Linking Hydrologic Exchange to Nitrogen Cycling at the Groundwater-Stream Water Interface

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JACKMAN, TRISKA, and DUFF The interface between ground water and surface water is a dynamic boundary where strong gradients in nutrients, dissolved oxygen, and redox potential occur. This interface zone, termed the hyporheic zone, exerts considerable influence on the biotic communities of streams and rivers, the flux of nutrients from terrestrial to aquatic ecosystems, and upon the hydrology of streams, rivers, and floodplains. This project focuses upon this dynamic interface with emphases on the cycling of nitrogen and effects on aquatic macrophytes. The project combines a thorough study of hydrology of the hyporheic zone with the biogeochemistry and biological interactions at this interface. This research will yield significant progress in coupling the hydrology and biogeochemistry of catchments at the terrestrial/aquatic interface. Riparian zones have been shown to provide buffering capacity for reducing the import of excessive nutrients of terrestrial origin into aquatic ecosystems. These initial studies on this filtering capacity of this interface, however, have not been coupled to a rigorous characterization of the hydrologic flow paths in space and time within this zone. This project quantifies major components of nitrogen cycling along known flow paths and follows the impact of these processes to the biota of stream and river ecosystems.