ABSTRACT

In the western United States, saline drainage waters from irrigated fields are often disposed of by transferring them to sinks for storage, leaching, and evaporation. The evaporative concentration of trace elements has led to elevated concentrations of selenium (Se) in soils and waters of the Kesterson Reservoir located on the west side of the San Joaquin Valley, California [1]. Deaths and deformities of wildfowl linked to elevated Se levels [2] led to an upsurge in research activity, much of which is summarized in this volume. Recently, attention has focused on other irrigation/ drainage projects in California, Utah, Nevada, Wyoming, and other states where evidence is emerging that concentrations of Se (and perhaps other trace elements) in soils, surface waters, and aquatic biota are sufficiently high to be of concern [3,4]. Drainage water is most often discharged into aquatic environments (i.e., evaporation ponds, wetlands, streams), but the apparent sensitivity of these ecosystems to Se is causing fundamental changes in water management strategies. Examples are the closure of the San Luis Drain, which released agricultural drainage water into Kesterson, and the cessation of drainage water deliveries into other evaporation ponds in the valley, with the

highly salinized sediments contained therein reverting to terrestrial ecosystems (i.e., soils).