232 posadas

Constructed Wetlands in Pond Effluent Reduction: 

Constructed Wetlands in Pond Effluent Reduction Benedict C. Posadas Assistant Economics Extension/Research Professor

Participating Agencies: 

Participating Agencies MSU-Coastal Research and Extension Center, Biloxi, MS David Veal, Head Mark LaSalle, Estuarine Ecologist MSU-Coastal Aquaculture Unit, Gulfport, MS Mississippi Power Company, Gulfport, MS Delta Pride Catfish, Inc., Indianola, MS

Funding Agencies: 

Funding Agencies U.S. Department of Agriculture NRI -1992-94 NRI- 1995-98 U.S. Department of Commerce SK - 1995-98

Objectives: 

Objectives evaluate effectiveness of constructed marsh systems toward improving water quality in aquaculture ponds determine optimal design and operating criteria for constructed wetlands determine the concomitant reductions in risk of crop loss, incidence of off-flavor, and release of nutrient-laden effluent into the environment

Objectives: 

Objectives determine the improvement in fish growth and feed conversion, and document the costs versus benefits of using this technology in pond culture

Methods: 

Methods Pond Size: 1/4-acre ponds 125 ft. long 85 ft. wide 4 ft. deep

Fish Species: 

Fish Species Channel catfish (Ictalurus punctatus) Phase II fingerlings (6-7 inch)

Wetland Plants: 

Wetland Plants Duck Potato (Sagittaria lancifolia) planted at 1/2- ft. centers

Experimental Design: 

Experimental Design Control ponds (no marsh, simulated water flow) Treatment ponds (marshes of “standard” size and flow rate).

Wetland Size Variations: 

Wetland Size Variations % of pond surface area small, 15% standard, 25% large, 35%

Flow rate Variations: 

Flow rate Variations Slow 3.25gal/min 3-day retention Standard 6.5 gal/min 2-day retention Fast 13.0 gal/min 1-day retention Very fast 26.0 gal/min 1/2-day retention

Monitoring: 

Monitoring Water Quality in Wetlands (inlet and outlet) Weekly: salinity, pH, ammonia, nitrite, nitrate, total phosphorous, total suspended solids

Water Quality in Ponds: 

Water Quality in Ponds Daily (twice per day): dissolved oxygen temperature Weekly: same as for wetlands chlorophyll a phaeophytin

Statistical Analysis: 

Statistical Analysis Analysis of Variance using General Linear Model (GLM) Means compared using SNK multiple range test All tests conducted at significance level of 0.05

Constructed WetlandsMSU-CAU, 1997: 

Constructed Wetlands MSU-CAU, 1997

Percent changes of inlet to outlet values of weekly water quality variables in wetlands of variable sizes, 1997: 

Percent changes of inlet to outlet values of weekly water quality variables in wetlands of variable sizes, 1997

Pond AerationMSU-CAU, 1997: 

Pond Aeration MSU-CAU, 1997

Mean values of daily pond water quality variables in ponds with wetlands of variable sizes, 1997: 

Mean values of daily pond water quality variables in ponds with wetlands of variable sizes, 1997

Mean values of weekly water quality variables in ponds with wetlands of variable sizes, 1997: 

Mean values of weekly water quality variables in ponds with wetlands of variable sizes, 1997

Mean values of weekly water quality variables in ponds with wetlands of variable sizes, 1997: 

Mean values of weekly water quality variables in ponds with wetlands of variable sizes, 1997

Dried Matter from Water SamplesMSU-CAU, 1997: 

Dried Matter from Water Samples MSU-CAU, 1997 14P - Sample from Pond 14 14I - Sample from Inlet 14O - Sample from Outlet

Catfish Stocking DensitiesPer Production Acre: 

Catfish Stocking Densities Per Production Acre 5,000 3-4 inch in 1994 6,000 7-8 inch in 1996 8,000 7-8 inch in 1997

Catfish Survival Rate: 

Catfish Survival Rate

Catfish YieldPounds Per Qtr Acre: 

Catfish Yield Pounds Per Qtr Acre

Catfish Off-flavor Scale: 

Catfish Off-flavor Scale

Wetland Electricity UseKWH Per Week: 

Wetland Electricity Use KWH Per Week

Chemical Costs $ Per Qtr Acre: 

Chemical Costs $ Per Qtr Acre

Net Feed Conversionlbs of feed per lb of fish gained: 

Net Feed Conversion lbs of feed per lb of fish gained

Daily Aeration Hours: 

Daily Aeration Hours

Catfish Pond-Wetland Systems: 

Catfish Pond-Wetland Systems Six 8-water-acre catfish ponds (CCF) Six constructed wetlands built adjacent to catfish ponds: 15% of pond size or 1.2 acres each 25% of pond size or 2.0 acres each 35% of pond size or 2.8 acres each

Catfish Stocking and Production, 1997: 

Catfish Stocking and Production, 1997 Stocking rate: 8,000 fingerlings per acre Stocking size: 7-8 inch CCF fingerlings Culture period: 8 months Survival rate: 57 percent Catfish yield: 6,744 pounds per acre Net feed conversion ratio: 1.0:2.4 Catfish off-flavor scale: greater than zero

Total Investment Requirements: 

Total Investment Requirements

Average Investment RequirementsPer Production Hectare: 

Average Investment Requirements Per Production Hectare

Added costs of constructed wetlands in recirculating catfish pond production$ per production hectare : 

Added costs of constructed wetlands in recirculating catfish pond production $ per production hectare

Added costs of constructed wetlands in recirculating catfish pond production$ per kilogram of catfish yield: 

Added costs of constructed wetlands in recirculating catfish pond production $ per kilogram of catfish yield

Conclusions: 

Conclusions Wetlands do appear to significantly reduce the levels of nutrients from catfish pond effluents Wetlands that are sized to about 25% of pond area with a 2-day retention time appear to provide optimal treatment of effluents No significant differences in the yield of marketable catfish. Higher investment requirements and operating costs.

Recommendations: 

Recommendations Testing in commercial farms. Use of other economically important culture species. Testing other plant species and methods of creating vegetation.

Constructed Wetlands Website: 

Constructed Wetlands Website http://www.msstate.edu/dept/crec/cwres.html http://www.msstate.edu/dept/crec/crec.html Go to Aquaculture msucares.com Go to Centers and Institutes Go to Coastal Research and Extension Center Go to Aquaculture