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Climate change models suggest that many parts of the interior United States will become hotter and direr. One potential response to this is to increase the area of cultivated land under irrigation. Although increased irrigation may prove to be attractive to farmers, it is not without environmental costs--including potential damage to soils, water quality, and wildlife. The case of the Kesterson National Wildlife Refuge shows how failure to anticipate potential water-quality problems can lead to severe contamination and suggests that future public efforts to support irrigation should proceed with caution and a thorough understanding of risks.
The Kesterson National Wildlife Refuge was established in 1970 along the San Joaquin River in California's intensively farmed Central Valley (figure). The 5,900-acre (2,390-hectare)[1] refuge harbored a diverse array of migratory and resident waterfowl, including ducks, geese, herons, and coots, as well as an assortment of fish, mammals, and raptors. Located in a State that is estimated to have lost more than 90 percent of its wetlands over the past tow centuries, Kesterson appeared to be a crucial part of efforts to conserve California's biological heritage. In the spring of 1983, some of the ducks, coots, grebes, and stilts born at Kesterson Reservoir at the southeastern edge of the refuge emerged from their eggs deformed and crippled--with oddly shaped beaks, missing wings, twisted legs, and unformed skulls. Many died shortly after hatching. The U.S. Fish and Wildlife Service, which had investigated fish die-offs at Kesterson in 1982, conducted laboratory analysis that suggested that the disappearance of fish and the deformities of birds stemmed from a common cause--unusually high concentrations of selenium in the Kesterson Reservoir water. Trace amounts of selenium occur naturally in the soils of central California, as in many parts of the arid Southwest. The contamination of Kesterson Reservoir was caused by a combination of water development projects and irrigation practices. Selenium had leached from agricultural soils, moved through drainage systems, and became concentrated in the Kesterson Reservoir. At high concentrations, the selenium provided deadly. Kesterson Reservoir lies at the drainage end of the San Luis Unit of the Wetlands Water district, operated by the Bureau of Reclamation as part of the huge Central Valley Project. The saline soils of large sections of the San Luis area were not easily used for irrigated agriculture. The success of irrigated agriculture in saline soils depends on the application of enough water to flush salts out of the upper layers of soil. But the soils of San Luis presented an additional complication--they are underlain by an impenetrable layer of clay that prevents the drainage of irrigation water. If the soils were irrigated enough to flush away salts, the poor drainage would cause the water table to rise, drowning roods of crop plants and depositing more slats in surface soils. Subsurface drainage was necessary to make the cropland productive.
As part of larger efforts to bring water to the Central Valley, the Bureau of reclamation began planning water supply systems in the San Luis Unit starting in the 1950s, and by 1960 was authorized to begin construction of a system that came to include the San Luis Dam, Canal, and Reservoir. To achieve the proper balance of irrigation and drainage for agricultural production, the Bureau of Reclamation planned an extensive 188-mile (300-kilometer)[2] drainage system to take drainage flows from the San Luis Unit into the Sacramento-San Joaquin Delta. Only the first 85 miles of the drain were ever completed. By 1975, the drain had reached Kesterson Reservoir--and that is where it stopped. Controversy over potential effects on water quality in the Delta and lack of Federal funds prevented completion of the full drainage system.
Since 1975, drainage water carrying selenium and other salts leached from the San Luis soils have emptied into the Kesterson Reservoir. over the years, selenium and other potentially toxic trace elements concentrated in reservoir waters. The selenium was further concentrated in vegetation and small organisms on which waterfowl feed--a process known as bioconcentration--eventually producing the startling birth defects and mortality among young birds seen in 1983. Concern over possible risks to humans led the State to issue a health advisory, warning against eating duck hunted on the refuge. California's State Water Resources Control Board found concentrations of selenium up to 10 times higher than permitted by public health standards and other trace elements in amounts that exceeded Environmental protection Agency (EOA) water-quality standards. By 1985, the Board declared the San Luis drainage water a hazardous waste that would have to be treated and cleaned up accordingly. Drainage into the reservoir was finally halted in 1986. In less than a decade, Kesterson went from being a cornerstone of California's wildlife conservation program to a national symbol of environmental disaster. The Kesterson case is an extreme example of how irrigated agriculture may harm water quality--a particularly ill-fated confluence of Federal water projects, natural soil properties, and conflicting goals. However, the Kesterson problems are not unique. In the East, soluble salts have long ago been washed from the soils by rainfall. But in the West, the accessibility of salt-bearing formations and low rates of precipitation combine to make much of the region subject to salinity problems (figure below). Even on nonirrigated cropland, saline deposits can develop in areas of poor drainage. Dryland farming practices, alternating crop and fallow years (a possible adaptation to climate change), may themselves add to salinity problems. Crop-fallow rotations use less water than would natural vegetation, and the unused soil water can carry salts to low-lying areas.
Can a case like Kesterson happen again? Federal actions at water projects around the Nation will undoubtedly be more cautious in the future. However, in most Western States, irrigation and consumptive use still take priority, while protection of adequate water flows and water quality for wildlife, fish, recreation, and other natural uses receive short shrift (see ch. 5). Climate change may well increase the demand for water diversions for irrigation, potentially leading to increased conflicts over water use and environmental quality.
2 To convert miles to kilometers, multiply by 1.609.
SOURCES: Office of Technology Assessment, 1993; A. Dinar and D. Zibeman (eds.), the Economics and Management of Water and Drainage in Agriculture (Boston, MA: Kluwer Academic Publishers, 1991); R.W. Wahl, Markets for Federal Water: Subsidies, Property Rights, and the Bureau of Reclamation (Washington, DC: Resources for the Future, 1989).
