SOIL SELENIUM FRACTIONATION, DEPTH PROFILES AND TIME TRENDS IN A VEGETATED SITE AT KESTERSON RESERVOIR

Kesterson Reservoir, in the San Joaquin Valley of California, was used for disposal of saline, seleniferous agricultural drain waters during the years 1981 - 1986. The combined effects of infrequent drain water application, reduction and oxidation of Se, and evapotranspirative removal of soil water within the upper 1 m of the soil profiles appear to provide explanations for distribution patterns of Se in soils of upland sites. From 1987 to 1990, an approximate doubling in average soil solution Se concentrations was observed. It is shown that currently only relatively insignificant quantities of Se have been transported into the Pond 11 soils from the shallow water table. Sequential extraction of these upland soils indicated that substantial inventories of Se were associated with soluble, adsorbed, carbonate, and soil organic matter fractions, while Se retained within refractory inorganic fractions were minor. The mobilization of Se from these potentially labile pools may account for the observed increases in soil solution concentrations of Se following the draining of Kesterson Reservoir.