SS2.02 Biogeochemical Process at the Sediment-Water Interfaces
Date: Tuesday, June 11, 2002
Time: 9:30:00 AM
Location: Carson B
 
HarveyJW, U.S. Geological Survey, Reston, USA, jwharvey@usgs.gov
 
RECENT ADVANCES IN CHARACTERIZING HYPORHEIC FLOW AND ENHANCED BIOGEOCHEMICAL REACTIONS IN STREAMS AND RIVERS
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In many aquatic environments the exchange of solutes across sediment boundaries is not limited by diffusion. Advective fluxes into and out of sediment are usually involved except where sediments are very fine and overlying water very still. In streams these advective fluxes are called 'hyporheic exchange'. The increased delivery of streamwater to the subsurface and greater contact area with sediment is thought to enhance a variety of biogeochemical reactions, including oxidation of metals, nitrification and denitrification, and degradation of organic compounds. Modelers have generally been restricted to working with data collected in flumes, in part because of the difficulty of measuring vertical profiles of reactive solutes and solute tracers in the field at appropriate spatial and temporal scales. Here the use of low volume pumping of water samples from the streambed, combined with a solute tracer release, is demonstrated as a superior means to characterize biogeochemical reactions at the fine spatial scales of individual hyporheic flow paths. Examples are presented from a desert stream affected by metal-mining operations, and from a midwestern stream affected by input of agricultural nitrogen.