Study On Potential Eutrophication And Bioremediation System In Fish-cage Culture Of Xiangshan Harbor

Fish cage culture is one of the important ways of aquaculture, the rapid development ofmarine aquaculture has made great contributions to the development of aquaculture in China.However, pollution phenomenon of cage culture itself limits on the sustainable developmentof aquaculture, and at the same time, caused a lot of nutrition load. Therefore, the method tocontrol nitrogen, phosphorus emissions, reduce the eutrophication and restore the health ofMarine aquaculture ecological system has become an important problem need to be resolved.In this paper, The eutrophication in fish cage areas has been investigated and evaluated, andseaweed was applied to set up a integrated multi-trophic aquaculture system. The ecologicalrestoration effects were evaluated in bioremediation stage. First of all, the investigation andnutritional assessment of seawater and sediment was carried out, and including thedistribution of phytoplankton. Then, the system of bioremediation by seaweed waspreliminary established, and the effects of the restoration were evaluated. Finally, nitrogenand phosphorus nutrition cycle routes in fish/algae integrated cage culture system werestudied. The ratio model of fish and algae would provide important theory data for developingof fish/algae integrated cage culture system. The main research results are as follows:1. Effect of fish-cage culture on environment in Xiangshan HarborOn the basis of investigation data, the eutrophication in fish cage areas was very serious inXiangshan Harbor. The range concentration of inorganic nitrogen was0.726-1.133mg/L, theconcentration of NO3-N accounted for74.83%of DIN and was the main form of inorganicnitrogen in the fish-cage culture areas. The range concentration of inorganic phosphorus andsilicate were0.043~0.082mg/L and0.794~1.357mg/L, respectively. The concentration ofinorganic nitrogen and inorganic phosphorus were too high to satisfy the Grade II of “Seawater Quality Standard”(GB3097—1997). The ratio of N to P was34.02, so N was relativesurplus. According to the value of eutrophication index (E) and organic pollution index (A),the seawater was eutrophication state, and the organic pollution was quite serious.The concentration of TN and TP in the sediment was serious excessive. The rangeconcentration of TN and TP was653.1~2457.1mg. Kg-1and310.6~819.4mg.Kg-1,respectively. The distribution of TN and TP was in center cages were higher than both in theborder regions and off lying aeras, and range of pollution was more than100m, thedispersion of sediment was severely. Pollution source of total nitrogen and phosphorus and organic carbon pollution may homologous, culture activities has an important contribution onseawater and sediment eutrophication. The results revealed that the water quality wasseriously polluted, so the red tide disaster might occur when the hydrometeorologicalconditions is suitable.2. Bioremediation of cage fish culture by Gracilaria chouae in an integrated multi-trophicaquaculture systemGracilaria chouae in an integrated multi-trophic aquaculture system was investigated, thedata monitored in the bioremediation stage showed that Gracilaria were obviously good onbioremediation effect. The maximum removing efficiency of NO3-N, NO2-N, NH4-N andPO4-P in bioremediation area I and II were37.76%and25.48%，36.99%and22.02%，29.27%and18.50%，40.64%and27.11%. the benefits of bioremediation area I by G. chouae wasbetter than bioremediation area II. In the meantime, the turbidity and the concentration ofchlorophyll a were decreased, and the dissolved oxygen was increased. Seaweed were alsogood to help to the balance of phytoplankton. Through the harvest of seaweed can successfully helptransfer nutrient from seawater and radically cut nutrient concentration in the marine environment,control the status of eutrophication. During bioremediation stage, G. chouae successfully transferred1.423kg of nitrogen and0.163kg of phosphorus. The seaweed culture should be expanded to2.87or5.37as lager as Initial scale, so as to reduce nutrient pollution caused by Sparusmacrocephlus culture.