SURFACE-GROUNDWATER INTERACTIONS AND NUTRIENT TRANSPORT IN ALPINE VS SUBALPINE CATCHMENTS, FRONT RANGE, CO

Here we compare nutrient fluxes from two high elevation catchments, Como Creek and the Green Lakes Valley. These watersheds are similar in climate, aspect, and geography, but differ in landscape type. Como Creek primarily drains subalpine forest with little alpine area. In contrast, the adjacent Green Lakes Valley drains alpine tundra and talus slopes, before reaching our sampling location in a subalpine forest. Using NH4+, NO3-, DON, and DOC yields from Como Creek and the Green Lakes Valley from the last 10 years, we find that alpine areas subsidize transport of inorganic nitrogen down gradient into forested areas. In contrast, at Como Creek there is little export of inorganic N, higher export of organic N, and much greater export of DOC compared to Green Lakes Valley. Hydrologic mixing models using O18 as a tracer from snow, snowmelt lysimeters, wells, and streams show that discharge at Como Creek is characterized by a well-mixed groundwater reservoir with a residence time of years to decades, whereas the Green Lakes Valley discharge shows more recent water characterized by shallow subsurface flow.