Alpine biogeochemical modeling: Case studies, improvements, and parameter estimation

The geochemical, biogeochemical, and hydrologic controls on the stream chemical composition of alpine watersheds were investigated using the Alpine Hydrochemical Model (AHM). This model was successfully applied to the Emerald Lake watershed and two nearby watersheds as well as two watersheds in the Rocky Mountains, Andrews Creek and the Green Lakes Valley. The results reveal that snowmelt in alpine watersheds must come into contact with either soil, sub-talus, or reactive bedrock surfaces to explain the geochemistry observed in alpine lakes and streams. These materials do not differ geochemically but they do differ in their influence on the amount of mineral nitrogen observed in alpine lakes and streams. Improvements to the carbon-nitrogen dynamics portion of the AHM indicate that the Emerald Lake watershed is nearing nitrogen saturation. A robust multi-criteria sensitivity analysis technique was used to determine what processes were important for simulating the observed stream chemical composition. This sensitivity analysis revealed that concentration and mass flux representations of stream chemical composition contain different information about the watershed. The sensitivity analysis results were used to guide a multi-criteria parameter estimation algorithm. The results showed that stream chemical data is useful in discerning the importance of different processes and the role they play in determining stream chemical composition.