Hydrochemical response of alpine watersheds to snowmelt.

This study explores the stream hydrochemical response to snowmelt in alpine environments in the context of variable source area (VSA) dynamics and nitrate. Green Lakes Valley, CO (GLV) and Tokapah Basin, CA (TOK) are two geologically and climatologically different alpine watersheds that served as our study sites for hydrochemistry comparisons (focused on nitrate, NO3-) over a 12 year period (1996-2007).  We used a three-part approach involving a seasonal nitrate balance, hydrochemical flushing behavior analysis, and correlation between the spatiotemporal distribution of snowmelt and stream nitrate concentration. Generally, GLV exhibited high levels of N-export (i.e. greater stream N-export than snowpack N-loading) for all years; in TOK, years with a greater snowpack exhibited N-export, and years with a smaller snowpack exhibited N-retention. In GLV, the residuals of catchment N-flushing behavior were proportional to the basin N-flushing time, suggesting the importance of VSA dynamics for the basin’s hydrochemistry. Additionally, the contributing (snowmelt) area of the basin was better correlated with the stream nitrate concentration in TOK than in GLV (greater significant r² values). These results suggest that GLV may be potentially less sensitive to snowpack N-loading and snowmelt than “classic” alpine basins such as TOK. As the snowpack regimes of these alpine catchments are altered by climate change and N-loading to these areas increases over the next century, it will become increasingly important to understand how these sensitive catchments may react chemically, hydrologically, and ecologically.