Improving Water Quality in Crawfish Aquaculture

Linda Benedict  |  4/5/2005 1:15:03 AM

Both rain and the flushing of crawfish ponds produce effluent.

Robert P. Romaire, Landon D. Parr and W. Ray McClain

Aquaculture operations worldwide have come under scrutiny because of potential environmental degradation caused by the discharge of water from production facilities. The U.S. Environmental Protection Agency (EPA) is reviewing aquaculture as an industry for regulatory activity. Most of Louisiana’s 129,000 acres of crawfish ponds are located in southwestern and south central Louisiana in water basins identified by the Louisiana Department of Environmental Quality (LDEQ) as impaired. Nearly half the acreage is in the Mermentau and Vermilion-Teche river basins.

Many farmers cultivate crawfish in rotation with field crops such as rice and soybeans. They have to flush the ponds intermittently in fall and spring to maintain oxygen at acceptable concen-trations for crawfish. This results in effluent discharge. Effluent also is released from crawfish ponds into streams and rivers during rainfall events. Ponds are drained annually in late spring or early summer to induce crawfish to burrow for reproduction and to establish a forage crop. The quantity and quality of effluent from crawfish farming operations and the impact on stream water quality in these impaired water basins is not known.

LSU AgCenter researchers are assessing how effluent from commercial crawfish farms contributes to water quality in southern Louisiana streams, with focus on the Mermentau and Vermilion-Teche river basins. Best management practices (BMPs) aimed to improve stream water quality and conserve natural resources, especially water, are being evaluated. Although pond management affects the characteristics and quantity of substances discharged from crawfish ponds, few data are available on water management practices used by the state’s crawfish farmers. Water management practices, and subsequent effects of effluents, may differ depending on factors such as type of culture system (single-crop crawfish, double-crop rice/crawfish or double-crop rice/crawfish rotation), source of water (surface or groundwater), size of farming operation, forage (rice or volunteer vegetation) and crawfish harvesting decisions.

The acreage and geographical locations of crawfish ponds in southern Louisiana parishes are being determined using geographical information systems (GIS) technology and Natural Resources Conservation Service (NRCS) data-bases. After validation of the data, crawfish production areas will be described by water basin and watershed. A survey is being conducted to identify crawfish farmers’ existing water and pond management practices to estimate the frequency and magnitude of effluent releases, as well as the potential for adoption of crawfish aquaculture BMPs.

Three commercial farming oper-ations in the Bayou Plaquemine-Brule Cole Gully watershed in Acadia Parish, which are being used in the rice-soybean BMP project, are also being used as study sites for the crawfish BMP project. As with the rice-soybean project, the quality and quantity of water released from paired crawfish ponds under BMP and non-BMP management are being monitored. BMPs include increasing pond water storage capacity to capture rainwater, thereby reducing effluent release during precipitation events, and altering late-season harvesting practices and end-of-season pond draw-down procedures to reduce sediment and nutrient loads in the effluents. These data will be used with information from the rice-soybean BMP project and other data to calibrate and validate LDEQ’s water quality computer model for different levels of conservation BMPs implemented in the Bayou Plaquemine-Brule watershed.

Best management practices have been determined to be an effective and practical means for reducing point and nonpoint water pollutants to levels compatible with environmental quality goals. In addition to providing a highly valued and desirable seafood product, crawfish ponds serve as favorable wetland habitat to many species of waterfowl, wading birds and furbearers. Often land that is marginal for traditional row crops is used in crawfish production. Integration of crawfish aquaculture with traditional agricultural land uses serves as a practical means of land and water conservation.

Robert P. Romaire, Professor and Resident Director; Landon Parr, Research Associate, Aquaculture Research Station, Baton Rouge, La.; and W. Ray McClain, Professor, Rice Research Station, Crowley, La.

(This article appeared in the spring 2004 issue of Louisiana Agriculture.)

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