Climate Impacts On Water Quality in the Fort Cobb Reservoir (OK) Watershed.

Agriculture is a dominant land use in the U.S., and significant water quality concerns are associated with agricultural systems and practices.  It is essential to understand interactive effects of geology, geomorphology, soils, and climate, with agricultural systems so that we can improve environmental performance while sustaining productivity and profitability.  The Fort Cobb Reservoir, in southwestern Oklahoma, is listed by the Oklahoma Department of Environmental Quality as not meeting water quality standards, based on a high trophic level of the lake related to nutrients in the watershed.  A Total Maximum Daily Load plan was developed based on phosphorus (P) as the limiting nutrient, and agriculture as the primary source of P.  In 2001, the Oklahoma Conservation Commission established a 319 Water Quality Project in the watershed to promote adoption of conservation practices to reduce sediment and nutrient delivery to the reservoir.  The USDA Agricultural Research Service established research in the watershed as part of the Conservation Effects Assessment Project (CEAP).  Water quality samples were collected at 15 sites within the watershed at two week intervals from 2005-2008, and analyzed for suspended sediment, nitrogen, and phosphorus concentrations. The 4-year monitoring period included drought in 2005 and 2006, followed by wet conditions and extreme precipitation events in 2007 and 2008.  Spatial and temporal patterns of water quality parameters will be related to biophysical, ecological, and management factors in the contributing areas of each site.  Better understanding of the annual and interannual dynamics of climate and water quality parameters  will help in identifying conservation needs and developing strategies to mitigate water quality problems.