Linda Benedict, Lutz, C. Greg, Romaire, Robert P., Mcclain, William R. | 11/30/2011 10:01:04 PM
Robert P. Romaire, W. Ray McClain and C. Greg Lutz
Water is an essential resource for aquaculture. No single factor influences the success of aquaculture operations more than the availability of good-quality water. Aquaculture is one of Louisiana’s major animal industries and, its $326 million contribution to the state’s economy makes it an important part of Louisiana’s agriculture. The Louisiana aquaculture industry includes more than 2,000 diverse operations throughout the state, including production of crawfish, catfish, alligators, oysters, tilapia, baitfish, soft-shell crawfish and crabs, ornamental fish, baby turtles and a variety of freshwater game fish and other minor species. Crawfish production typically accounts for slightly over half of the farm-gate value of Louisiana’s aquaculture crops.
In commercial aquaculture facilities, water use is directly related to effluent discharges. Greater water use results in greater water volumes being discharged, and this can potentially have a negative effect on receiving waters. Contributions of water to an aquaculture operation include precipitation, runoff, seepage inflow and the addition of surface water or groundwater through management, including filling ponds, flushing for oxygen management or replacing losses from evaporation and seepage. Water consumed in aquaculture includes water lost to evaporation, discharge and seepage; withdrawal of surface water or groundwater; and water removed in the biomass of harvested aquatic animals.
Water requirements for Louisiana aquaculture operations vary greatly depending on the type of culture system. Flow-through systems that require large volumes of water are not used commercially in Louisiana. Recirculating aquaculture systems, which are used on a limited scale for alligator, tilapia and bait-minnow farming in Louisiana, are minor consumers of water because the water is continuously recycled through mechanical and biological filters. Wa Lutz ter consumption is significant in crawfish and catfish farms that use outdoor earthen ponds, and these are dominant in Louisiana aquaculture. Water consumption in ponds varies widely depending on the frequency of water exchange and pond drawdowns (minor in catfish farming; significant in crawfish farming).
The amount of water consumed in crawfish and catfish farming is higher than for typical agricultural crops (Table 1), but aquacultural products generally have higher economic value per unit weight. Crawfish farming is Louisiana’s largest aquaculture industry with 184,000 acres in cultivation, so it will be used here to illustrate water consumption. About 11 percent of the water withdrawn from the Chicot aquifer system in southwest Louisiana is used for crawfish farming, compared with about 65 percent used for crop irrigation, principally rice. Water is required to fill crawfish ponds and replace losses from evaporation and levee seepage during the fall, winter and spring production season. Additional water is often used to flush ponds to maintain sufficient oxygen levels for crawfish.
AgCenter research has shown the total amount of water required to maintain a typical rice-field crawfish pond at near full-flood depth of 12 inches, from October flood-up through mid-June drawdown, is about 91 inches. About 40 percent of this water requirement will be supplied by precipitation, but the balance (60 percent) must be provided by surface water or groundwater. Of the 91 inches of water used, 68 inches will be consumed by evaporation and by transpiration by plants (Table 2). Effluent discharged during an average crawfish production cycle is 23 inches with end-of-season pond drawdown (37 percent), non-intentional discharge from precipitation overflow, excess pumping and levee breaks (29 percent), normal levee seepage (22 percent) and oxygen management (12 percent) accounting for the water releases (Figure 1).
The LSU AgCenter, with partners from government and industry organizations, has developed voluntary environmental best management practices (BMPs) for all of Louisiana’s aquaculture commodities. BMPs result in reduced water consumption and lower levels of nutrients, sediments, and organic matter being discharged into the state’s waters. These recommended practices are outlined in two new LSU AgCenter publications, Aquaculture Environmental Best Management Practices and Crawfish Environmental Best Management Practices (see back cover). These manuals provide guidance for the selec selection, implementation and management of practices that help growers conserve soil and protect water and air resources.
Often, aquaculture ponds can be managed to reuse water for other purposes. For example, tailwater (effluent) discharged in spring and summer from crawfish ponds can be used to irrigate and replenish water in rice fields, which are planted in mid-March through April.
Water use in aquaculture is essential, but wise use and management not only conserve the resource and protect the environment, they also reduce the cost of production and potentially increase profit margins.
Robert P. Romaire, Professor, Aquaculture Research Station; W. Ray McClain, Professor, Rice Research Station, Crowley, La.; C. Greg Lutz, Professor, Aquaculture Research Station, Baton Rouge, La.
(This article was published in the fall 2011 issue of Louisiana Agriculture magazine.)