The goal of this project is to develop a detailed understanding of the hydrology of hyporheic zones and to interface chemical and microbial processes occurring within hyporheic zones to the hydrologic dynamics of these environments. The specific objectives of this project are: 1. Develop and validate a numerical model coupling hyporheic groundwater flow and open-channel flow. 2. Install hydrologic monitoring networks in three catchments with differing parent lithologies to obtain uninterrupted measurements of the hydrology of the hyporheic zones and surface waters. These data will be used to test and validate the numerical models. 3. Perform tracer experiments to further validate the general applicability of the coupled flow/transport model. 4. Examine the interactions between hyporheic zone hydrology and microbial processes with regards to dissolved oxygen availability, the form and amount of inorganic nutrients, and the cycling of carbon. 5. Evaluate the role of the hyporheic zone on microbial photosynthesis and chemosynthesis at the sediment/water interface. Drs. Dahm and Campana are outstanding stream researchers. This project couples stream hydrology with the chemical and biological processes that occur within the hyporheic zone. The facilities available for this research are outstanding. //