Stream Salinization by Inland Brackish-Water Aquaculture

Abstract

Commercial aquaculture is performed in several regions of Alabama, with much of the production being concentrated in the Blackland Prairie region. Portions of this region have access to aquifers containing brackish water with salinities ranging from 1 to 10 g/L that are currently supplying water to several pond-based aquaculture facilities. The use of low-salinity water has been beneficial for the production of channel catfish Ictalurus punctatus, and such water has been found suitable for the culture of marine species such as the Pacific white shrimp Litopeneaus vannamei. Though the use of this resource has been recognized as beneficial, the potential for it to salinize local surface waters is unknown. An element of concern associated with the salinization of streams is the chloride ion. The U.S. Environmental Protection Agency has established an instream standard chloride concentration of 230 mg/L for freshwater, which has been adopted by the Alabama Department of Environmental Management. Investigation into stream salinization resulting from low-salinity aquaculture in western Alabama was initiated in June 2006. Eight streams were sampled bimonthly for salinity, conductivity, and chloride concentration. Four of the eight streams are associated with aquaculture production facilities and receive effluents from these operations. The remaining four streams are located near the aquaculture facilities but do not receive effluents or runoff from them. The facilities include a catfish fingerling facility, a catfish production facility, a shrimp production facility, and a combined catfish–shrimp production facility. The streams associated with the aquaculture production facilities were sampled at sites both upstream and downstream from them. Sampling through April 2007 revealed that the streams associated with the aquaculture facilities had chloride concentrations exceeding 230 mg/L at various times during the year. These results indicate that these facilities are contributing to stream salinization.

Received January 29, 2010; accepted August 18, 2010