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Ecology

Biogeochemical Processes and Microbial Characteristics Across GroundWater - Surface Water Interfaces

We evaluated the freeze-core and passive multilevel sampler (MLS) methods for collecting samples suitable for microbiological and geochemical analyses from the ground water-surface water mixing zones of large, cobble-bed rivers. The development of effective methods for collecting samples from the ground water-surface water interaction zone will allow researchers to investigate (1) how microbial communities within the mixing zones are affected by hydrologic and geochemical processes occurring at ground water – surface water boundaries, and (2) how microbial communities may affect contaminant transport, and ultimately fate and effects, across ground water - surface water boundaries. In FY 00 and 01 we used freeze core samples to determine that significant populations of viable bacteria, including a range of anaerobic microorganisms, are ubiquitous in Columbia River sediments. We demonstrated that the indigenous microbiota could reduce chromate to a non-soluble species, probably Cr(III). In FY 02 we used passive multilevel samplers to measure fine-scale geochemical variation in the hyporheic zone. We measured chemical gradients between surface water and groundwater for dissolved nutrient anions, organic and inorganic carbon, and contaminant chromate. These measurements were made for samples collected relative to diurnal fluctuations in ambient hydraulic head (e.g., high and low river stage). River stage fluctuations and water pressure changes in the hyporheic zone were used to determine the vertical hydraulic gradient (VHG), which indicated net water movement either down from the river into the hyporheic zone or up from the hyporheic zone into the river. This information can be used to more accurately predict the transport, fate, and effect on surface water biota of contaminants traveling through the hyporheic zone.

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  • Moser DP, JK Fredrickson, DR Geist, EV Arntzen, AD Peacock, SW Li, CM Spadoni, and JP McKinley. 2003. "Biogeochemical Processes and Microbial Characteristics Across Groundwater - Surface Water Boundaries of the Hanford Reach of the Columbia River." Environmental Science and Technology 37(22):5127-5134.

Ecology

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