equation 2). It can be written as: Qt*Ct = QS*CS + Qp*Cp (2) where Q i s discharge, C i s concentration of applicable tracer and the subscripts t, s and p refer to t o t a l , storm and pre-storm water components respectively. 34 5.3 HYDROGRAPH SEPARATION USING STABLE ISOTOPES The use of s t a b l e n a t u r a l isotopes to separate storm and pre-storm water w i t h the two component mixing model i s p o s s i b l e due to i s o t o p i c f r a c t i o n a t i o n of a i r masses during evaporation and condensation phases (Mazor, 1991). A p r e f e r e n t i a l accumulation of the l i g h t e r isotope i n the l i q u i d phase i s caused by l e s s e f f i c i e n t evaporation and more r a p i d condensation of the heavier i s o t o p e s . The f r a c t i o n a t i o n of isotopes gives r i s e to a l t i t u d i n a l dependence, seasonal f l u c t u a t i o n s and v a r i a t i o n s between i n d i v i d u a l storms (McDonnell et a l . 1990). Hydrograph separation based on s t a b l e isotopes s t a r t e d w i t h s t u d i e s by Dinger et a l . (1970), Martinec (1975) and F r i t z - et a l . (1976) and has been used mainly i n humid temperate regions. Most work employing isotope hydrograph separation has shown a l a r g e pre-storm water component, f r e q u e n t l y g r e a t e r than 70%, during p r e c i p i t a t i o n events (eg. Sklash and Farvolden, 1979a; Hermann and S t i c h l e r , 1980; Bishop, 1990). Both Rhode (1981) and Hooper and Shoemaker (1986) c a l c u l a t e d that a p r e c i s i o n of between ±10% to ±15% can be achieved using n a t u r a l s t a b l e isotopes under favorable c o n d i t i o n s . 5.3.1 RESULTS A s i g n i f i c a n t d i f f e r e n c e between i s o t o p i c composition of the storm and pre-storm component i s necessary f o r the use of 1 80 and D i n hydrograph separation. The weighted mean values of 6 D and 35 6 1 80 f o r p r e c i p i t a t i o n during event #3 was -71.8 w i t h standard d e v i a t i o n of 4.12 §b and -10.6 % with standard d e v i a t i o n of 0.58 lb, r e s p e c t i v e l y (appendix 2) . Average baseflow i s o t o p i c composition at the lower s t a t i o n , estimated from 3 samples taken 101, 74.5 and 2 hours before the outbreak of the r a i n , was -124 %o w i t h standard d e v i a t i o n of 4.4 %o and -17.1 % w i t h standard d e v i a t i o n of 0.17 r e s p e c t i v e l y f o r 6D and 6 1 8 0. For the upper s t a t i o n average baseflow composition of 6D and 6 1 80 was -127 §o w i t h standard d e v i a t i o n of 1.7 tb and -17.1 %b w i t h standard d e v i a t i o n of 0.26 %i> r e s p e c t i v e l y , estimated from 3 samples taken 103.5, 75.5 and 31 hours p r i o r to the s t a r t of the r a i n storm. Figure 5.1 i l l u s t r a t e s the pre-storm water f l u c t u a t i o n s as the discharge increased over 200% at the two s t a t i o n s as estimated w i t h D and 1 8 0 . Appendix I I presents the temporal v a r i a t i o n s i n D and 1 8 0 and the c a l c u l a t e d values f o r the o l d water component i n the storm hydrograph using equation 2. The pre-storm water c o n t r i b u t i o n c a l c u l a t e d using an averaged value of D and 1 8 0 , i s a l s o depicted i n f i g u r e 5.1. Average o l d water c o n t r i b u t i o n s using deuterium and oxygen-18 are between 65% and 89% during peak flow at both s i t e s . 5.3.2 VALIDITY OF METHOD When using n a t u r a l s t a b l e isotopes f o r hydrograph s e p a r a t i o n a number of assumptions or requirements are i m p l i c i t i n the use of equation 2. Assumptions commonly made have been summarized by 36 Upper Station Lower Station 124 • Discharge (l/s) • Deuterium Oxygen-18 Combined Precipitation 248 249 250 251 252 253 Julian day Figure 5.1. Hydrograph separation using natural stable isotopes. 37 Sklash and Farvolden (1979b) as: i) Rain or snowmelt isotopic content can be characterized by a single isotopic value, or v a r i a t i o n i n isotopic content must be documented; i i ) Pre-storm component, groundwater and vadose water, can be characterized by the baseflow with a single isotopic content; i i i ) Isotopic content of p r e c i p i t a t i o n or snowmelt are s i g n i f i c a n t l y d i f f e r e n t from pre-storm values; and iv) Contribution of stored surface water to the stream i s i n s i g n i f i c a n t . The v a l i d i t y of the isotope hydrograph separation assumptions has been e x p l i c i t l y questioned by Kennedy et a l . (1986). Their c r i t i c i s m i s based on one exceptionally large storm over the Mattole River basin of northwestern C a l i f o r n i a , where both oxygen-18 and deuterium data suggested that the pre-storm contribution to the storm hydrograph by far exceeded the storage capacity of the watershed. In t h e i r discussion of assumption ( i ) , Kennedy et a l . (1986) suggest that the average iso t o p i c composition of the r a i n does not necessarily correspond to that of the average surface runoff water. Light to moderate-i n t e n s i t y r a i n may i n f i l t r a t e completely whereas heavy r a i n with a d i f f e r e n t isotopic composition may run off, at least p a r t l y , on the surface. The hydrophobicity of the s o i l i n the f i e l d area 38 described by Barrett (1981) and Barrett and Slaymaker (1989) probably prevents the potential problem of r a i n water p a r t i t i o n i n g due to di f f e r e n t p r e c i p i t a t i o n i n t e n s i t i e s . A l l ra i n water f a l l i n g on vegetated areas i n the basin w i l l t r a v e l as overland flow u n t i l i t can enter the subsurface environment through the macropore system. The r e l a t i v e l y constant p r e c i p i t a t i o n i n t e n s i t y of event #3 further reduces the p r o b a b i l i t y of p a r t i t i o n i n g of surface and subsurface runoff (figure 5-. 1) . The v a l i d i t y of assumption ( i i ) , that the isotopic content of the baseflow r e f l e c t s stored water i n the s o i l and groundwater reservoirs, can also be debated. DeWalle et a l . (1988) found a s i g n i f i c a n t difference i n isotopic content between groundwater and vadose water i n a small Appalachian forested catchment. Instead of a general c r i t i q u e of the method, they further subdivided the stormflow, using a three-component mixing model, into groundwater, s o i l water and direc t channel p r e c i p i t a t i o n . Although the study by DeWalle et a l . (1988) does not e x p l i c i t l y refute the two-component model, t h e i r findings raise questions about possible erroneous pre-storm component calculations when using a two component mixing model. No attempt was made to use the three component mixing model i n thi s study. It does not seem l i k e l y that a large f r a c t i o n of water w i l l be contributed from the vadose zone i n the study area as most of the s o i l horizon i s believed to be bypassed due to i t s compact and hydrophobic 39 nature. It i s possible,, however, that there could be a change i n p a r t i t i o n i n g between deep and more shallow groundwater components with d i f f e r e n t isotopic composition, during the hydrologic event. The l a s t assumption, that the isotopic composition of surface storage could be affected by evaporation, may be a source of error i n the storm hydrograph separation c a l c u l a t i o n s . The surface storage i n the small ponds i n the basins are considered n e g l i g i b l e due to the small storage capacity, but a few small snow patches contributed an unknown volume of water during the event. It i s , however, not l i k e l y that the melt water contribution p r i o r to the event was s i g n i f i c a n t l y d i f f e r e n t from that during the r a i n storm and was, therefore, accounted for i n the sampling scheme of the baseflow isotopic composition. A further problem with the isotopic separation method i s that the r a t i o between the heavy and the normal isotopes i s not p e r f e c t l y conservative. It i s possible that the oxygen r a t i o can change as a result of both isotopic f r a c t i o n a t i o n and molecular exchange (Bishop, 1990) . Molecular exchange occurs as a consequence of atom substitution between water and other oxygen-r i c h molecules i n the subsurface environment. According to Bishop (1990), Rhode (1987) calculated that the e f f e c t of molecular substitution i s neg l i g i b l e during r a i n f a l l events, but can possibly be s i g n i f i c a n t during spring-melt runoff. . 40 Isotopic f r a c t i o n a t i o n results from d i f f e r e n t i a l evaporation of i s o t o p i c a l l y l i g h t e r molecules, thus leading to an enrichment of the remaining water with heavy isotopes and, therefore, to an overestimate of the pre-storm component i n runoff. The isotope r a t i o s of deuterium and oxygen-18 of the c o l l e c t e d isotope samples f a l l close to the meteoric water l i n e for the northern hemisphere (Dansgaard, 1964), see figure 5.2. This supports the assumption that the isotopic composition has not been changed due to secondary processes, such, - as evaporation p r i o r to i n f i l t r a t i o n or of water stored i n aquifer, or molecular exchange between water and bypassed s o i l and rock material. 5.4 HYDROGRAPH SEPARATION USING SILICA The use of s p e c i f i c ion concentrations i n order to i d e n t i f y d i f f e r e n t water sources contributing to the runoff hydrograph has been successful i n many cases. Depending on bedrock geochemistry, s o i l c h a r a c t e r i s t i c s and p r e c i p i t a t i o n chemistry, d i f f e r e n t chemical species can be u t i l i z e d . One of the most commonly used ions for hydrograph separation i s s i l i c a (ie. Maule and Stein, 1990). Kennedy (1971) showed that p r e c i p i t a t i o n , which has a s i l i c a content close to zero, or at least below the a n a l y t i c a l detection l i m i t , w i l l reach equilibrium concentrations with regards to s i l i c a within a few minutes to hours of contact time 41 -70--80--90-E _g o +-< D CD Q -100--110 -120--130 M e t e o r i c I s o t o p e L i n e Lower Station • • Upper Station + Precipitation Meteoric Line i i i i 1 1 1 18 -17 -16 -15 -14 -13 -12 -11 -10 Oxygen-18 Figure 5.2. Meteoric isotope l i n e for northern hemisphere. 42 with the mineral matrix. Kennedy concluded that because i t s rapid e q u i l i b r a t i o n , s i l i c a could p o t e n t i a l l y be used as a hydrological tracer. Zeman and Slaymaker (1975) confirmed Kennedy's conclusions, but i t was not u n t i l the mid 1980's that s i l i c a was tested against natural stable isotopes (Hooper and Shoemaker, 1986) . 5.4.1 RESULTS Implicit i n Kennedy's (1971) findings, i s that the use of s i l i c a i s based on the assumptions that the storm water s i l i c a concentration i s equal to zero and the pre-storm concentration i s equal to that of baseflow. The s i l i c a concentration i n p r e c i p i t a t i o n was found to be below the detection l i m i t (<3.0*10~ 6 M) for the four r a i n samples collected. The average baseflow concentration of s i l i c a at the upper station was 1.09*10-4 M sd 3.60*10"6 M, for three samples taken 127.5, 75.5 and 31 hours before the r a i n f a l l started. The average s i l i c a concentration of baseflow for the lower station was 1.05*10~4 M sd 5.77*10"7 M estimated from three samples collected 73.5, 29, and 2 hours p r i o r to the onset of rain storm (figure 5.3). At the upper basin outlet the s i l i c a tracer indicated a 50% to 68% pre-storm water contribution (figure 5.3) at peak flow. The pre-storm contribution calculated using s i l i c a as a tracer shows an approximately 20% lower value than when using isotopes for the same s i t e . At the lower station the pre-storm 43 Upper Station Lower Station 124 • Discharge (l/s) EC • Silica Isotopes 248 249 250 Precipitation 251 252 Julian day 1 t l l 1 1 ~ 253 Figure 5.3. Hydrograph separation using e l e c t r i c a l conductivity, s i l i c a and stable isotopes. 44 contribution at peak flow i s nearly consistent with the res u l t using oxygen-18 and deuterium, namely 67% to 89% pre-storm water. 5.4.2 VALIDITY OF METHOD In studies comparing chemical and isotopic tracers both Hooper and Shoemaker (1986) and Wels at a l . (1991) achieved a consistent higher pre-storm component with s i l i c a than with oxygen-18 and deuterium. Neither set of researchers suspected an overstatement of the pre-storm water with the s i l i c a tracer, rather they assumed an underestimate using isotopes. Wels and his companions j u s t i f y t h e i r discrepancy as a r e s u l t of incomplete mixing i n the soil/groundwater reservoir, whereas Hooper and Shoemaker found no physical explanation. The rapid e q u i l i b r a t i o n of water can p o t e n t i a l l y lead to an increased dissolved s i l i c a load af t e r a b r i e f contact with mineral and organic material. An overstatement of the pre-storm component could, therefore, result from p r e c i p i t a t i o n water entering the stream v i a overland flow. Another problem with using s i l i c a as a hydrological tracer may be found i n b i o l o g i c a l l y productive water due to dissolved s i l i c a uptake by diatoms (Hooper and Shoemaker, 1986), which would lead to an underestimate of the pre-storm component. This i s not l i k e l y to be a problem i n the study basin under consideration due to the d i l u t e character and low b i o l o g i c a l productivity of the 45 alpine/sub-alpine stream water i n the study area. Underestimates of the pre-storm component at the study s i t e s could, however, arise from f a i l u r e of the pre-storm water to reach near equilibrium or steady state a c t i v i t y with regard to s i l i c a p r i o r to the hydrological event. Even though Kennedy (1971) proposed very rapid e q u i l i b r a t i o n reactions, t h i s could be a pote n t i a l problem i n • coarse material such as the talus slope, on the north side of the study basin, where the mineral surface area i s comparably small. This could explain the discrepancy between the study s i t e s , with an underestimate of the upper station flowing along the. bottom of the south-facing talus slope concurrent with an agreement between s i l i c a and isotope separation for the lower stream which flows mainly through vegetated areas. 5.5 HYDROGRAPH SEPARATION USING ELECTRICAL CONDUCTIVITY Pinder and Jones (1969) and Nakamura (1971) were among the f i r s t to involve chemical tracers i n the analysis of hydrographs. In t h e i r work they used EC as an indicator of r e l a t i v e amount of storm and pre-storm water. The theory behind t h i s hydrograph separation method i s that the concentration of solutes i n d i r e c t channel p r e c i p i t a t i o n and surface runoff i s very low i n comparison to the subsurface component. Due to the difference i n concentration between storm and pre-storm water, the two-component mixing model can be applied (equation 2). 46 5.5.1 RESULTS The e l e c t r i c a l conductivity of the ra i n water was 6.15 /zS/cm with a standard deviation of 1.57 zzS/cm estimated from four r a i n water samples taken during the duration of the f i e l d season. The EC of the baseflow for the upper station immediately p r i o r to the onset of the storm was 21.1 zzS/cm. The average baseflow EC for the four days p r i o r to the ra i n was 28.45 /zS/cm with a standard deviation of 4.3 6 /zS/cm. The lower reading for EC was chosen as a representative value for baseflow, at the upper station, due to the better f i t to the pre-storm estimates achieved using the more conservative tracers of s p e c i f i c s i l i c a concentration and the natural isotopes (figure 5.3). The calculated pre-storm component using EC demonstrates a very random contribution and does not correspond well with the resu l t s achieved using isotopes and s i l i c a as hydrograph separation tracers. At the lower station the average EC for the four days preceding event #3 was 39.00 /zS/cm with a standard deviation of 1.39 /zS/cm which was taken as a representative pre-storm value. This i s close to the EC value 39.39 /zS/cm immediately p r i o r to the storm. The hydrograph separation at the lower station followed the general pre-storm contribution trend calculated with stable isotopes and s i l i c a concentration, but demonstrated a 10% to 20% lower pre-storm contribution (figure 5.3 see also appendix IV). 47 5.5.2 VALIDITY OF METHOD As with the other hydrological tracers discussed above, Pinder and Jones (1969) and Nakamura (1971) concluded from t h e i r studies that d i l u t i o n smaller than expected during storm peak flow r e s u l t s from a large pre-storm contribution. Similar r e s u l t s , but with d i f f e r e n t conclusions, were presented by Pilgrim et a l . (1979) . They suggested that the constant high conductivity was a consequence, due not only to increased groundwater discharge, but also to a substantial dissolved load obtained by the storm component during i t s b r i e f contact with the s o i l surface. This could be a problem i n the study area since much of the storm water i s believed to move, at least p a r t l y , as overland flow (Barrett, 1981). A flushing e f f e c t caused by the overland flow during i n i t i a t i o n of the p r e c i p i t a t i o n event could conceivably explain why the correspondence between EC and the other tracers used i n t h i s study i s better at the'onset of the storm than at peak flow. The use of EC i s further limited as variations i n s p e c i f i c ion concentration may change i n d i v i d u a l l y throughout d i f f e r e n t stages of the storm (De Boer and Campbell, 1990) . An additional complication i s caused by the fact that EC i s a measure of the t o t a l charge strength of water and not of the t o t a l a c t i v i t y . A monovalent species w i l l , . therefore, contribute only half that of an equivalent concentration of a divalent species to the EC-si g n a l . Problems a r i s i n g from d i f f e r e n t i a l changes i n in d i v i d u a l 48 ion concentrations were, however, overcome i n t h i s study by analyzing a l l major ions at di f f e r e n t stages of event #3 (see appendix I ) . Due to the ki n e t i c s of rock dissolution, EC is- not l i k e l y to reach near equilibrium or steady state a c t i v i t i e s f or a l l the d i f f e r e n t ions i n the macropores and i n the coarse talus material, which characterizes much of the drainage basin, during the r e l a t i v e l y short residence time of water i n the subsurface environment. This p o t e n t i a l l y explains the discrepancy between the calculated pre-storm contribution compared to the other tracers discussed i n th i s paper. The advantage of EC, compared to other tracers used i n t h i s study, i s that i t can be measured continuously. By c a l i b r a t i n g EC against more conservative tracers i t can be u t i l i z e d for hydrograph separation when hand or automatic sampling i s not possible (Sklash and Farvolden, 1979a; De Boer and Campbell, 1990). The next section w i l l discuss the r e l i a b i l i t y of using EC for hydrograph separation at the two study s i t e s and i f i t i s possible to extrapolate the results from event #3 to other p r e c i p i t a t i o n events. 5.6 EXTRAPOLATION OF HYDROGRAPH SEPARATION In order to determine whether the large pre-storm water contribution during event #3 was a unique occurrence or whether 49 the same contribution could be expected from a range of antecedent conditions the p o s s i b i l i t y of extrapolating the tracer data was tested for storms when only EC and discharge was monitored. Because of the non-uniformity of the data and the r e l a t i v e l y small sample size, the Friedman analysis of variance ranking was used to examine i f there were any systematic vari a t i o n s between using EC and s i l i c a / s t a b l e isotopes as hydrological tracers (table 5.1). It i s apparent from table 5.1 that EC can not be used as an a l t e r n a t i v e tracer for stable isotopes and s i l i c a i n hydrograph separation for the upper basin. At the lower basin, however, the Table 5.1. Comparison between hydrological tracers using Friedman analysis of variance. e l e c t r i c a l conductivity Significance at the 95% l e v e l UPPER STATION s i l i c a 0 . 89* NO isotopes 0 . 76* NO LOWER STATION s i l i c a 0.94* YES isotopes 0 . 94* YES * Kendall Coefficient of Concordance sig n i f i c a n c e at 95% l e v e l between s i l i c a / s t a b l e isotopes and EC enables the use of EC as a tracer i n hydrograph separation at t h i s s i t e (figure 5V4a and b) . Due to the e q u i l i b r a t i o n 50 constraints of EC discussed above and the fact that EC showed 10% to 20% lower pre-storm contribution for event #3, we can assume that EC gives a conservative measure of the pre-storm contribution during peak flow. It i s , however, possible that flushing of r e a d i l y soluble material at the soil/vegetation surface during overland flow (as discussed above) could lead to a somewhat overestimated pre-storm water contribution at the commencement of the storm event.. By using EC as a hydrological tracer for the four remaining hydrological events monitored i t suggested that the large pre-storm component found at event #3 i s t y p i c a l (figure 5.4a and b) . The hydrograph separation covers a range of p r e c i p i t a t i o n events from early August with baseflow close to 20 1/s to end of September with base flow less than 2 1/s. A l l events depict a large pre-storm component (above 50% and up to 80%), e s p e c i a l l y notable at the onset of peak flow. The increased storm water component i n the l a t e r part of the peak flow could r e s u l t from depletion of hydrological storage i n the basin. 5.7 SUMMARY The old water contribution during event #3 using the stable environmental isotopes, oxygen-18 and deuterium, s i l i c a and EC was 56% to 86% during peak flow at the lower station. At the 51 228 Julian Day Q Precip Old water (EC) Figure 5.4a. Hydrograph separation of event #1 and #2 at the lower monitoring station using e l e c t r i c a l conductivity. 52 -6 254 255 Julian Day » . . . . ! . i 1 : E o 275 Julian Day P~"' 1 P r e c " P • Old Water (EC) Figure 5.4b. Hydrograph separation of event #4 and #5 at the lower monitoring station using e l e c t r i c a l conductivity. 53 upper sta t i o n the old water contribution was 50% to 87% at peak flow using isotopes and s i l i c a and down to 24% for EC for the same event. When comparing the four tracers used i n the hydrograph separation at the study s i t e , two features are immediately apparent. F i r s t , the predictions of pre-storm contribution by d i f f e r e n t tracers agree well at the lower s i t e but disagree at the upper basin. Secondly, pre-storm water contribution predicted by isotope calculations i s consistent for both s i t e s . It i s apparent from the discordant pre-storm water contribution r e s u l t s between isotopic and chemical tracers at the upper stat i o n that the water i n the subsurface environment does not reach equilibrium or steady state a c t i v i t i e s with surrounding mineral phases. There are two possible physical explanations of t h i s phenomenon: 1) Pre-storm water residence time i s too short; or 2) Pre-storm water reservoirs consist of very coarse material with a r e l a t i v e l y small surface area. As was noted i n the introduction, residence time of water i n hydrological reservoirs i s often short i n mountainous environments, due to steep slopes, shallow and compacted s o i l s and coarse material. This i s further enhanced i n the upper basin 54 where the main stream flows primarily on the boundary between hydrophobic s o i l s and a coarse talus slope. The lower basin stream on the other hand flows through primarily vegetated areas with more permeable s o i l s . The differences i n the near stream zone between the basins could explain the discrepancy between re s u l t s using chemical tracers at the two s i t e s . The re s u l t s using the three methods, isotopes, s i l i c a and EC, were further extrapolated for the r a i n storms when only EC was monitored. It was found that EC was a useful alternative tracer at the lower station but could not be used at the upper one. The extrapolation showed that a large pre-storm component could be expected for other antecedent conditions than those of event #3. 55 CHAPTER 6 - CHEMICAL CHARACTERISTICS 6.1 INTRODUCTION The purpose of t h i s chapter i s to investigate the temporal and s p a t i a l v a r i a b i l i t y of the stream water chemistry at the two study basins. The chemical c h a r a c t e r i s t i c s of the stream water w i l l be analyzed using three d i f f e r e n t approaches; mass balance, s t a t i s t i c a l and thermodynamic. The mass balance approach i s used to correlate stoichiometry of the bedrock mineralogy to dissolved constituents i n the stream water. Following, the approach of Garrels and Mackenzie (1967), mass balance calculations are here used to interpret r e l a t i v e solute contributions from d i f f e r e n t mineral sources. Linear c o r r e l a t i o n i s used to investigate the s t a t i s t i c a l association between discharge and individual chemical species. S t a t i s t i c a l relationships between natural waters and environmental parameters are useful tools when i d e n t i f y i n g b i o l o g i c a l , chemical and hydrological processes within drainage basins (e.g. Eriksson, 1985), but do not es t a b l i s h any cause-and-effect correlations. F i n a l l y , a thermodynamic technique i s used to evaluate the extent to which stream water could be represented as an equilibrium system and changes over the course of the storm. An attempt i s also made to fin d a the o r e t i c a l hydrochemical 56 evolution path of the stream water chemistry and secondary mineral formation. 6.2 MASS-BALANCE APPROACH Mass balance calculations can be applied to hydrochemical data i n order to interpret the r e l a t i v e stoichiometry of rock material encountered. In general terms the stream water chemistry can be characterized by the simple mass balance equation; Material i n solution - Atmospheric input = Rock material - So l i d residue + cation exchange + biomass Garrels and Mackenzie (1967) were among the f i r s t to test the mass-balance technique on the hydrochemistry of natural waters i n order to interpret the o r i g i n of the chemical composition. The approach has since been used i n several studies for inte r p r e t i n g both chemical weathering mechanisms and rates of mineral weathering (eg. Andersson-Calles and Eriksson, 1979; Velbel, 1986 and Mast et a l . 1990). A mass-balance c a l c u l a t i o n can be made to f i n d the o r i g i n of the t o t a l a c t i v i t i e s along a reaction path i f the water composition of the i n i t i a l (ie. precipitation) and f i n a l (ie. baseflow) hydrochemical composition are monitored together with a defined set of geochemical reactants and products. In order for t h i s to 57 work s a t i s f a c t o r i l y i t i s necessary to consider only a few id e a l i z e d minerals representing a known range of mineral stoichiometry i n the basin (Plummer and Back, 1980) . In addition to the problem of mineral stoichiometry the ki n e t i c s of the system must be evaluated including very reactive minerals i n small quantities and excluding inert minerals. Knowing that the majority of the study area i s underlain by quartz d i o r i t e (Gallie, 1983 and Journeay, i n press) a s i m p l i f i e d geological bedrock composition can be assumed (table 6.1). Table 6.1. Assumed major minerals contributing to hydro-chemistry . Minerals Stoichiometry Solutes Hornblende Ca 2Na 2Mg 2Al 2Si 60 2 2 (OH)2 Ca 2 +, Na+, Mg2+ K-Feldspar KAlSi 30 8 K+ Anorthite CaAlSi 20 8 Ca 2 + A l b i t NaAlSi 30 8 Na+ Quartz Si0 2 Inert Pyrite FeS04 so42-6.2.1 RESULTS Three important assumption were made applying the mass balance approach i n t h i s study. F i r s t , the secondary mineral formation was proposed to be ka o l i n i t e (Al 2Si 20 5 (OH) 4) . The assumption that k a o l i n i t e was the major secondary product i s consistent with the pred i c t i o n based on thermodynamic s t a b i l i t y (figure 6.1). Second, release from cation exchange reactions i n s o i l s i s assumed small compared to the net cation flux i n the study area. 58 The t h i r d assumption i s that biomass represents steady state elemental cycling. The l a s t two assumptions are further discussed i n section 6.3 where I w i l l argue that although cation exchange reactions i n soils, and biomass cycli n g can not be e n t i r e l y disregarded their' contribution during the monitored storm event i s i n s i g n i f i c a n t . Back-reacting the s o l i d residue with.the hydrochemistry enables the r e l a t i v e contribution of individual minerals to be calculated (table 6.2) . F i r s t , p r e c i p i t a t i o n chemistry was subtracted from the stream water chemistry. Second, a l l Mg was back-reacted with k a o l i n i t e and other species necessary to balance the reaction i n order to produce hornblende. Third, remaining K, Na and Ca was back-reacted with k a o l i n i t e to make K-feldspar, a l b i t e and anorthite respectively. F i n a l l y , sulphate was used to produce p y r i t e . Table 6.2. Mass-balance reactions. Kaolinite + 5Mg2+ + 2Ca 2 + + 2Na+ + 16HC03~ + 4H 4Si0 4 = . Hornblende + 16C02 + 17H20 Kaoli n i t e + 2K+ + 2HC03" + 4H 4Si0 4 = 2K-f eldspar+2C0 2 + llH 20 Kaolinite + Ca 2 + + 2HC03' = Anorthite + 2C02 + 3H20 Kaolinite+ 2Na+ + 2HC03' + 4H 4Si0 4 ' =2Albite+ 2C02 + 11H20 Fe 2 + + S042' = Pyrite It was found from the mass-balance calculations that close to 50% of stream flow hydrochemical load i n the study area originated from weathering of anorthite (table 6.3). The high 59 anorthite contribution of solutes i s much higher than the proportion of anorthite found i n the study s i t e bedrock, which was less then 10% (Gallie, 1983). It does, however, agree well with other hydrochemistry studies i n both lowland areas (Clayton, 1988) and i n mountain environments (Williams et a l . 1993 and Brown personal communication, 1995) . Clayton (1988) suggests that such discrepancy could be a re s u l t of incongruent release of cations from anorthite, which may r e s u l t from heterogeneities within minerals. Preferential release of cations from the s o l i d phase could also be a result of disproportionate d i s s o l u t i o n from exchange reactions with hydrogen ions i n solution (Chou and Wollast, 1985). Chou and Wollast observed i n laboratory studies that nonstoichiometric d i s s o l u t i o n was an i n i t i a l transient state l a s t i n g of the order of minutes to days before a steady state, stoichiometric dissolution, took over. The process described by Chou and Wollast (1985) could, therefore, be responsible for the large Ca a c t i v i t i e s present i n the study area where the water residence time i s low and physical weathering i s a c t i v e l y producing fresh new mineral surface areas. Although c a l c i t e often i s not observed i n geochemical analysis i t . .is possible that very small amounts (much less than 1%) could be the main o r i g i n of large Ca a c t i v i t i e s (Mast et a l . 1990). They further suggest that eolian dust of calcium carbonate could be another plausible source of dissolved calcium i n surface waters. Small amounts of pyrite are ubiquitous i n the basin, and hence 60 the probable source of the large sulphate a c t i v i t i e s i n the runoff. Oxidation of pyrite generates hydrogen ions, which p o t e n t i a l l y provides the driv i n g force for chemical weathering i n the study area. The small standard deviation through-out event #3 (table 6.3, see also appendix V) demonstrates that there i s l i t t l e temporal v a r i a t i o n i n minerals contributing solutes Table 6.3. Relative contribution of minerals to hydro-chemistry . Mineral Upper basin Standard deviation Lower basin Standard deviation Anorthite 47% 1.3% 47% 1. 0% A l b i t e 14% 1. 0% 13% 0 .3% K-feldspar 5% 0 .2% 5% 0 . 2% Hornblende 10% 0.3% 10% 0 .3% Pyrite 24% 1. 2% 25% 0 . 9% Error % H4Si04 17% 6.2% 13% 5 .2% HC03" -36% 7 .4% -50% 5 .4% HC03" 1 1 -30% 7 . 6% -45% 5 . 5% H C O 3 " 1 1 1 22% 6 . 0% 16% 5 .4% * Quantification of errors i s made by comparing s i l i c a and bicarbonate residual a c t i v i t i e s with those of the hydrochemistry. Bicarbonate i s needed for charge balance mass-balance equations, however, charge balance can also be j u s t i f i e d by buffering hydrogen ions contributed from 1 1 rain, and 1 1 1 oxidation of py r i t e . (sample B l l has been omitted from c a l c u l a t i o n as i t was assumed an o u t l i e r ) . Although there i s a s i g n i f i c a n t d i l u t i o n e f f e c t 61 during the event the mass-balance approach suggests that the r e l a t i v e proportion of contributing minerals i s constant throughout the storm. There i s , further, an i n s i g n i f i c a n t difference between the upper and lower station i n minerals responsible for the hydrochemical c h a r a c t e r i s t i c s of the runoff. 6.2.2 VALIDITY OF APPROACH The mass-balance approach assumes that observed pre-storm water composition i s due to weathering of primary minerals and production of a secondary phase. This implies that solute contribution from s o i l s and biota i s i n s i g n i f i c a n t , which can only be considered correct i f the s o i l column i s bypassed and vegetation experiences steady state conditions. This w i l l be discussed further i n the next section. The q u a n t i f i c a t i o n of errors i n table 6.3, suggests that the calculations predict a residue of both s i l i c a and hydrogen ions. The underestimation of s i l i c a i n the mass-balance for the upper and lower basin of 17% and 13% respectively, could be a r e s u l t of k i n e t i c b a r r i e r s forming s i l i c a depleted phases such as gibbsite (A1(0H)3) instead of always producing k a o l i n i t e as a secondary mineral. This could further explain the difference between the two s i t e s , where the upper basin depicts a larger s i l i c a residue but also experiences more d i l u t e water. The underestimation i n the charge balance a f t e r bicarbonate, hydrogen ions from r a i n and from oxidation of p y r i t e have been 62 accounted for i s not well understood. The significance of the assumed- mass-transfer reactions i s reduced by the fact that other minerals, or the same minerals with s l i g h t l y d i f f e r e n t stoichiometry, may be involved i n weathering. This problem i s enhanced at the study s i t e due to the geological complexity of the basin. Although metasediments compose only a small percentage of the north-facing slope, much mixing of t h i s rock type has p o t e n t i a l l y occurred i n the talus. The primary mineralogical difference between the two main rock types i s the large proportion of a c t i n o l i t e and c h l o r i t e i n the metasediments (Gallie, 1983). A c t i n o l i t e i s stoichiometrical.ly close to hornblende, but does not contain Na, c h l o r i t e i s a pote n t i a l source for Mg. A further problem i s that the mass-balance calculations above i n f e r a closed system with respect to carbon dioxide. This can be an erroneous assumption i n the study area, e s p e c i a l l y i n the coarse talus material where much a i r can interact with water i n the subsurface environment. An open system, however, would increase the production of hydrogen ions i n the runoff and thus increase the charge balance error. 6.3 STATISTICAL APPROACH The s t a t i s t i c a l relationship between solute a c t i v i t y and stream discharge i s useful when id e n t i f y i n g b i o l o g i c a l , chemical and 63 hydrological processes within drainage basins. In a lowland study i n central Sweden, Grip (1982) found interdependence between flow rate and d i f f e r e n t chemical elements. His s t a t i s t i c a l analysis showed positive c o r r e l a t i o n between the concentration of weathering products and low discharge during base flow, and between high discharge during storm flow and the concentration of b i o l o g i c a l l y ' e s s e n t i a l species. Similar findings to those of Grip (1982) have been observed i n mountain environments by Zeman and.Slaymaker (1975); M i l l e r and Drever (1977a); Stednick (1987) and Diez et a l . (1991). They generally found that the sources of d i f f e r e n t elements and t h e i r concentrations responded d i f f e r e n t l y to changes i n flow. With increasing streamflow those elements of l i t h i c o r i g i n , such as sodium, magnesium, and s i l i c a decrease i n concentration. Species associated with organic materials increased i n concentration with raised discharge, while species with several sources, such as potassium and calcium, changed according to the main source p r e v a i l i n g under each runoff condition. 6.3.1 RESULTS Linear c o r r e l a t i o n between solute a c t i v i t i e s for i n d i v i d u a l chemical species and discharge were calculated to investigate the existence of s i g n i f i c a n t relationships between the discharge and the chemical parameters i n the study area. The r e s u l t s from the c o r r e l a t i o n analysis are shown i n table 6.4. In general a l l 64 constituents except hydrogen ions, exhibit a s i g n i f i c a n t flow d i l u t i o n relationship. The posit i v e c o r r e l a t i o n between hydrogen ions and discharge i s probably caused by di r e c t channel p r e c i p i t a t i o n and overland flow introducing acid r a i n water into the stream, hence lowering pH of the stream water during the storm event. Prior to the onset of the p r e c i p i t a t i o n event stream pH was between 7.3 and 7.6. The introduction of acid r a i n water (pH=5.04) lowered the pH of the stream water to a lowest point of 6.96. Table 6.4. Correlation between discharge and in d i v i d u a l solutes. Species Upper basin Significance at 95% l e v e l Lower basin Significance at 95% l e v e l K+ -0 . 63 YES -0.57 YES Na+ -0 . 44 NO -0.81 YES Ca 2 + -0 . 76 YES -0.79 YES Mg2+ -0 . 77 YES -0.81 YES H 4Si0 4 -0 . 84 YES -0 . 83 YES S042" -0 . 77 YES -0 . 82 YES HC03- -0 . 67 YES -0 . 72 YES H+ +0.67 . YES • +0.78 YES EC -0 . 74 YES -0 . 74 YES At the upper station, the Na a c t i v i t y i s behaving somewhat d i f f e r e n t l y from other measured major ions. The lower d i l u t i o n of Na may be caused- by incongruent weathering of the glass f r a c t i o n of volcanic ash, which i s well d i s t r i b u t e d i n Goat Meadows s o i l s (Gallie, 1983) . This could suggest that the water 65 flow path i n the upper basin does not e n t i r e l y by pass the s o i l column. G a l l i e (1983) suggests that water i n the Goat Meadows Basin p a r t l y flows through saturated fingers, which may develop due to s p a t i a l v a r i a b i l i t y i n surface water-repellency or dynamic i n s t a b i l i t y caused by hydraulic conductivity differences. At the lower station K experiences somewhat less d i l u t i o n during high flow than do other major ions. This could p o t e n t i a l l y be an ef f e c t of leaching of organic material during overland flow. The lower d i l u t i o n of Na at the upper and K at the lower basin suggests that sources other then bedrock are l i k e l y contributing c e r t a i n solutes to the streams i n the study area. The ef f e c t of Na and K are, however, not s t a t i s t i c a l l y s i g n i f i c a n t and should, therefore, be interpreted with caution. 6.4 THERMODYNAMIC APPROACH Thermodynamics of chemical weathering reactions are used here to examine the extent to which sampled stream water data i s i n equilibrium with the minerals present i n the study area. The approach of graphical representation using chemical thermodynamics i n order to i d e n t i f y the s t a b i l i t y r e l a t i o n s h i p between solutes and minerals i n natural waters has been used frequently i n the l i t e r a t u r e (eg. M i l l e r and Drever, 1977b, Williams et a l . 1993). 66 Recently the interpretation of more complex chemical processes i n aqueous systems has been carried out using computer modelling programs, which allow the user to simulate various processes occurring between waters and minerals. Examples of such programs are GEOL PATH (Brown and Perkins, 1978), SOLGASWATER (Eriksson, 1979) and SOLMINEQ. 8 8 (Perkins, 1988) but more than 50 other programs are available that calculate chemical equilibrium i n natural waters (Nordstrom and B a l l , 1984). An attempt w i l l be made, here to f i n d a theoretical hydrochemical evolution path of the stream water chemistry and secondary mineral formation using the program GEOL PATH. 6.4.1 RESULTS Mineral s t a b i l i t y diagrams (figure 6.1) based on thermodynamic relationships from, Brown and Perkins (1978), show that stream waters for event #3 plot i n the k a o l i n i t e s t a b i l i t y f i e l d . S t a b i l i t y diagrams are plotted assuming Al i s inert and that water temperature i s 25° C. K/H-H4Si04 and Na/H-H4Si04 s t a b i l i t y diagrams show sim i l a r results to the Ca/H2-H4Si04 diagram depicted i n figure 6.1. The f i e l d data plotted i n the s t a b i l i t y diagram depict an elongated pattern for the two stations. The plotted samples to the right are from base flow whereas those to the l e f t are from peak discharge. 67 6.4.2 MODEL CALCULATIONS The t h e o r e t i c a l hydrochemical evolution pathway depicted i n figure 6.1 i s estimated using the reaction-path program, GEOL PATH (Brown and Perkins, 1978). GEOL PATH i s a modification of the pioneering program, PATHI (Helgeson et a l , 1970) . The program calculates the d i s t r i b u t i o n of species i n an aqueous solution, assuming that chemical equilibrium i s maintained between the solution and secondary minerals. The program further uses i r r e v e r s i b l e mass transfer between solution and reactant minerals not i n equilibrium to calculate the evolution pathway of a set of i n i t i a l constraints. A number of assumptions were made regarding i n i t i a l constraints i n the model calculations. F i r s t , major ions i n the i n i t i a l s o lution are considered equal to the p r e c i p i t a t i o n chemistry i n the study area. For solutes below the detection l i m i t , an a c t i v i t y of 50% of the l i m i t was chosen. Second, pH of the i n i t i a l solution was calculated by adding hydrogen ions from i) ra i n water, and i i ) oxidation of pyrite (derived from mass balance c a l c u l a t i o n s ) . Third, i n i t i a l reactants are set to the r a t i o of minerals contributing solutes to runoff as.calculated by the mass balance approach (except pyrite which has already been accounted f o r ) . 68 22-18-16-14-< + X C O + 12-CM crj O cd o) 1 0 " o 4H Gibbsite S t a b i l i t y d i a g r a m -5.0 knorthite Theoretical path • Upper Station X Lower Station Kaolinite • i • ! Quartz Saturation Line -4.5 -4.0 -3.5 log aH4Si04 -3.0 Figure 6.1. A c t i v i t i e s of stream water samples from the two monitoring s t a t i o n s p l o t t e d on a mineral s t a b i l i t y -diagram. 69 6.4.2 DISCUSSION The temporal v a r i a b i l i t y observable for the two stations i n figure 6.1 i s caused by d i l u t i o n of the base flow (data points move along the x-axis toward the gibbsite f i e l d ) and by an increased hydrogen ion concentration (motivate data to move upward along the y-axis). The s p a t i a l v a r i a b i l i t y between the stations i s limited. The data points for the upper basin depict, however, a more scattered pattern. A discrepancy between analyzed stream water data and calculated data was found (see figure 6.1). The inconsistency between actual data and theoreti c a l geochemical pathway may be caused by a number of li m i t a t i o n s i n the assumptions. These l i m i t a t i o n s can be summarized as: 1) Mass balance approach gave erroneous re s u l t s leading to f a u l t y i n i t i a l constraints. 2) Due to k i n e t i c barriers, equilibrium between natural waters and minerals i s not always achieved 3) The thermodynamic data base i s inconsistent. 4) Theoretical calculations were assuming closed system concerning carbon dioxide, which can lead to an underestimation -of hydrogen ions present. In spite of the many limi t a t i o n s of the thermodynamic approach i t i s reassuring to note that the f i e l d data do approximate 70 calculated data from the theoretical approach. If nothing else, the f i e l d data show that the assumption made i n the mass balance approach that k a o l i n i t e forms as a secondary mineral i n the stream i s correct. 6.5 SUMMARY Three approaches were used i n order to analyze the chemical c h a r a c t e r i s t i c s of the stream water; mass-balance, s t a t i s t i c a l and thermodynamic. The mass balance approach suggested that approximately 50% of the hydrochemical load originated from anorthite weathering. It further showed that close to 25% of the solutes came from pyrite and the remainder from a l b i t e , hornblende and K-feldspar i n order of importance. The high anorthite contribution of solutes agrees well with other mountain studies, but i s much higher than the proportion of anorthite i n the bedrock. Almost no temporal and s p a t i a l differences i n minerals contributing solutes were observed. The s t a t i s t i c a l approach showed that a small difference occurred between the a c t i v i t i e s of Na at the upper s i t e and K at the lower st a t i o n and that of other major ions, with increased discharge. The r e l a t i v e l y smaller d i l u t i o n of Na at the upper st a t i o n compared to that of other major ions at high flow could r e s u l t from incongruent weathering of the glass f r a c t i o n of volcanic ash. At the lower basin the smaller d i l u t i o n of K could be an e f f e c t of leaching of organic material during overland . 71 flow. The difference may be the resu l t of in response i s , however, an a l y t i c a l errors. so small that i t The s t a b i l i t y diagrams, using thermodynamic relationships, showed that the stream water.during event #3 was i n equilibrium with k a o l i n i t e . The temporal v a r i a b i l i t y v i s i b l e i n the s t a b i l i t y diagram i s caused mainly by d i l u t i o n during storm flow. Theoretical modelling using GEOL PATH and i n i t i a l constraints s i m i l a r to those derived from the mass balance approach approximate the f i e l d data. 72 CHAPTER 7 - CONCLUSIONS AND IDEAS FOR FUTURE RESEARCH Hydrograph separation of rain-driven storm flow into i t s storm and pre-storm components at the two study s i t e s depicted a much larger pre-storm water f r a c t i o n (60%-90%) than previously had been expected. Although most lowland studies using stable isotope separation have suggested a pre-storm water f r a c t i o n of up to 90% during p r e c i p i t a t i o n events i t was believed that the steep slopes i n combination with hydrophobic s o i l s and coarse talus material would produce a storm water controlled runoff hydrograph. The rapid i n f l u x of previously stored water i n the study basin during p r e c i p i t a t i o n events i s most l i k e l y caused by pressure propagation of water from the macropore system. In the hydrophobic soils'., water i s believed' to run off as overland flow u n t i l i t enters 'the subsurface environment. The displacement ef f e c t of water from the macropore system could be enhanced i n the subsurface environment by the heavily fractured bedrock i n the area acting as e f f i c i e n t hydrological conduits. The large pre-storm water component generates a r e l a t i v e l y long average residence of water i n the subsurface environment. This has important implications for the buffering of incoming ac i d r a i n water which i s mainly controlled by chemical weathering reactions i n the s o i l and bedrock systems. The acid buffering capacity of r a i n water i s noticeable i n the comparably small decrease i n stream water pH during the p r e c i p i t a t i o n events. The 73 buffering of acid i s further observed by the n e u t r a l i z a t i o n of the r e l a t i v e l y large production of acid due to the oxidation of p y r i t e i n the study area. Hence the study area i s not very susceptible to periodic a c i d i f i c a t i o n during rain-driven events. The study suggests that s i l i c a and EC can be used as a l t e r n a t i v e hydrological tracers under certain hydrological and l i t h o l o g i c a l conditions. These alternative tracers should, however, be v e r i f i e d against stable isotope tracers before use, as the conservative behavior depends on s p e c i f i c c h a r a c t e r i s t i c s of each basin. At the upper basin outlet both EC and s i l i c a underestimated the pre-storm contribution. This i s probably caused by the coarse talus slope intercepting much of the main stream i n the upper basin preventing equilibrium or steady state conditions to be reached. At the lower station s i l i c a and EC showed a s i m i l a r pattern to that of the. more conventional deuterium and oxygen-18 tracers. The calculated pre-storm component using EC was, however, 10%-20% lower than the calculated values from the other three tracers. The advantage of using these alternative tracers i s that hydrograph separation r e s u l t s can a p r i o r i be anticipated. A further advantage of using EC i s that i t can be continuously measured and stored i n dataloggers. In t h i s study i t was hypothesized that a s p a t i a l and temporal v a r i a b i l i t y i n the hydrochemistry between the two monitoring 74 s i t e s and during individual r a i n storms could be recognized. As the hydrochemical v a r i a b i l i t y i s a function of the average residence time of water i n the unique combination of hydrological reservoirs i n each basin i t was assumed that the int e r p r e t a t i o n of short hydrochemical fluxes could help i n the in t e r p r e t a t i o n of the v a r i a b i l i t y i n solute sources. The temporal v a r i a t i o n i n hydrochemistry of the two s i t e s was found to be mainly controlled by the input of d i l u t e event water. However, a marginal difference i n response was observed i n the a c t i v i t y of Na at the upper and K at the lower st a t i o n compared to other major ions at increasing discharge. The r e l a t i v e l y smaller decrease i n Na a c t i v i t y at high flow could res u l t from incongruent weathering of the glass f r a c t i o n of volcanic ash. For K a similar response could be caused by leaching of organic material during overland flow. The difference i n response for Na and K i s , however, so small that i t could be an effect of a n a l y t i c a l uncertainties. The s p a t i a l v a r i a t i o n between the two s i t e s i s mainly generated by the more d i l u t e character of the upper basin runoff. The more concentrated stream water at the lower basin i s probably caused, partly, by re-entering groundwater from the upper basin and p a r t l y also by longer average residence time and a more reactive subsurface environment motivated by a more s o i l covered and lush r i p a r i a n zone. 75 Due to the heterogeneity of the studied drainage basins i t i s d i f f i c u l t to quantify the contribution of water and solutes from the d i f f e r e n t hydrological reservoirs at a desirable scale. In order to achieve a more complete understanding of i n d i v i d u a l hydrological reservoirs contribution i t would be desirable to study more homogenous drainage basins i n order to increase the control over geomorphological and l i t h o l o g i c a l c h a r a c t e r i s t i c s . 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Water Resources 85 Research, Vol. 24, No. 10, pg. 1645-1650. Zeman, L. J. and E. O. Nyborg, (1974). C o l l e c t i o n of chemical f a l l o u t from the atmosphere. Canadian Agriculture Engineering, Vol 16, No. 2, pg. 69-72. Zeman, L. J. and H. O. Slaymaker, (1975) . Hydrochemical analysis to discriminate variable runoff source areas i n an alpine basin, A r c t i c and Alpine Research, Vol. 7, No. 4, pg. 341-351. 86 Appendix I. A c t i v i t i e s of stream and p r e c i p i t a t i o n samples SAMPLE DATE TIME aK+ aNa+ aCa2+ aMg2+ aH4Si04 a S 0 4 2 - a H C 0 3 - PH Charge (M) (M) (M) (M) (M) (M) (M) balance% P1 6/9 12.00 7.67E-07 3.88E-06 3.46E-06 7.93E-07 B.D. 2.64E-05 B.D. 4.85 -31.8 P2 9/9 14.00 B.D. 3.02E-06 9.90E-07 1.59E-06 B.D. 2.19E-05 B.D. 5.04 -43.4 P3 18/9 14.10 2.30E-06 4.31 E-06 9.89E-07 7.94E-07 B.D. 2.69E-05 B.D. 5.32 -56.5 P6 6/10 19.00 2.30E-06 1.21 E-05 9.89E-07 7.92E-07 B.D. 2.81 E-05 B.D. 5.06 -35.7 SAMPLE DATE TIME aK+ aNa+ aCa2 + aMg2+ aH4Si04 a S 0 4 2 - a H C 0 3 - PH Charge (M) (M) (M) (M) (M) (M) (M) balance% B4 2/9 10.20 1.10E-05 3.56E-05 1.18E-04 1.29E-05 1.08E-04 5.59E-05 2.19E-04 7.37 -3.6 B6 4/9 14.30 1.22E-05 3.77E-05 1.22E-04 1.37E-05 1.13E-04 5.46E-05 2.11 E-04 7.32 0.3 B7 6/9 11.00 1.10E-05 3.56E-05 1.14E-04 1.33E-05 1.06E-04 5.16E-05 2.03E-04 7.31 -0.8 B9 7/9 21.00 1.02E-05 3.23E-05 9.85E-05 1.16E-05 9.15E-05 4.93E-05 1.79E-04 7.28 -2.7 B10 7/9 23.00 7.51 E-06 2.72E-05 7.51 E-05 8.30E-06 6.73E-05 3.85E-05 1.39E-04 7.18 -3.4 B11 8/9 03.00 1.07E-05 4.42E-05 8.03E-05 9.38E-06 6.98E-05 4.26E-05 1.63E-04 7.10 -2.8 B12 8/9 07.00 8.26E-06 2.85E-05 7.39E-05 8.68E-06 6.44E-05 3.32E-05 1.55E-04 7.03 -4.6 B13 .8/9 11.00 7.02E-06 2.47E-05 6.74E-05 7.97E-06 6.27E-05 3.20E-05 1.22E-04 7.06 -1.0 B15 8/9 19.00 7.51 E-06 2.64E-05 7.39E-05 8.30E-06 7.01 E-05 3.95 E-05 1.39E-04 7.18 -4.6 B16 8/9 23.00 9.01 E-06 2.64E-05 7.81 E-05 9.04 E-06 7.26E-05 3.79 E-05 1.55E-04 7.02 -4.7 B17 9/9 03.00 7.51 E-06 2.55E-05 7.85E-05 9.06E-06 7.51 E-05 3.29E-05 1.47E-04 7.09 -1.0 B19 9/9 13.00 9.98E-06 3.31 E-05 9.82E-05 1.19E-05 9.44E-05 4.93E-05 2.03 E-04 7.22 -6.8 SAMPLE DATE TIME aK+ aNa+ aCa2 + aMg2 + aH4Si04 a S 0 4 2 - a H C 0 3 - pH Charge (M) (M) (M) (M) (M) (M) (M) balance% A5 4/9 15.30 1.29E-05 4.10E-05 1.31 E-04 1.43E-05 1.05E-04 6.56E-05 2.10E-04 7.48 0.3 A7 6/9 12.45 1.24E-05 3.93E-05 1.27E-04 1.36E-05 1.05E-04 6.62E-05 2.11 E-04 7.66 -1.5 A8 7/9 16.00 1.34E-05 3.98E-05 1.29E-04 1.36E-05 1.06E-04 6.19E-05 2.11 E-04 7.24 0.6 A9 ' 7/9 20.15 1.27E-05 3.69E-05 1.11E-04 1.19E-05 9.76E-05 5.86E-05 1.95E-04 7.09 -2.7 A10 7/9 23.15 1 32E-05 3.47E-05 1.24E-04 1.29 E-05 9.76E-05 5.61 E-05 2.11 E-04 7.02 -0.3 A11 8/9 01.15 1.07E-05 3.22E-05 1.01 E-04 1.15E-05 9.08E-05 5.42E-05 1.87E-04 6.99 ^1.9 A12 8/9 03.15 1.07E-05 3.27E-05 1.04 E-04 1.15E-05 8.65E-05 5.23E-05 1.79 E-04 6.96 -1.7 A13 8/9 05.15 1 .05 E-05 3.18E-05 1.01 E-04 1.12E-05 8.40E-05 5.01 E-05 1.71 E-04 6.96 -0.8 A14 8/9 07.15 1 .02 E-05 2.97E-05 9.62E-05 1.05 E-05 8.08E-05 4.96E-05 1.63 E-04 6.96 -1.6 A15 8/9 09.15 8.74E-06 2.85 E-05 8.75E-05 9.74E-06 7.76E-05 4.93E-05 1.46E-04 6.96 -2.8 A17 8/9 13.15 8.99E-06 2.89 E-05 8.92E-05 9.36E-06 8.15E-05 5.01 E-05 1.46E-04 7.04 -2.4 A18 8/9 15.15 8.49E-06 2.80E-05 9.02E-05 9.74 E-06 8.12E-05 4.75E-05 1.46E-04 7.08 -1.0 A21 9/9 03.15 9.97E-06 3.22E-05 1.07E-04 1.11 E-05 9.01 E-05 5.42E-05 1.87E-04 6.98 -2.8 A22 9/9 07.15 9.73E-06 3.22E-05 1.05E-04 1.19E-05 9.22E-05 5.21 E-05 1.79 E-04 7.00 -1.3 A23 9/9 13.15 1.05E-05 3.52E-05 1.12E-04 1.26E-05 9.22E-05 5.68E-05 1.87E-04 7.19 -0.9 A24 9/9 19.10 1.32E-05 3.89 E-05 1.28E-04 1.40E-05 1.01 E-04 6.20E-05 2.02E-04 7.12 1.3 B.D. = below detection limit 87 Appendix II. Hydrograph separation using D and Precipitation samples S A M P L E Date Time mm Deterium Oxygen-18 P2 (3) 8/9 07.30 1.5 -70 -10.1 P3(1) 8/9 1 8.10 21.2 -74 -10.4 P4 (2) 8/9 18.20 21.4 -70 -10.5 P5 (3) 8/9 18.30 20.8 -71 -10.7 P6(3) 9/9 13.00 3.4 -81 -11.8 Stream water samples from upper station S A M P L E Date Time Qt Deterium Oxygen-18 Qp (det) Qp (ox) Qp (avg) B5 3/9 12.30 1.95 -126 -16.9 1.92 1.89 1.90 B6 4/9 14.30 2.08 -126 -17.4 2.05 2.18 2.11 B7 6/9 11.00 1.95 -129 -17.0 2.01 1.93 1.97 B8 7/9 18.50 3.03 -124 -17.0 2.87 2.98 2.93 B9 7/9 21.00 4.41 -121 -16.6 3.94 4.07 4.01 B10 7/9 23.00 4.74 -117 -16.1 3.89 4.02 . 3.96 B11 8/9 03.00 5.09 -114 -16.1 3.90 4.32 4.11 B12 8/9 07.00 . 5.21 -112 -15.8 3.81 4.18 3.99 B13 8/9 11.00 6.50 -110 -15.4 4.51 4.82 4.66 B14 8/9 15.00 4.86 -109 -15.3 3.28 3.52 3.40 B15 8/9 19.00 3.88 -114 -15.8 . 2.97 3.11 3.04 B16 8/9 23.00 3.49 -114 -15.8 2.67 2.80 2.73 B17 9/9 03.00 3.39 -115 -16.0 2.66 2.82 2.74 B18 9/9 07.00 2.69 -119 -16.1 2.31 2.28 2.29 B19 9/9 13.00 2.45 -119 -16.6 2.10 2.27 2.18 B20 9/9 19.00 2.38 -112 -16.6 1.73 2.19 1.96 Stream water samples from lower station A6 3/9 13.00 4.24 A5 4/9 15.30 4.48 A8 7/9 16.00 4.36 A9 7/9 20.15 8.12 A10 7/9 23.15 9.86 A11 8/9 01.15 10.48 A12 8/9 03.15 10.70 A13 8/9 05.15 12.28 A14 8/9 07.15 10.91 A15 8/9 09.15 11.58 A16 8/9 11.15 13.00 A17 8/9 13.15 12.04 A18 8/9 15.15 9.86 A19 8/9 19.15 7.94 A20 8/9 23.15 7.42 A21 9/9 03.15 7.08 A22 9/9 07.15 5.83 A23 9/9 13.15 5.00 A24 9/9 19.10 5.00 -122 -17.0 4.08 , 4.18 4.13 -121 -17.3 4.23 4.62 4.42 -129 -17.0 4.77 4.29 4.53 -122 -16.6 7.82 7.50 7.66 -116 ' -16.3 8.35 8.65 8.50 -120 -16.1 9.69 8.88 9.28 -116 -15.9 9.06 8.74 8.90 -113 -15.6 9.69 9.46 9.58 -111 -15.6 8.10 8.41 8.25 -102 -15.3 6.70 8.40 7.55 -109 -15.4 9.27 9.62 9.44 -111 -15.3 9.05 8.73 8.89 -112 -15.4 7.59 7.30 7.45 -109 -15.5 5.66 6.00 4.62 -107 -15.7 5.00 5.83 4.41 -110 -16.0 5.18 5.89 5.54 -117 -16.1 5.05 4.94 5.00 -123 -16.3 4.90 4.39 4.64 -122 -16.6 4.81 4.61 4.71 88 Appendix I I I . Hydrograph separation using s i l i c a . Stream water samples from upper station SAMPLE Date Time Qt Si (M) Qp (Si) B4 2/9 10.20 2.15 1.08E-04 2.13 B6 4/9 14.30 2.08 1.13E-04 2.16 B7 6/9 11.00 1.95 1.06E-04 1.89 B9 7/9 21.00 4.41 9.15E-05 3.70 B10 7/9 23.00 4.74 6.73E-05 2.93 B11 8/9 03.00 5.09 6.98E-05 3.26 B12 8/9 07.00 5.21 6.44E-05 3.08 B13 8/9 11.00 6.50 6.27E-05 3.74 B15 8/9 19.00 3.88 7.01 E-05 2.50 B16 8/9 23.00 3.49 7.26E-05 2.32 B17 9/9 03.00 3.39 7.51 E-05 2.34 B19 9/9 13.00 2.45 9.44E-05 2.12 Stream water samples from lower station A5 4/9 15.30 4.48 1.05E-04 4.47 A7 6/9 12.45 4.24 1.05E-04 4.23 A8 7/9 16.00 4.36 1.06E-04 4.38 A9 7/9 20.15 8.12 9.76E-05 7.53 A10 7/9 23.15 9.86 9.76E-05 9.13 A11 8/9. 01.15 10.48 9.08E-05 9.04 A12 8/9 03.15 10.70 8.65E-05 8.79 A13 8/9 05.15 12.28 8.40E-05 9.80 A14 8/9 07.15 10.91 8.08E-05 8.38 A15 8/9 09.15 11.58 7.76E-05 8.54 A17 8/9 13.15 12.04 8.15E-05 9.33 A18 8/9 15.15 9.86 8.12E-05 7.60 A21 9/9 03.15 7.08 9.01 E-05 6.06 A22 9/9 07.15 5.83 9.22E-05 5.11 A23 9/9 13.15 5.00 9.22E-05 4.38 A24 9/9 19.10 5.00 1.01 E-04 4.78 Silica in precipitation was below detection limit 89 Appendix IV. Hydrograph separation using EC. Stream water sample from upper station SAMPLE Date Time Qt EC Qp (EC) B8 7/9 18.50 3.03 0.0211 3.05 B9 7/9 21.00 4.41 0.0197 4.02 B10 7/9 23.00 4.74 0.0141 2.55 B11 8/9 03.00 5.09 0.0142 2.76 B12 8/9 07.00 5.21 0.0121 2.09 B13 8/9 11.00 6.50 0.0120 2.58 B14 8/9 15.00 4.86 0.0101 1.30 B15 8/9 19.00 3.88 0.0121 1.55 B16 8/9 23.00 3.49 0.0130 1.60 B17 9/9 03.00 3.39 0.0123 1.40 B18 9/9 07.00 2.69 0.0164 1.85 B19 9/9 13.00 2.45 0.0180 1.95 Stream water sample from lower station A5 4/9 15.30 4.48 0.0401 4.58 A7 6/9 12.45 4.24 0.0394 4.24 A8 7/9 16.00 4.36 0.0391 4.33 A9 7/9 20.15 8.12 0.0371 7.55 A10 7/9 23.15 9.86 0.0325 7.82 A11 8/9 01.15 10.48 0.0310 7.85 A12 8/9 03.15 10.70 0.0294 7.47 A13 8/9 05.15 12.28 0.0281 8.10 A14 8/9 07.15 10.91 0.0268 6.78 A15 8/9 09.15 11.58 0.0255 6.74 A16 8/9 11.15 13.00 0.0262 7.83 A17 8/9 13.15 12.04 0.0250 6.81 A18 8/9 15.15 9.86 0.0251 5.62 A19 8/9 19.15 7.94 0.0284 5.31 A20 8/9 23.15 7.42 0.0299 5.29 A21 9/9 03.15 7.08 0.0305 5.20 A22 9/9 07.15 5.83 0.0306 4.30 A23 9/9 13.15. 5.00 0.0332 4.06 A24 9/9 19.10 5.00 0.0367 4.59 90 Appendix V. Mass balance calcu l a t i o n s . Proportion of minerals contributing to upper station hydrochemistry Residuals in % subtract H+ rain H+ pyr SAMPLE Anorthite Albite K-spar Hornblend Pyrite Si H C 0 3 - H C 0 3 - H C 0 3 -B4 0.48 0.13 0.05 0.10 0.24 21.98 -35.02 -30.85 20.25 B6 0.49 0.13 0.05 0.10 0.23 19.44 -46.91 -42.58 9.24 B7 0.48 0.13 0.05 0.11 0.23 • 20.44 -42.45 -37.95 12.93 B8 0.45 0.15 0.05 0.10 0.25 ' < 6.89 -43.77 -38.15 21.29 B9 0.47 0.14 0.05 0.10 0.24 17.53 -40.17 -35.06 20.14 B10 0.46 0.15 0.05 0.10 0.25 13.00 -36.64 -30.06 25.51 B11 0.41 0.22 0.06 0.09 0.23 -42.49 -36.54 -30.95 21.39 B12 0.46 0.16 0.05 0.10 0.22 2.58 -22.62 -16.75 26.19 B13 0.46 0.15 0.05 0.10 0.23 16.43 -39.14 -31.71 20.56 B15 0.45 0.15 0.05 0.10 0.25 18.96 -34.38 -27.80 29.26 B16 0.46 0.14 0.06 0.10 0.24 17.20 -27.63 -21.76 27.25 B17 0.49 0.14 0.05 0.11 0.21 26.15 -33.60 -27.39 17.53 B19 0.46 0.14 0.05 0.11 0.24 18.61 -23.67 -19.18 29.38 Proportion of minerals contributing to lower station hydrochemistry A5 0.47 0.13 0.05 0.10 0.25 5.12 -57.60 -53.26 9.09 A7 0.47 0.13 0.05 0.09 0.26 9.57 ' -52.36 -48.00 14.94 A8 0.48 0.13 0.05 0.10 0.24 7.49 -54.77 -50.44 8.39 A9 0.46 0.14 0.05 0.09 0.25 7.99 -45.61 -40.93 19.26 A10 0.49 0.12 0.05 0.10 0.23 10.89 -46.52 -42.21 11.05 A11 0.46 0.13 0.05 0.10 0.26 15.84 -36.80 -31.94 26.11 A12 0.47 0.13 0.05 0.10 0.25 10.70 -46.31 ^11.23 17.30 A13 0.47 0.13 0.05 0.10 0.24 10.81 -48.94 -43.62 15.08 A14 0.47 0.13 0.05 0.10 0.25 13.50 -48.36 -42.78 18.23 A15 0.46 0.13 0.05 0.10 0.27 17.39 -49.90 -43.71 23.59 A17 0.46 0.13 0.05 0.09 0.27 19.93 -52.27 -46.06 22.43 A18 0.47 0.13 0.05 0.10 0.26 22.69 -53.14 -46.93 17.96 A21 0.48 0.13 0.05 0.09 0.25 17.07 -42.88 -38.02 20.07 A22 0.47 0.13 0.05 0.10 0.25 19.13 -47.42 -42.34 16.00 A23 0.47 0.13 0.05 0.10 0.25 10.81 -51.41 -46.53 14.32 A24 0.48 0.13 0.05 0.10 0.24 4.90 -59.53 -55.03 6.26 91 

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