| Land-based pollutants,represented by heavy metals,inorganic salts and organic matter,are discharged into the nearby waters through river channels,bearing the brunt of the pressure on the marine water environment and fishery resources.With the increase of population and the advancement of industrial and agricultural production,the pollution produced is increasing.When land sources are discharged into the sea,exceeding the threshold of ocean self-purification capacity,it will lead to degradation of marine water environmental quality,such as eutrophication of water quality.and directly or indirectly contribute to the decline of biodiversity,threatening the original balance of marine ecosystems.In order to effectively control the effects of land-based pollution into the sea on marine ecosystems,it is necessary to carry out timely and effective monitoring and simulation prediction of the extent of pollutant severity into the sea,aiming to provide a basis for the planning of fishery resources in the area of discharge selogs into the sea.This paper selected the typical waters near the sea in Zhejiang into the sea as the research area-Ningbo City,Haihai District,Weijiang 4 sewage outlet,Taizhou City,the pepper river into the mouth of the two sewage outlets and Yuyao City Xiagai River 1 sewage outlet,the study area of the sea water quality carried out a status survey,found that the water quality near the sewage outlet has a certain degree of pollution impact,but the degree of pollution is small.On this basis,the mathematical model of flat two-dimensional currents was used to predict the diffusion of pollutants into the Qiantang River and Pepper River and the diffusion prediction of pollutants into the sea at the coastal sewage outlets of Yuyao and Pepper River.When it was found that the maximum diffusion concentration of pollution factorn N and COD increments was much less than the maximum diffusion concentration of the sewage of Qiantang and Pepper Rivers when it entered the sea,the influence of sewage on sea water quality was determined to be much less than that of the river sewage into the sea.In addition,in order to scientifically evaluate the impact of land-based sewage on marine ecology,this study collected the toxic data of related pollutants on aquatic organisms,and took into account that the main pollutants of heavy metal pollution caused by sewage discharge were copper,lead and chromium.Therefore,the most sensitive and insensitive marine life of copper,lead and chromium were selected for ecological risk assessment in the toxicity test,and the ecological risk coefficient was calculated according to the formula X1-EECmax/LC50.The results of the on-site survey showed that the environmental factors exceeding the fourth standard threshold of the Sea Water Quality Standard(GB3097-1997)were: heavy metals,active phosphates,petroleum and arsenic,and the distribution of excess pollutants in the three survey areas was different.The specific performance is as follows: 4 sewage outlets in Zhenhai District super four types of sea water quality pollutants are: heavy metals(mercury,cadmium,lead,chromium,copper),active phosphate,arsenic and petroleum;In addition,the concentration value of oil-based substances fluctuates most significantly with the change of diffusion distance.Among them,the distance with the sewage outlet within the scope of investigation is higher.In heavy metal elements,the nutrient salt is in the monitoring range,and its concentration value changes not significantly with the diffusion distance.The results of the assessment of ecological risk coefficient show that the nitrogen,phosphorus and COD emitted from the sewage discharge and the sewage mouth of Yuyao City and the sewage mouth of the Pepper River estuary are low risks to the ecology of the sea area. |
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