This project focuses on the role of soil-stream interfaces as control-points for the speciation (NO3-vs. NO2-vs. NH4+vs. DON vs. N2O) and flux of N in a heterogeneous landscape. Biogeochemical transformations of N at the soil-stream interface may have important effects on both the quantity and quality (speciation) of N lost to downstream ecosystems, and may modify the extent to which h the chemistry of watershed streams are affected by watershed processes. A mechanistic understanding of such N transformations along soil-stream flowpaths may therefore be critical in order to predict how watershed disturbances (both short-term and chronic) will affect surface-water chemistry. Preliminary studies from the Augusta Creek Watershed have pointed to soil-stream interfaces as potential control-points for downstream speciation and flux of N. The work outlined in this project seeks to provide an understanding of rates and mechanisms of N transformations along explicit soil-stream hydrologic flowpaths in the watershed. The principal investigators will use both descriptive and experimental approaches, including the use of tracers of hydrologic flowpaths (LiBr) and tracers for specific biogeochemical reactions (stable N isotopes). The main goal is to understand how patterns of N transformations at soil-stream interfaces vary in space, time,and as a function of hydrology.
