Study On The Characteristics Of Pollution Diffusion And Its Impact On Ecological Sensitive Areas In Qinzhou Bay,Guangxi

The ecological environment of the Beibu Gulf in Guangxi is excellent,and it is one of the few "clean seas" in China.According to the "2021 Guangxi Zhuang Autonomous Region Ecological Environment Status Report",the overall water quality of the nearshore waters in Guangxi is "excellent".The excellent ecological environment has also given birth to abundant ecological resources.Many ecological sensitive areas are distributed in the Qinzhou Bay,such as the marine aquaculture area and mangrove ecological area.With the rapid development of the coastal economy in Qinzhou Bay,a large number of port logistics,steel,and petrochemical projects have gathered in the coastal areas,resulting in severe environmental pollution.The pollution of Qinzhou Bay’s seawater is on the rise,seriously affecting the ecological environment of sensitive areas and restricting local economic development.Therefore,in order to better analyze the current water quality pollution status of Qinzhou Bay and protect sensitive areas,this paper analyzes the water quality pollution status,pollution diffusion characteristics,and environmental capacity of Qinzhou Bay,providing scientific basis and theoretical reference for the protection of sensitive areas and the development of coastal economy.To understand the changes in water quality in Qinzhou Bay over the past decade,this paper analyzes the characteristics of water quality changes in the first ten years of Qinzhou Bay and provides background values for subsequent environmental capacity assessments.At the same time,this paper analyzes the tidal flow characteristics,pollution diffusion characteristics,and residual environmental capacity of Qinzhou Bay by constructing a two-dimensional hydrodynamic model and material transport diffusion model of Qinzhou Bay.The main research contents of this paper are as follows:1.The analysis of the current and planned shoreline tidal flow movement forms in Qinzhou Bay shows that the flow velocity near the Longmen Waterway and the east and west sides of the Sandun working area has significantly increased,and the ebb flow velocity is greater than the flood flow velocity.The residual flow of the inner bay below the current shoreline of Qinzhou Bay is generally weak,while that of the outer bay is generally strong.The Longmen Waterway is the area with the strongest residual flow,with a maximum of 0.225 m/s.The residual flow intensity of the outer bay below the planned shoreline of Qinzhou Bay is larger than that below the current shoreline,and the residual flow direction has changed.Under the action of wind,the overall residual flow intensity of Qinzhou Bay is enhanced,and the direction2.will also change.3.According to the marine survey data of Qinzhou Bay from 2011 to 2021,the concentration and average content of COD,DIN,and DIP in the Qinzhou Bay waters from 2011 to 2021 mostly meet the second-class water quality standard for seawater,and the indicators of COD,DIN,and DIP in the Qinzhou Bay waters from 2011 to 2021 comply with the corresponding marine functional zoning,indicating that the water pollution level is low.4.Based on the numerical simulation results of the A2 discharge outlet under different source strengths and wind conditions in Qinzhou Bay,after fifteen tidal cycles,the pollutants diffuse to all sensitive areas in Qinzhou Bay,and the water quality level in the discharge mixing zone does not meet the water quality target in the "Adjustment Plan," but the pollutant concentration in the sensitive area meets the water quality target.After being discharged from the A2 discharge outlet,pollutants spread in the direction of the Maowei Sea and the mangrove ecological area of the Jingu River under the rising tidal flow and in the direction of the Sandun working area under the falling tidal flow.Under the action of wind,the range of pollutant diffusion is larger than that without wind,but the pollutant concentration is lower.5.Under the future planned discharge volume,the water quality level in the discharge mixing zone of the A4 and A17 discharge outlets does not meet the water quality target in the "Adjustment Plan." The addition of wind and degradation coefficient in the water quality prediction model can effectively reduce the pollutant diffusion concentration.In addition,to better serve local economic development and protect the ecological environment of Qinzhou Bay,this paper also simulated and predicted the simultaneous discharge of the A1,A2,A4,and A17 discharge outlets and calculated the maximum discharge volume that meets the water quality target,which are 2.8936 m3/s,2.2310 m3/s,2.3212 m3/s,and 0.7765 m3/s,respectively.The research results of this paper can provide scientific basis for the environmental capacity assessment,pollutant discharge control,and balanced development of the economy and environment in Qinzhou Bay,and play a promoting role in the sustainable development of the marine economy in Qinzhou Bay.In addition,it also provides reference for the protection of the national marine ecological environment and the layout of offshore productivity.