Streams are complex three-dimensional ecosystems in which surface and ground water components are interaction the interface between the surface and subsurface affects the transfer of water and solutes between the stream and ground water and varies in response to variable climate. The main objectives of this research project are to quantify the sources and flow dynamics of water at the ground water/surface water ecotone of headwater streams and to determine biogeochemical and ecological responses resulting from these interactions. Three objectives are central. First, the hydrology of the ground water/surface water ecotone will be determined. Three montane catchments with different alluvial sediment types (fine-grained to coarse cobble) will be instrumented. Hydrologic models that characterize surface transport and exchange with the subsurface (OTIS), three-dimensional flow dynamics within the ground water ecotone (MODFLOW), and hillslope routing of water from the upslope to the stream (TOPMODEL) will be used. These models will be used to describe the transient hydrologic nature of headwater catchments and to quantify the temporal variation in ground water/ surface water exchange. Seco nd, the three-dimensional biogeochemical structure of the ecotone will be investigated. They will describe the vertical distribution of biogeochemical processes in downwelling (ground water rechange) and upwelling (ground water discharge) reaches of streams. In addition, the will determine whether flooding or drying will relocate many microbial processes. Third, they will measure the response of biotic communities to variation in the hydrologic exchange. Specifically, studies will be undertaken to assess the community structure and biomass of benthic algal assemblages, rates of primary production and respiration, and controls on algal community structure and succession in the stream-aquifer interface. The ecotone between surface waters and ground waters is extremely important. The terrestrial portion, the riparian zone is crucial to improving water quality and wildlife habitat. The aquatic component includes a dynamic subsurface that regulates nutrient content and cycling. ve. T varies in response to and discharge verying 1996.
