AGRICULTURE AND WILDLIFE - ECOLOGICAL IMPLICATIONS OF SUBSURFACE IRRIGATION DRAINAGE

Subsurface agricultural irrigation drainage is a wastewater with the p otential to severely impact wetlands and wildlife populations. Widespr ead poisoning of migratory birds by drainwater contaminants has occurr ed in the western United States and waterfowl populations are threaten ed in the Pacific and Central flyways. Irrigated agriculture could pro duce subsurface drainage and wildlife problems in other countries beca use several. of the factors contributing to toxic drainwater in the we stern U.S.A. (e.g. marine sedimentary basins with soils containing ele vated concentrations of trace elements such as selenium and molybdenum ; alkaline conditions that favor the formation of water-soluble forms of trace elements; soil salinization problems that require the use of irrigation to hush away excess salts), also occur in other arid region s of the world. Proposed agricultural irrigation projects should under go a technical review to assess water demand and supply relationships, and to determine the potential for drainage problems. Environmental a ssessments should be made at existing irrigation projects to determine if subsurface drainage is present or could occur in the future. Antic ipating and evaluating potential problems will allow changes to be mad e in irrigation practices for the benefit of agriculture and wildlife. The agricultural demands on water have reduced freshwater flows and a ffected the quantity and quality of wetlands throughout the world for decades. Subsurface irrigation drainage is yet another threat to the p recarious existence of many wildlife populations.