COASTAL RESEARCH AND EXTENSION CENTER
Use of constructed wetlands in finfish pond culture water recirculation was studied to evaluate their effectiveness in improving water quality, determine optimal design and operating criteria and assess the associated benefits and costs in finfish pond production. Sixteen quarter-water acre ponds and 13 constructed wetlands of varying sizes and retention times were used in the experiment. Of the 13 wetlands used in the experiment, eight were two-year-old marsh systems originally planted with Juncus effusus and Sagittaria lancifolia at equal densities. Subsequently, Juncus effusus showed poor survival in all but one wetland and its use was discontinued. These plants were initially planted on 1-ft centers in September 1993. Additional Sagittaria lancifolia were planted in these wetlands in November 1995 to replace those plants which did not survive and increase vegetative coverage (1/2-ft centers). Phase II Ictalurus punctatus fingerlings were stocked at a rate of 2,000 fingerlings/pond.
Except for salinity and pH, wetlands were shown to significantly reduce levels of most parameters at the following rates: total ammonia (2-63%), nitrite (29-97%), nitrate (28-80%), total phosphorus (52-95%), total suspended solids (2-76%) and pH (0.5-10%). In general, wetlands of standard size and flow rate showed the highest levels of reduction for most parameters. Vegetative characteristics of wetlands also indicate that wetlands of standard size and flow rate were optimal in assimilating available nutrients. Results of pond monitoring showed that ponds with wetlands had dampened daily fluctuations in dissolved oxygen and reduced levels of photosynthetic pigments compared to control ponds. These ponds also required less aeration than control ponds. Levels of nutrients within ponds with wetlands were highly variable among treatments and were not less than those in control ponds, but were within tolerable ranges for fish production.
The added benefits and costs associated with the use of constructed wetlands in intensive and recirculating catfish pond production were estimated by applying the experimental results to a multi-enterprise commercial farm in the Mississippi Black Belt area. The initial investment requirements for six 8-water-surface acre catfish ponds on a multi-enterprise farm in the Mississippi Black Belt area were $3,527/acre. With six 1.2, 2.0 and 2.8-water-surface-acre wetlands built adjacently to the catfish ponds, total initial investment requirements rose by $2,656, $4,160 and $5,665/acre, respectively. Total specified operating and ownership costs of the 48-acre Mississippi Black Belt catfish enterprise without constructed wetlands amounted to $184,074/year, averaging $3,835/acre or $0.57/lb. When six 1.2, 2.0 and 2.8-acre constructed wetlands were added to the catfish enterprise, total costs rose by $0.052, $0.059 and $0.079/lb, respectively. In the short-run, the use of six 1.2, 2.0 and 2.8-acre constructed wetlands in a 48-water-acre catfish farm in a multi-enterprise Mississippi Black Belt farm area would be acceptable to farmers if the annual yield of marketable catfish would increase by 7, 5 and 7%, respectively.
A copy of the FINAL REPORT can be downloaded in portable document format.