Martin A. Locke
National Sedimentation Laboratory, Agricultural Research Service, USDA

This paper summarizes some of the research at various scales by USDA-ARS National Sedimentation Laboratory scientists studying the effects of conservation management on water quality and ecology in agricultural watersheds in the Mississippi Delta Region, USA.

The Mississippi Delta Region is located in the central portion of the United States and occupies approximately 11 million hectares. The region comprises the southern portion of the Mississippi Alluvial Plain, extending from the state of Missouri to the Gulf of Mexico and is 1100 kilometers in length and widens to 160 kilometers in some places. The Mississippi Delta is intensively agricultural, with crop production predominantly comprised of soybeans, rice, corn, cotton, and catfish. Some aspects of agricultural management in this region have generated interest in evaluating environmental impacts.

The region has a humid temperate climate with an average annual rainfall of 114 to 152cm and average temperature of 18 C with periods of significant rainfall in the spring and winter months. The topography is relatively flat, averaging less than 1% slope, but significant quantities of sediment and chemicals are removed during intense rain events.

Traditional crop management in the Delta region involves several cultivations during a growing season. Tillage prior to heavy rainfall results in high sediment loss. Rapid growth of weeds during the growing season in this humid climate often requires the use of herbicides for effective control. Intense row cropping requires the use of fertilizer, especially nitrogen in non-legume crops such as corn and cotton. Fertilizers and herbicides are both considered potential contaminants of Mississippi Delta surface and subsurface water supplies.

Various approaches have been used to evaluate the impact of agriculture on the landscape and to assess ecological, water quality, and soil quality benefits derived from conservation practices. Studies range in scale from field plot to watershed studies. Research activities within study areas include analyses and evaluations of soil, edge-offield runoff (sediment, plant nutrients, pesticides), and water quality and ecology. Data collection in each research locale included information on farming practices, crops, farm chemical use, BMP’s, runoff, soil characterization, ground water, lake water, and fish.