HR: 0800h
AN: H41C-0654    [Abstracts]
TI: Improving Managed Aquifer Recharge Operation to Reduce Nutrient Load in an Agricultural Basin: Delineation of Processes, Controls, and In-situ Potential
AU: * Schmidt, C M
EM: cschmidt@ucsc.edu
AF: Earth and Planetary Science, University of California, Santa Cruz, 1156 High St, Santa Cruz, CA 95064, United States
AU: Fisher, A
EM: afisher@ucsc.edu
AF: Earth and Planetary Science, University of California, Santa Cruz, 1156 High St, Santa Cruz, CA 95064, United States
AU: Wheat, G
EM: wheat@mbari.org
AF: University of Alaska Fairbanks, PO Box 475, Moss Landing, CA 95039, United States
AU: Sharkey, J
EM: jessica_sharkey@csumb.edu
AF: University of Alaska Fairbanks, PO Box 475, Moss Landing, CA 95039, United States
AU: Los Huertos, M
EM: Marc_LosHuertos@csumb.edu
AF: California State University, Monterey Bay, Earth Systems Sci. & Policy Dept., 100 Campus Center, Seaside, CA 93955, United States
AU: Lear, J
EM: lear@pvwma.dst.ca.us
AF: Pajaro Valley Water Management Agency, 36 Brennan Street, Watsonville, CA 95076, United States
AB: Nitrate is the most common nonpoint source pollutant in surface and ground water in the United States, and is a problem particularly in basins developed for agriculture. There is growing municipal and environmental demand for fresh water in basins that have been influenced by decades of agricultural activity. The goal of this research is to assess the potential for a managed aquifer recharge (MAR) system to improve water quality, with an emphasis on reducing the nitrate load to underlying aquifers. The Pajaro Valley Water Management Agency (PVWMA), in central coastal California, currently operates a MAR project that is permitted to divert and recharge up to 2.5 x 10⁶ m³/yr (2000 ac-ft/year) from a slough (wetland) to augment available ground water supplies. As a result of agricultural runoff and infiltration, diverted slough water is often rich in nitrate, as is the water in the underlying aquifer. However, nitrate concentrations in water samples recovered from the aquifer soon after MAR percolation are often relatively low, suggesting that nitrate may be removed as water percolates from the pond into the aquifer. Autonomous Osmosampler systems were deployed in the recharge pond and four nearby monitoring wells, as part of a pilot study, to collect fluid samples during and after pond operation. Samples collected with these instruments recorded the chemical arrival of water in the aquifer soon after percolation began, in some cases showing a 50% reduction in the concentration of nitrate. The chemical response in the aquifer recorded by the Osmosamplers was consistent with pressure data collected simultaneously in the monitoring wells, demonstrating that Osmosamplers should be useful tools for investigating changes in water quality associated with MAR operation. As this research project becomes fully developed during the 2007-08 water year, we will install Osmosampler systems in ground water monitoring wells surrounding the pond, and will collect shallow fluid samples using piezometers and lysimeters in the base of the pond, to asses chemical transformations that take place during MAR operation. We are particularly interested in quantifying the extent, rates and controls on denitrification, where and when nitrate loads are reduced, and under what physical and chemical conditions. Results of this study should have broad implications for the operation of MAR systems where available water has high nutrient concentrations.
DE: 0452 Instruments and techniques
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 1830 Groundwater/surface water interaction
DE: 1831 Groundwater quality
DE: 1880 Water management (6334)
SC: Hydrology [H]
MN: 2007 Fall Meeting