SOURCES AND IMPACTS OF IRRIGATION DRAINWATER CONTAMINANTS IN ARID WETLANDS

Arid wetlands are being contaminated by subsurface agricultural irriga tion drainage throughout the western United States. Historic freshwate r inflows have been diverted for agricultural and municipal use, and r emaining freshwater supplies are not sufficient to maintain the integr ity of these important natural areas once they are degraded by irrigat ion drainwater. Waterfowl populations are threatened in the Pacific an d Central Flyways; migratory birds have been poisoned by drainwater co ntaminants on at least six national wildlife refuges. Subsurface irrig ation drainage is the most widespread and biologically important sourc e of contaminants to wetlands in arid regions of the country. The case history of poisoning at Kesterson National Wildlife Refuge in Califor nia and studies at other locations by the U.S. Department of the Inter ior provide detailed information on the toxicity of drainwater contami nants to fish and wildlife. Biogeochemical conditions favorable for th e production of toxic drainage are found throughout the western states . Two actions seem necessary to prevent further drainage-related degra dation of arid wetlands. First is a reduction in the amount of contami nants reaching these wetlands, possibly involving regulatory intervent ion through the National Pollutant Discharge Elimination System permit process. Second, a better balance must be achieved in the way fresh w ater is allocated between agriculture and wildlife. Federally subsidiz ed water has supported agriculture at the expense of wetlands for near ly 100 years in the western United States. This trend must be reversed if arid wetlands and their fish and wildlife populations are to survi ve.