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DETERMINATION OF SOURCES AND FLOWPATHS USING ISOTOPIC AND CHEMICAL TRACERS, GREEN LAKES VALLEY, ROCKY MOUNTAINS. Fengjing Liu and Mark Williams Department of Geography and Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO80309. HYDROLOGIC FLOWPATHS.
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DETERMINATION OF SOURCES AND FLOWPATHS USING ISOTOPIC AND CHEMICAL TRACERS, GREEN LAKES VALLEY, ROCKY MOUNTAINS Fengjing Liu and Mark Williams Department of Geography and Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO80309
HYDROLOGIC FLOWPATHS • Generally, 4 paths • Change over time • Change over space
OBJECTIVES • understanding the mechanism of stream flow generation in snow-dominated alpine basins • determining uncertainties of hydrograph separation by using different mixing models and tracers
RESEARCH SITE AND SAMPLE COLLECTION • Stream water - weekly grab samples • Snowmelt - snow lysimeter • Soil solution - zero tension lysimeter Delta 18O, DOC, Solutes
MASS BALANCE MODEL FOR WATER SOURCES AND FLOWPATHS Ci1Q1 + Ci2Q2 + Ci3Q3 + .. + CinQn = CitQt Q1 + Q2 + Q3 + .. + Qn = Qt C - tracer concentrations Q - discharge (runoff) i - tracers n - water source or flow path components t - stream flow How we use 2 to 4 component mixing model
End-Member Mixing Analysis (EMMA) and PCA • Tracer concentrations distinct - time series plots • Tracers conservative - mixing diagram • Number of components - PCA • Qualification of end-member characterization • EMMA solutions for hydrograph separation
SOURCE WATER SEPARATION- 2 COMPONENTS Martnelli GL4 Calendar Day (1996)
RESULTS FOR FLOW SOURCES GL4 Martinelli Calendar Day (1996)
FLOWPATH SEPARATION - QUALIFICATION OF 2C SEPARATION • Na+, Si, SO42-, and K/Si are conservative at both catchments • 2-component flowpath separations using Na+, Si, SO42- are not successful in that characterization of the subsurface is difficult • Concentrations of those tracers vary a lot over soil horizons
FLOWPATH SEPARATION - K/Si Overland vs. subsurface flow GL4 Calendar Day (1996)
FLOWPATH SEPARATION - DOC Upper soil horizon vs. deeper flow GL4
FLOWPATH SEPARATION - 4 COMPONENTS Martinelli 2/16/77/5 GL4 2/25/39/34
EMMA PCA Diagram Martinelli GL4
4-C SEPARATION - EMMA SOLUTIONS Martinelli GL4 Methods 3-Tracers (18O,K/Si,DOC) Least square optimization (Na,Si,SO4,K/Si,18O,DOC) PCA Projection (U) (Na,Si,SO4,K/Si,18O,DOC)
SUMMARY • New water accounts for 95% at Mart, while new water decreases to 65% at GL4 • K/Si and DOC are efficient tracers to identify overland and upper soil horizon flow • 3-tracer-4-component separation is superior to EMMA approach • Four flowpaths are successfully identified: overland, upper soil horizon, lower soil horizon, and base flow (2/16/77/5 at Mart; 2/25/39/34 at GL4)