Effects Of Raft Aquaculture On Dynamics And Phytoplankton Ecosystem

Gouqi Island is the main sea mussel raft culture area of Zhejiang Province. With the increasing needs of high quality aquatic products, the mussel farming area of Gouqi Island has been troubled since 2003. The expansion of farming area result of increasing of culture facilities and mussels, which slow down the surface current around the sea area of Gouqi Island, thus weaken the sea water exchange capacity, reduce the breeding area within the phytoplankton update. Further more, mussels feeding progress on phytoplankton decrease the phytoplankton biomass in surface water, which has great influence on the phytoplankton ecology system.In order to explore the impact of breeding activities of Gouqi Island on water hydrodynamic and phytoplankton, we conduct a co ntinuous observation of chlorophyll a concentration, nutrients and current rate profile inside and outside farming area. There is significantly different between inside and outside area of current speed profile structure and chlorophyll a concentration structure, which is resulted from both the barrier of culture facility and the mussel farm and the feeding of mussels on phytoplankton. The chlorophyll a concentration inside the breeding area is higher than the outside area. The surface layer of inside breed ing owns the highest chlorophyll a concentration, while the middle layer of outside area owns the highest one. Outside the mussel breeding area, the maximum current speed appeared in the near surface water, and the maximum current speed inside the breeding area appeared in the midle-bottom layer. The effect of aquaculture activities on the water body and the consumption of the cultured organisms can not be ignored. Basing on observations and the results of previous studies, we select the resistance parameters to simulate the hydrodynamic of Gouqi island, involving the surface friction layer caused by culture activities to ECOMsi ocean numerical model. Focused on analysis the difference between hydrodynamic with surface friction layer and that without surface layer. The surface friction attenuate the surface velocity obviously between 20% and 90% inside the culture area. The velocity of middle layer attenuate weakly between 10% and 20% inside the culture area. The velocity of bottom layer is not mainly attenuating and increase about ten percent. The vertical law of the velocity in the culture area was significantly different from that in the open sea. The surface velocity was much lower than that in the middle and bottom waters. In addition, when the surface friction layer is added, the tidal ellipse in the sea area appears deformation in some way, while the internal tidal ellipse appears apparently deformation.Based on established three-dimensional hydrodynamic numerical model, coupling with attenuation of surface of the tracer model simulation mussel culture consumption of water in food(phytoplankton), we derived the space distribution of Gouqi Island sea area code spring and neap tide period averaged tracer concentrations, focusing on analyzing the di fference between surface friction layer and no surface friction layer. The existence of surface friction layer influence surface of tracer concentration level seriously. In this situation in the smaller neap tide is more obvious. The friction layer will strengthen the mixing of the surface water and the middle and bottom layers. Under the condition of the current distribution pattern of the cultivated area, the concentration of the tracer in some areas of the culture area will be very low. To a certain extent, it is reflcted that the pattern of mussel culture is not reasonable in the landscape of the Chinese wolfberry, and the pattern of the culture needs to be further optimized.Based on established three-dimensional hydrodynamic numerical model, coupling with NPZD ecological model simulated the mussel culture consumption of water in food(phytoplankton). The model simulated the filtering phytoplankton of mussel well. The chlorophyll a content of mussel culture area was significantly lower than that outside the farming area, about 1/2 of the outside the farming areas. The mussel culture influenced 0- 5 m of the surface waters inside the farming areas. The ecological model of this paper is preliminary. The parameters of the ecosystem model needs to be further optimized. This paper will further optimize the simulation in the next, and further amendments to the paper.