ABSTRACT
Selenium concentrations are elevated in subsurface drainwater in the Imperial Valley of California and in surface drains and rivers conveying irrigation drainage (Setmire et al., 1990, 1993). Selenium also is at levels of concern in biota utilizing these resources and in the Salton Sea. The Salton Sea area occupies a topographic and structural trough (Fig. 1). The trough is a landward extension of the depres sion filled by the Gulf of California, from which it is separated by the broad fan of the Colorado River Delta (Loeltz et al., 1975). The Salton Sea is a closed inland lake occupying about 930 km2 whose shoreline is currently at an elevation of about 78.3 m below sea level. At its southern end, the Salton Sea is the termi nus of the New and Alamo Rivers, which receive irrigation drainwater from a 2250 km drainage network in the Imperial Valley. The New River also receives municipal and industrial waste from the city of Mexicali, Mexico, along with agricultural return from the Mexicali Valley. The Salton Sea National Wildlife Refuge, located in the southern end of the Salton Sea, is a major waterfowl stopover on the Pacific Flyway. At its northern end, the Salton Sea receives agricultural return flow and runoff from the Coachella Valley via the Whitewa ter River.
