Research On Numerical Model And Environmental Impacts Of Scallop Cultivation In Jiaozhou Bay

Aimed at the hot point of the eutrophication of culture water and according to the field surveys in the Jiaozhou Bay and the research on dynamic model, the distributions and variations of DIN and DIP, controlling mechanisms and the influences to environment are analyzed in this thesis, and the ecological regulation of the Co-culture of Shellfish and Seaweed to water environment is also preliminary discussed. This research would give some necessary scientific foundations for the research on the environmental capacity of scallop cultivation in Jiaozhou Bay and the main research works and conclusions are listed as follows:Based on the surveys of the cultivated water in Jiaozhou bay in Nov. 17, 2004, the horizontal distributions of environmental parameters are analyzed, and the impacts of scallop cultivation on water quality in harvest time are preliminary discussed. The concentrations of COD, NH4-N and PO4-P inside raft culture area are higher than outside in surface water in Jiaozhou Bay, but no obvious variations in nitrite between culture and non-culture area. The dissolved oxygen content in bottom water and sulfide content in sediment inside culture area are seriously higher than the marine aquaculture standard. The average values of ammonia, nitrite and phosphate are 0.0592 mg·l-1, 0.0295 mg·l-1 and 0.0173 mg·l-1 respectively. Therefore, the environmental effects of scallop cultivation are comprehensive in harvest time, but only exist nearby the cultivation area.Princenton Ocean Model is applied to Jiaozhou Bay in order to provide the physical parameters for the study on the distributions of DIN and DIP and environmental effects. The model results show that the character of tidal current in Jiaozhou Bay is go-back flow and that Yellow Sea water enters Jiaozhou Bay from the northeast at maximal speed of about 0.73 m·s-1 at the channel and leaves Jiaozhou Bay from the northeast at about 0.79 m·s-1. The residual current of Jiaozhou Bay is controlled by four residual eddies. Based on the three dimensional simulation of tidalcurrent. A three dimensional pollutant transportation and diffusion model is established and applied for simulating the distributions of DIN and DIP caused by the major rivers in Jiaozhou Bay. The simulated results agree well with the observed data in the field, implying that this water quality model is reasonable and can provide the analyzable foundations for the environmental effects of scallop cultivation in Jiaozhou Bay.Based on the analysis of environmental impacts of scallop cultivation, the estimation of DIN and DIP pollution loads in scallop cultivation is improved and calculated in Jiaozhou Bay. Then, the three dimensional pollutant transportation and diffusion model is used to simulate the distributions and variations of DIN and DIP caused by the scallop cultivation in Jiaozhou Bay. The results show that the values of DIN and DIP caused by the scallop cultivation are only 8% of that from the rivers in Jiaozhou Bay, but the concentrations of pollutants in culture areas are clearly higher than that of the central and the channel areas. So, the scallop cultivation can bring the serious environmental effects in local culture areas.In the final part of this work, two numerical experiments are conducted focusing on the improvements to environmental effects of scallop cultivation. The results show that when the culture density is the half of the former values, the distributions of DIN and DIP caused by the scallop cultivation in Jiaozhou Bay do not change clearly, but there are almost a drop in the concentrations by half. The reduction in the culture density is very effective in improvement to the eutrophication level of local culture water. If the kelp is introduced the scallop cultivation system, the content of DIN would decrease about 20%. Therefore, the kelp cultivation after the harvest of scallop can effective reduce the content of DIN.