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United States Department of Agriculture

Agricultural Research Service

Title: Changes of Soil and Plant Tissue Selenium Status in An Upland Grassland Contaminated by Selenium-Rich Agricultural Drainage Sediment after Ten Years Transformed from a Wetland Habitat.

item Banuelos, Gary

Submitted to: Ecotoxicology and Environmental Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2000
Publication Date: N/A

Interpretive Summary: Pyrite-containing rocks of marine origin occur along the western margin of the San Joaquin Valley in central California and contain significant amounts of Se. Natural weathering of these Se-containing rocks and minerals in conjunction with irrigation practices, redistributed Se and salts to shallow aquifers, streams, and/or wetland areas. In the central Valley of California, the saline inflow was discharged and stored in evaporation ponds at the Kesterson National Wildlife Refuge. As a result, Se toxicities were first observed in waterfowl frequenting the Refuge. Subsequently, Kesterson Reservoir was closed to additional drainage water. The Water Resource Control Board initiated a partial filling of the ponds at the Reservoir with uncontaminated soil. Hence a new management study was proposed, involving a natural management to dissipated Se by biological volatilization. If the emethylation of Se could be maintained at 5% losses per year, half of the S inventory in the upper 60 cm would be removed in 14 years. Ten years after filling the ponds with fresh soil, soil and plant samples were again collected and analyzed for Se concentrations. Results show that the potential for food chain contamination with Se has been naturally reduced at Kesterson Reservoir.

Technical Abstract: A field survey was conducted in 1989, 1994, and 1999 on soil and vegetation Se concentrations at the Kesterson upland grassland contaminated by Se-rich drainage sediment. The rate of Se dissipation via volatilization is estimated to be as high as 5% in the soil Se concentrations between 0 and 60 cm. Increased Se levels between 0-15 cm indicate that the natural vegetation is taking up Se from the lower soil profile and deposited it near the soil surface. This uptake process may reduce the rate of leaching of soluble Se. The average plant tissue Se concentrations and soil water extractable Se detected in 1999 was 10 ug Se/g and 110 ug Se/kg, respectively. The previous wetland had water Se concentrations over 300 ug, Se/L and aquatic plants with concentrations over 60 ug Se/g. Soil concentrations were at least 10% higher between 0-60 cm in a994. The data indicate that vegetation contributed to the measured reductions of the total Se inventory. Further reductions are likely dependent on soil redox chemistry that is influenced by the plant's roots. Future monitoring should place greater emphasis on the role of plants on soil Se reoxidation and the processes of soil Se dissipation.

Last Modified: 4/17/2015
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