Singley, Joel G 1 ; Wlostowski, Adam N 2 ; Bergstrom, Anna J 3 ; Sokol, Erick R 4 ; Torrens, Christa L 5 ; Jaros, Chris 6 ; Wilson, Colleen E 7 ; Gooseff, Michael N 8
1 Environmental Studies Program, University of Colorado Boulder
2 Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder
3 Department of Geological Sciences, University of Colorado Boulder
4 Institute of Arctic and Alpine Research, University of Colorado Boulder
5 Environmental Studies Program, University of Colorado Boulder
6 Institute of Arctic and Alpine Research, University of Colorado Boulder
7 Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder
8 Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder
The analysis of concentration-discharge (C-Q) relationships has often been used in an inverse modeling framework to quantify source water contributions and biogeochemical processes occurring within catchments, especially during discrete hydrological events. Yet, the interpretation of C-Q hysteresis is often confounded by catchment complexity, such as a large number of source waters and non-stationarity in their hydrochemical composition. Attempts to overcome these challenges often necessitate ignoring or lumping together potentially important runoff pathways and geochemical sources/sinks. This is especially true of the hyporheic zone because it acts as an integrator of multiple sources and typically lacks a unique hydrochemical signature. Furthermore, these complexities often limit efforts to identify catchment processes responsible for the transience of C-Q hysteresis between discrete hydrological events. To address these challenges, we leverage the hydrologic simplicity and long-term, high frequency Q and electrical conductivity (EC) data from streams in the McMurdo Dry Valleys, Antarctica. In this two end-member system, EC can serve as a proxy for the concentration of solutes derived from the hyporheic zone and reveal the legacy of mixing processes occurring along the stream. We utilize a novel approach to decompose loops into sub-hysteretic EC-Q dynamics in order to identify individual mechanisms governing hysteretic patterns and transience across a wide range of timescales. From this analysis, we find that hydrologic and hydraulic processes govern EC response to diel and seasonal Q variability resulting in discrete hysteretic behavior. We also observe that variable hyporheic turnover rates govern EC-Q patterns at daily, annual, and interannual timescales and contribute differently to transient hysteresis in short and long streams. The framework we utilize to analyze sub-hysteretic dynamics may be applied more broadly to constrain the processes controlling C-Q transience and aid advancements in understanding the evolution of catchment processes and structure over time.