TRANSPORT, TRANSFORMATION, AND RETENTION OF ARSENIC IN A HEADWATER STREAM

We are using combination of hydrologic studies of ground water-surface water exchange, geochemical investigations of the interaction between dissolved and solid components, and experimental studies of the influence of biological processes to elucidate the processes that govern arsenic cycling in a stream-aquifer system. This interdisciplinary project involves four main elements. The first element involves characterization the extent of the alluvial aquifer, its hydrogeochemistry, and how sources of arsenic to the stream may vary with time and space. The second element aims to characterize the extent of the hyporheic zone through application of tracer injections and solute transport models. By adding a reactive uptake term to our models, we will characterize the hyporheic zone as either a “sink” or “source” of arsenic and generate measures of uptake that may be compared to more specific studies of biological activity. The third element focuses on the important interactions between arsenic and solid phases in the streambed, the hyporheic zone, and the aquifer. The fourth element addresses whole-system and microcosm studies that rely on techniques developed by stream ecologists to tie biological activity to the uptake and transformation of arsenic by different biological compartments. Results of this interdisciplinary research will have implications for our general understanding of the biogeochemical cycling of redox-sensitive trace elements such as arsenic in both natural and human-impacted systems.