Water Quality, Discharge Pollutants, Nitrogen And Phosphorus Budget In Five Types Of Aquaculture Pond

In order to reveal the discharge pollutants and sources of aquaculture pond, and providebasic data for aquaculture pollution reduction program, five types of aquaculture pond inSuzhou area were monitored on quality of source water, pond water, and discharge waterduring water exchanes as well as dry pond. The parameters included dissolved oxygen（DO）,pH, total nitrogen（TN）, total ammonia（TAN）, nitrite（NO₂-N）, nitrate（NO₃-N）, totalphosphorus（TP）, chemical oxygen demand(COD^Mn), total suspended solids（TSS）. Then theapparent pollutant intensity and true pollutant intensity of TN, TP, COD^Mnand TSS werecalculated. Finally, nitrogen and phosphorus budget of five types of aquaculture pond wereestablished based on the material balance principle. The main results were as follows:1. The water quality in five types of aquaculture pond: in polyfish-farming pond, TN2.36-3.50mg/L, TAN0.41-1.62mg/L, NO₂-N0.008-0.390mg/L, NO₃-N0.16-0.45mg/L, TP0.32-0.75mg/L, PO₄-P0.032-0.112mg/L, COD^Mn7.72-14.46mg/L, TSS20.20-70.44mg/L. Inoriental river prawn-farming pond, TN2.36-5.58mg/L, TAN0.19-1.88mg/L, NO₂-N0.003-0.066mg/L, NO₃-N0.02-0.41mg/L, TP0.33-1.64mg/L, PO₄-P0.013-0.358mg/L, COD^Mn10.72-26.59mg/L, TSS18.16-87.54mg/L. In whiteleg shrimp-farming pond, TN1.79-3.92mg/L, TAN0.34-1.40mg/L, NO₂-N0.008-0.497mg/L, NO₃-N0.13-0.36mg/L, TP0.23-0.87mg/L, PO₄-P0.015-0.197mg/L, COD^Mn6.78-14.61mg/L, TSS7.20-35.79mg/L. In giant riverprawn-farming pond, TN1.44-3.71mg/L, TAN0.37-1.11mg/L, NO₂-N0.005-0.468mg/L,NO₃-N0.09-0.40mg/L, TP0.21-0.80mg/L, PO₄-P0.025-0.168mg/L, COD^Mn5.04-13.37mg/L,TSS7.93-26.60mg/L. In crab-farming pond, TN0.71-1.43mg/L, TAN0.29-1.49mg/L, NO₂-N0.003-0.045mg/L, NO₃-N0.04-0.21mg/L, TP0.10-0.34mg/L, PO₄-P0.017-0.138mg/L, COD^Mn5.39-9.87mg/L, TSS6.52-21.00mg/L. The results showed that, water of the five types ofaquaculture pond was eutrophication status, DO and pH were at suitable scope, TAN wereover higher the suitable scope, NO₂-N most time were at suitable scope, in shrimp-farmingpond COD^Mnwere over higher suitable scope of shrimp farming.2. Concentration of TN, TP, COD^Mnand TSS in drainage of the five types of aquaculturepond were0.90-2.88mg/L,0.32-1.76mg/L,6.84-13.30mg/L,17.8-76.2mg/L, respectively. And at the same time in pond water were0.71-2.78mg/L,0.34-1.64mg/L,6.62-11.7mg/L,17.3-70.5mg/L, respectively. Pollutants concentrations in the clear pond drainage wereincreased except crab-farming pond. True pollutant intensity of TN, TP, COD^Mnand TSS inpolyfish-farming pond were16.82kg/hm²,4.73kg/hm²,112.4kg/hm²and259.9kg/hm²,respectively; in oriental river prawn-farming pond were45.6kg/hm²,13.1kg/hm²,266kg/hm²and779.7kg/hm², respectively; in whiteleg shrimp-farming pond were182kg/hm²,47.5kg/hm²,822kg/hm²and2278kg/hm², respectively; in giant river prawn-farming pond were144kg/hm²,41.3kg/hm²,629kg/hm²and2284kg/hm², respectively; in crab-farming pondwere16.82kg/hm²,4.73kg/hm²,112.4kg/hm²and259.9kg/hm², respectively. The truedischarge pollutants of TN, TP, COD^Mnand TSS in polyfish, whiteleg shrimp, and giant riveprawn culture ponds were12.25%-42.31%,21.12%-43.16%,12.24%-40.27%and49.18%-68.18%higher than the apparent discharge pollutants intensity. These resultsindicated that quality of pond water could be used to estimate discharge pollutants duringwater exchange rather than dry pond. True discharge pollutants of Whiteleg shrimp andpolyfish culture ponds were higher than other breeding ponds, and crab pond was the smallest,discharge pollutants would be reduced effectively by improved discharge technology.3. Condition of nitrogen and phosphorus of5types of aquaculture pond were as follows:The nitrogen budget equation of the polyfish-farming ponds was: fry43.68kg/hm²+feeds419.5kg/hm²+fertilizer5.23kg/hm²+water input117.7kg/hm²=catch165.1kg/hm²+effluence172.3kg/hm²+others248.7kg/hm²;the phosphorus budget equation was: fry10.39kg/hm²+feeds86.03kg/hm²+fertilizer3.45kg/hm²+water input14.79kg/hm²=catch34.29kg/hm²+effluence44.55kg/hm²+others35.82kg/hm². Nitrogen budget equation in freshwater shrimpponds was: juvenile shrimp6.76kg/hm²+feeds167kg/hm²+fertilizer33.8kg/hm²+water input46.9kg/hm²=catch32.1kg/hm²+effluence45.6kg/hm²+whterweed35.2kg/hm²+others141kg/hm²; phosphorus budget equation was: juvenile shrimp0.58kg/hm²+feeds34.7kg/hm²+fertilizer15.5kg/hm²+water input6.76kg/hm²=catch2.78kg/hm²+effluence13.1kg/hm²+waterweed4.40kg/hm²+others37.3kg/hm². Nitrogen budget equation was: juvenile shrimp0.09kg/hm²+feeds489kg/hm²+fertilizer3.04kg/hm²+water input50.0kg/hm²=catch155kg/hm²+effluence182kg/hm²+others206kg/hm²; phosphorus budget equation was: juvenileshrimp0.01kg/hm²+feeds112kg/hm²+fertilizer0.48kg/hm²+water input18.0kg/hm²=catch14.6kg/hm²+effluence47.5kg/hm²+others68.1kg/hm².Nitrogen budget equation in giantriver prawn was: juvenile shrimp0.26kg/hm²+feeds484kg/hm²+water input47.3kg/hm²=catch107kg/hm²+effluence144kg/hm²+others280kg/hm²; phosphorus budget equation was:juvenile0.004kg/hm²+feeds107kg/hm²+water input17.0kg/hm²=catch16.0kg/hm²+effluence 41.3kg/hm²+others66.5kg/hm².Nitrogen budget equation in carb ponds was: fry6.30kg/hm²+feeds135.5kg/hm²+water input29.11kg/hm²=catch30.08kg/hm²+effluence16.82kg/hm²+waterweed134.4kg/hm²+others-10.37kg/hm²; phosphorus budget equation was: fry0.51kg/hm²+feeds26.66kg/hm²+water input3.76kg/hm²=catch1.76kg/hm²+effulence4.73kg/hm²+waterweed16.80kg/hm²+others7.64kg/hm². Retention ratio of nitrogen and phosph-orus in feeds were15.20-31.60%and4.69-27.78%, respectively. The results showed that themain source of nitrogen and phosphorus in the five types of aquaculture pond was feeds, andthe retention ratio of nitrogen and phosphorus of feeds was low, improving the retention ratiowas an effective way to reduce pollution emissions in the pond.