The source, transport, and fate of selenium and other contaminants in hydrological and biological cycles of the Salton Sea area.
US Bureau of Reclamation, Salton Sea/Lower Colorado Study
The Salton Sea area is located in the southeast desert of California. It is bordered on three sides by mountains and adjoins the Mexicali Valley of Mexico on the south. The area occupies the northern part of the Salton Trough which is a topographic and structural depression. This depression is a landward extension of the Gulf of California, from which it is separated by the broad fan delta of the Colorado River.
Inflow to the Salton Sea comes from:
* The New River, a mixture of municipal, industrial, and agricultural flows from the City of Mexicali and agricultural drainage from the Imperial Valley;
* The Alamo River, predominantly agricultural drainage from the Imperial Valley;
* The Whitewater River, agricultural return flow from the Coachella Valley along with runoff from the local mountains;
* San Felipe Creek, flow from the local mountains.
There is no outlet to the Salton Sea.
Agriculture in the Imperial Valley occupies approximately 500 thousand acres and receives about three million acre-feet of Colorado River water from the All-American Canal for irrigation. The Salton Sea National Wildlife Refuge is at the southern end of the Salton Sea. Annually, over one million birds are estimated to migrate through the area, making the refuge a major stopover on the Pacific Flyway. The Salton Sea area provides significant wintering habitat for over 450,000 ducks, and up to 30,000 Snow and Ross's geese. At least 25 species of waterfowl have been identified in the area. Winter shorebird counts have documented over 55,000 birds, including 38 shorebird species which feed in the natural mud flats or refuge ponds.
Agricultural drainage from the Imperial Valley contains elevated levels of selenium and other salts as a result of evaporative concentration of irrigation water in the clayey soils. Birds feeding in the Salton Sea area are at risk of selenium contamination. This contamination occurs as lower food chain organisms accumulate selenium to higher levels than their surroundings and are fed upon by higher food chain organism. With each succeeding level, selenium concentration magnifies. At greatest risk are the larger fish-eating birds such as the double-crested cormorant, great blue heron, and the cattle egret which have fairly long food chains. Other birds such as the black-necked stilt, American coot, eared grebe, northern shoveler, and the ruddy duck also have elevated selenium concentrations in tissues, livers, and/or eggs. Concentrations, however, are lower because of shorter food chains..
As an outgrowth of the selenium contamination problem at Kesterson National Wildlife Refuge, in 1986 the Department of Interior's National Irrigation Water-Quality Program (NIWQP) selected the Salton Sea area for investigation. These studies, which have continued to the present, have documented the source, transport, and fate of selenium in the hydrologic and biologic cycles of the Salton Sea area. Other contaminants of concern include boron and organochlorine pesticide residues.
Current studies in the Salton Sea area are aimed at providing detailed information necessary for remediation to occur. Using information from previous investigations of water, bottom sediment, and biota in the Salton Sea area, these new studies have been designed to determine:
* The areal distribution of selenium in subsurface drainwater;
* Selenium concentrations in water and bottom sediments of surface drains conveying agricultural drainage;
* Biological uptake of selenium in surface drains;
* The biological use of surface drains and the Alamo River.
These current projects are multi-agency efforts involving the Bureau of Reclamation, U.S. Fish and Wildlife Service, U.S. Geological Survey, and Imperial Irrigation District.
Water related issues in the Salton Sea area are often complex, and, in many cases, present conflicting options where the solution to one problem exacerbates another problem. The Salton Sea Authority, comprised of the Coachella Valley Municipal Water District, County of Imperial, County of Riverside, and Imperial Irrigation District, was formed to address the problem of increasing salinity of the Sea. The Bureau of Reclamation is involved as a partner in these efforts as well as taking a leadership role in the on-going NIWQP activities. Imperial Irrigation District is actively involved in these activities as well as their own water-related programs. Oversight in all activities related to enforcement and interpretation of existing and future water-quality standards and criteria is provided by the Regional Water Quality Control Board, Region VII.