Lewis Gaston, Bollich, Patrick K.
Because the land is so flat, water flow in Bayou Plaquemine Brule and its tributaries, including Cole Gully, is sluggish and reaeration potential is low. Consequently, inputs of oxygen-depleting materials, such as dissolved or suspended organic material or ammonical nitrogen, are expected to aggravate this naturally oxygen-poor condition. Agriculture is the predominant land use, and rice, soybean, grain sorghum and crawfish are the principal crops in the Cole Gully watershed. Surface runoff, flood release and storm overflow from these production systems are the major sources of flow in Cole Gully, and agricultural production is the likely origin of water quality problems.
In 2003, LSU AgCenter scientists initiated a project that monitors differences in the quality of water released from a pair of fields used for rice, soybean and grain sorghum production. One field is under best management practices (BMPs), and the other is not. Water quality is being monitored both in edge-of-field comparisons and in Cole Gully itself.
The objectives of this demon-stration project are to measure the effectiveness of in-field conservation practices, quantify their benefits on water quality at the production-field scale and provide watershed-scale data on improved water quality in Cole Gully following widespread adoption of BMPs. Results from the study will also assist efforts by the Louisiana Department of Environmental Quality (LDEQ) and the U.S. Department of Agriculture Agricultural Research Service in validating what is termed the Annualized Agricultural Nonpoint Source water quality model for low-relief landscapes and rice production systems.
The approximately 6,000-acre Cole Gully watershed is a mosaic of leveed fields separated by a network of drainage ditches that feed into Cole Gully. The extensive human-made drainage system is ideal for this project because individual production fields are hydrologically isolated from one another. Because the volume and com-position of both runoff and discharge water are needed to determine edge-of-field sediment and nutrient losses, the first task was to locate adjacent rice row crop fields small enough to each be drained by a single pipe.
The U.S. Environmental Protection Agency (EPA) provides funds under the Clean Water Act to implement approved nonpoint-source management programs. These programs include a variety of components, including tech-nical assistance, education, training, technology transfer, demonstration projects and regulatory programs.
Agricultural producers in the Cole Gully area have been extremely supportive of the project. A majority of the production acreage in the watershed and essentially all acreage upstream of the water-quality samplers in the Cole Gully channel are now in some form of BMP manage-ment. Edge-of-field water quality data are expected to demonstrate the potential of BMPs, and stream samples are expected to show that the prescribed reduction in oxygen-depleting materials is being met. Early data on both points are encouraging.