HR: 15:25h
AN: H23J-08    [Abstracts]
TI: The Streambed as a Dynamic Membrane in the Watershed
AU: * Constantz, J
EM: jconstan@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd. MS-496, Menlo Park, CA 94025,
AB: Improved understanding of the streambed filtering capacity is essential for predicting and mitigating anthropogenic impacts on stream and ground-water quality. This presentation discusses the extent and composition of the streambed, and introduces the concept of the streambed as a dynamic membrane, periodically changing character while continually filtering water flowing through its matrix. The physical extent of a streambed is described as sediments in the watershed under direct influence of an active stream, often forming over paleo streambeds and overbank materials comprising the alluvial aquifer, but also forming thin layers on bedrock in upland locations. The active streambed may consist of a single particle size, such as fine sand, or consist of a wide range of particle sizes of both inorganic and organic material. In alluvial settings, the streambed is often similar in general thickness and porosity to adjacent soils. The initial streambed filtering capacity is controlled by the particle-size characteristics of both the bulk properties and the stratigraphic layering of the matrix, and supplemented by a microbiological and invertebrate community that rapidly populates the matrix to complete the composition of streambed. Once a biogeochemical streambed matrix is established within an alluvial system, the quality of water passing through the streambed is transformed, such that stream and ground- water quality are distinct in their chemical and microbial composition. The physical matrix, geochemistry, and the resident biology may change seasonally (due to scour, deposition, and changing hydraulic, chemical, and thermal boundary conditions), such that streambed properties are temporally dynamic. Thus, as a system- regulated filter, the streambed may be viewed as a dynamic membrane, which facilitates engagement of membrane science for characterizing the streambed filtering capacity.
DE: 1830 Groundwater/surface water interaction
DE: 1860 Streamflow
DE: 1879 Watershed
SC: Hydrology [H]
MN: 2007 Fall Meeting