Us Irrigation Return Flows Irrigation is the basis for life and crop production in arid croplands of America, particularly in the 17 western states. Not all of the water that is applied to crops, however, is taken up by the growing plants or held in the soil profile. Irrigation return or drainage water can pose environmental problems to surface or groundwater when it contains troublesome levels of dissolved salts, natural elements, nutrients or pesticides. An examination of California's challenges provides us an overview of this issue. Decades of surface irrigation has caused the leaching of selenium from soils in parts of the south and west sides of California's San Joaquin Valley and Imperial Valley.
Selenium is a naturally occurring trace element toxic to wildlife when concentrated.
Contributing to the problem are both surface runoff and subsurface drainage from systems used to drain excess or saline water from the root zone of dense, improperly drained soils. It will be difficult to achieve solutions that protects wildlife and the long-term productivity of the valuable farmland, yet doesn't adversely impact today's harvests. To solve the selenium problem other methods are being tried. Some states are purchasing the most problematic areas, taking them out of production and allowing native plant and animal populations to take over. In other areas, alternative wildlife habitat is provided to mitigate the effects of dangerous selenium levels in irrigation drainage collection basins.