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<br />00Q770 <br /> <br />Water auality imoacts, Irrigation management that results in return flows has been targeted as an important <br />contributor to water quality problems in watershed basins with significant agricultural development. <br />Irrigation practices in the Grand Valley and on lands served by the lower Gunnison and its tributaries have <br />been identified as one factor contributing to increased salinity in the Colorado River (USDI, 1993), In <br />response to congressional action to comply with treaty obligations to Mexico, the Bureau of Reclamation has <br />developed and maintained programs to reduce this source of salt loading in recent years, <br />Nutrient and pesticide loading of surface and alluvial ground water can also arise from irrigation return <br />flows, Although potential nutrient loading from irrigated agriculture and confined animal feeding exceeds <br />that from urban sources in the South Platte basin, nutrient concentrations in surface water are highest <br />immediately downstream of the Denver-Metropolitan area (Litke, 1995). Because of nutrient uptake by <br />crops, irrigation diversions actually decrease nutrient loads in surface water to the extent that the levels of <br />nutrients leaving the basin are lower than total annual inputs from all sources, However, ground water <br />contamination from nutrients and pesticides is apparent in the areas of the South Platte basin where irrigated <br />agriculture is most concentrated (Austin, 1993), Although return flow from irrigation is one factor <br />contributing to contamination, the magnitude of this contribution in relation to other factors is unknown. <br /> <br />Imoacts of transfers to instream uses, Another issue involved in considering agricultural water conservation <br />is the fate of the resulting water, Irrigated agriculture is vital to the overall economy of Colorado, If water <br />resulting from conservation is transferred to municipal or industrial uses, this will tend to enhJll1ce the value <br />of this renewable resource to the state's economy, In addition, when agricultural water is transferred to the <br />alternative uses indicated above agriculture users are compensated for the loss, since the right to use water is <br />considered a property right. lnstream uses proposed for water resulting from agricultural water conservation <br />include recreation and improved habitat for threatened or endangered species, If the conserved water is to be <br />transferred to these uses, the same economic incentives for transfer must exist. In this case, the issue of who <br />pays becomes important. If the water is transferred for the purpose of enhancing the environment, the costs <br />and benefits of such changes in use have to be considered on an individual basis, <br /> <br />Irrigation Water Conservation - South Platte River Basin <br /> <br />Stratecies, Irrigators in the South Platte Basin rely on water storage and return flows to provide and <br />maintain water supplies, For example, farmers at the lower end of the system depend on river gains from <br />surface and ground water return flows to maintain river levels late in the season, The amount of reuse in the <br /> <br />47 <br />