Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 19, 2006
Publication Date: May 25, 2006
Citation: Cooper, C.M., Locke, M.A., Knight, S.S. 2006. Source Areas in the Lower Mississippi River Basin: Ills and Cures in the Yazoo River Basin. Abstract for the Lower Mississippi River Symposium, pp. 61-62. New Orleans, LA, June 1-2, 2006. Interpretive Summary: Abstract only. Interpretative summary not required.
Technical Abstract: The Mississippi River drains two thirds of the continental United States. This basin contains the largest amount of concentrated livestock and crop agriculture in the United States. Because of size and land use, the river transports enough nutrients produce plankton blooms. The dying plankton negatively impact oxygen concentrations, resulting in hypoxia in the Gulf of Mexico. Official work began on this problem in 1997 when EPA formed the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force. In 1998 Congress charged the multi-agency task force to conduct a scientific assessment of the causes and consequences of gulf hypoxia and provide a control strategy. Suggested solutions focused on reduction of inputs from source areas and creation of large areas of wetlands. Because of differences in land use, the need for better communication among affected neighboring states, and to develop an organized approach, the upper and lower basin states organized working groups. The Yazoo River basin only comprises 1.17 percent of the Mississippi basin area, but it was initially targeted as a major contributor of agricultural nutrients. Although further evaluation showed that the Yazoo basin produced 2.3 % or less of total N, 1% of nitrates, and 5.7 % or less of total P, there is general agreement that any nutrient reduction which can be achieved in a reasonable fashion will assist in providing a solution to the hypoxia problem. The Yazoo River basin is easily divided into two distinct source areas: the loess hills and the Mississippi alluvial plain. The hills and delta portions of the basin have almost equal portions of the 34,700 km2 basin. The hills have a mixture of forest, pasture, and row crops while the alluvial plain consists of ~80 % agriculture and 20 % bottomland hardwood forested wetland or other land use. A majority of the municipalities located in the basin have fewer than 10,000 residents. The major contribution from hill land source areas is sediment. The runoff that produces sediment also carries nutrients, but since the majority of hill land sediment comes from banks and beds of unstable streams, nutrient outputs are relatively low. Conversely, intensive cultivation of the fertile soils of the alluvial plain results in greater levels of N and P in runoff. While some delta soils are naturally rich in P, inputs from agriculture represent significant contributions of nutrients. In long-term evaluations of runoff from a typical hill land watershed, we found row crop watersheds contribute 0.5 mg/L and 0.09 mg/L of nitrate-N and total P, respectively, while forest areas contribute 0.02 mg/L nitrate-N and 0.01 mg/L total P. Conversely, similar watershed studies in the delta produced runoff concentrations for nitrate-N and total P of 1.7 mg/L and 0.8 mg/L, respectively. Research at the National Sedimentation Laboratory has shown that there are several on-farm best management practices that reduce nutrient losses. In-field actions include reduced tillage or no tillage, cover crops, filter strips, and stiffgrass hedges. Edge-of-field practices include farm ponds, detention basins associated with water stepdown structures (drop pipes) from farm fields to stream levels, seasonal adjustable slotted board drainage structures, constructed wetlands, vegetated ditches and natural habitats like forested bottomland hardwood wetlands.