Aquaculture contributes significantly to the world food supply, providing around 30% of fisheries production (Anonymous, 2001).
Because capture fisheries are being exploited to their sustainable limit and beyond, aquaculture is expected to continue to have an important role.
Aquaculture has become large enough to have significant impacts on the environment and natural resources, and a number of concerns have been expressed by both environmental activists and scientists (Dierberg and Kiattisimukul, 1996; Goldburg and Triplett, 1997; Naylor et al., 1998, 2000). The most serious concerns are the following:
- Destruction of mangrove, wetlands, and other sensitive aquatic habitat by aquaculture projects;
- Conversion of agricultural land to ponds;
- Water pollution resulting from pond effluents;
- Excessive use of drugs, antibiotics, and other chemicals for aquatic animal disease control;
- Inefficient utilization of fish meal and other natural resources for fish and shrimp production;
- Salinization of land and water by effluents, seepage, and sediment from brackish water ponds;
- Excessive use of ground water and other freshwater supplies for filling ponds;
- Spread of aquatic animal diseases from culture of organisms to native populations;
- Negative effects on biodiversity caused by escape of non-native species introduced for aquaculture, destruction of birds and other predators, and entrainment of aquatic organisms in pumps; and
- Conflicts with other resource users and disruption of nearby communities.
Of these and other possible negative impacts, water pollution by pond effluents is probably the most common complaint, and this concern has attracted the greatest official attention in most nations (Tookwinas, 1996; Boyd and Gautier, 2000; Boyd and Tucker, 2000).
Most shrimp and fish production is conducted in ponds, and ponds have effluents after heavy rains and when they are drained (Boyd and Queiroz, 2001). Water also is discharged from some ponds in response to water exchange. Although there is considerable interest in water reuse, or closed-cycle production systems, it currently is not technically or economically feasible to conduct most types of aquaculture without discharge.
Fertilizers and feeds are applied to ponds to promote shrimp and fish production, and normally, no more than 25% to 30% of the nitrogen and phosphorus applied to ponds in fertilizers and feeds is recovered in fish or shrimp at harvest (Boyd and Tucker, 1998).
Ponds have a remarkable ability to assimilate nitrogen and phosphorus through physical, chemical, and biological processes (Schwartz and Boyd, 1994a). Nevertheless, ponds often have higher concentrations of nutrients, plankton, suspended solids, and oxygen demand than the water bodies into which they discharge (Schwartz and Boyd, 1994b).
Thus, pond effluents are potential sources of pollution in receiving waters. Because of coercion by environmental advocacy groups, many nations are beginning to make regulations for aquacultural effluents.
Some European nations have made relatively strict regulations for cage and net pen fish culture. Australia has developed regulations for pond culture of fish and shrimp.
The National Pollution Discharge Elimination System (NPDES) of the United States Clean Water Act has allowed individual states to apply NPDES permits to aquaculture effluents for many years.
Most states with significant aquacultural production, however, have not required NPDES permits for aquaculture because the United States Environmental Protection Agency (USEPA) has made no federal rule for aquaculture effluents.
The USEPA has initiated a rule-making procedure for aquaculture, and the final rule will be available on 30 June 2004 (Federal Register, 2000). After this, aquaculture projects in all states will be subject to regulation by the federal rule.
Many tropical nations also have made aquaculture effluent regulations. Some examples are Belize, Brazil, Ecuador, India, Mexico, Oman, Thailand, and Venezuela. Aquaculture associations are concerned about the possible effects of environmental criticisms on the markets for their products.
There is a growing trend of environmental awareness by aquaculture associations, and they are promoting environmentally responsible production methods. There also is widespread interest in the economic advantages of products certified to be ‘‘environmentally friendly.’’
Effluent regulations mandated by governments often require compliance with water quality standards containing numerical criteria (Gallagher and Miller, 1996; Mackenthun, 1998). Alternatively, regulations sometimes are based mainly on mandated use of environmentally responsible practices (Gallagher and Miller, 1996; United States Environmental Protection Agency, 1995).
Even when regulations are based solely on effluent standards, aquaculture producers will find it necessary to improve production methods in order to comply with water quality criteria in permits.
The purpose of this report is to discuss actions that have been initiated to improve the management of aquaculture farms for the purpose of preventing or lessening the pollution of natural waters by pond effluents. The focus is on international efforts, but examples from the United States also will be given.
Author:
Claude E. Boyd
