Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 20, 2009
Publication Date: September 7, 2009
Citation: Locke, M.A., Bingner, R.L. 2009. Assessments of Water Quality in Mississippi Delta Lake Watersheds. Water Quality Research to Evaluate the Effects of Agricultural Conservation Practices Utilized in the United States and India Workshop Proceedings. Allahabad Agricultural Institute–Deemed University, Allahabad, India. p. 11-12. Interpretive Summary: Abstract Only - Interpretative Summary not required.
Technical Abstract: This paper summarizes watershed scale research by USDA-ARS National Sedimentation Laboratory scientists on the effects of conservation management on water quality and ecology in oxbow lakes of 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 cotton, soybeans, rice, corn, 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 152 cm 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. Because of environmental concerns related to agricultural practices, representative farmers, grower organizations, and State and Federal Government scientists, representative farmers, grower organizations, and environmental groups in the Mississippi Delta region formed an alliance to conduct environmental research on working farm systems to help Delta growers implement best management practices (BMP’s) that address environmental concerns without reducing their overall profitability and productivity. In 1994, a research and demonstration project was organized by a consortium of State and Federal agencies and interest groups that became known as the Mississippi Delta Mississippi Evaluation Areas Project or MD-MSEA. The MD-MSEA was an expansion of a national effort coordinated by the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) in cooperation with other Federal and state cooperative agencies. The MD-MSEA project began with two primary objectives: (a) assess how agricultural activities affect water quality in the Delta; and (b) increase knowledge needed to design BMP’s as components of Delta farm systems. Focus of research activity centered on Delta oxbow lakes, remnants of rivers that have changed their course. Oxbow lakes are considered “closed systems” – all of the water in an oxbow lake watershed eventually drains to the lake. If BMP’s were installed, improvements could be measured in the water quality and fish communities in the lakes. Since oxbow lakes are common in the Delta, results found in the study areas would be applicable to other farms. The main emphasis of MD-MSEA consisted of three oxbow lake watersheds in the state of Mississippi. BMP’s were installed in the three watersheds incrementally. The largest watershed, Thighman Lake, was selected as a “control” where no BMP’s were installed. Beasley Lake watershed was chosen to have only edge-of-field BMP’s, such as slotted-board risers, slotted inlet pipes, filter strips, grassed waterways, and riparian forest management. These edge-of-field BMP’s were considered less costly, requiring no change in farming practices. Deep Hollow Lake watershed was selected to include edge-of-field BMP’s as well as farming practices, such as reduced tillage and cover crops. Research activities in the project were comprehensive by design, with much of the analyses and evaluations focusing on sediment, plant nutrients, pesticides, and lake ecology. Data collection in each watershed included information on farming practices, crops, farm chemical use, BMP’s, runoff, soil characterization, ground water, lake water, and fish. In 2003, the MD-MSEA project was phased out. However, one of the lakes, Beasley, was included in a new U.S. national research effort described as the Conservation Effects Assessment Project (CEAP). Beasley Lake Watershed (BLW) represents the U.S. Mississippi Delta Region in CEAP. The 915-ha (2260-ac) BLW drains into an oxbow lake that has been monitored since 1995 when row crops were grown on 79% of the area, and the remaining area included a 25-ha (62-ac) lake and a 135-ha (330-ac) riparian forest. Currently, row crops account for 66.5% of the area with 12.4% enrolled in the Conservation Reserve Program (CRP). Cotton (Gossypium hirsutum L.) acreage has decreased from 63.3% to 8.9%. Historical and current research in BLW focus on monitoring lake limnology, evaluating conservation practice effects on edge-of-field runoff, quantifying changes associated with the CRP, and modeling watershed responses. Applying combinations of conservation practices can significantly reduce non-point pollution. The utilization of the USDA Annualized Agricultural Non-Point Source model (AnnAGNPS) and the Riparian Ecosystem Management Model (REMM) together provides additional information on the effectiveness of conservation practices within the watershed by combining technology that assesses riparian buffer effectiveness in filtering nutrients at the field scale with the watershed water quality transport capabilities of AnnAGNPS.