Analysis On The Distribution Characteristics And Influencing Factors Of Sediment Heavy Metals In The Lower Reaches Of Liao River And Its Estuary

Strong human activities in the river basin have increased the input of point source and nonpoint source pollution,affecting the output and transport process of nutrients,heavy metals and other substances.Natural water bodies enter the sea through the river basin and estuaries,which also poses a serious threat to the marine ecological environment.The distribution,transport,control and regulation of pollutants in the river basin offshore estuaries have become an important task for the country to coordinate the land and sea ecological environment protection in the new era.Among them,the land sea distribution and coevolution relationship of pollutants is the key content of formulating the management and control of pollutants in the offshore environment.At present,there is a lack of systematic research,which has brought great uncertainty to the offshore environmental governance.Based on this,this paper selects the Daliao River Basin,Shuangtaizi River Basin,Offshore Coastal-estuary area as the study area,selects 28 representative points(18 in the land and 10 in the sea)from the river mainstream and coastal estuary,and takes the conventional heavy metals As,Cu,Pb,Cd,Cr,Zn,Mn and Ni in the sediments as representative pollutants.The investigation and analysis will be carried out in September 2019,June 2020 and April 2021 to reveal that spatial and temporal distribution characteristics of heavy metals in sediments during wet,normal and dry season and their coevolution in river basin and offshore estuary;Based on this,the ecological risk and pollution degree of different heavy metals in rivers and estuaries are assessed,and the impact of human factors on the distribution of heavy metals in sediments is further analyzed,so as to provide scientific and technological support for the ecological environment treatment and protection of river basins and offshore estuaries.The main research results are as follows:(1)Spatial and temporal distribution characteristics of heavy metals in sediments.The contents of heavy metals Cu,Pb and Zn in sediments did not exceed the standard in the three observed hydrological periods,while the heavy metal Ni exceeded the standard seriously in each period,mostly concentrated in the Daliao River Basin.The exceedance of other indicators under different hydrological conditions is different: there are exceedance points for Cd in high water period,as,Cr and Mn in normal water period and low water period,and there are 27 sampling points for Cr in low water period.In the wet season,the contents of heavy metals As,Cd Cr and Ni are higher in the offshore area,and the contents of heavy metals Cu,Pb and Zn are higher in the Shuangtaizi River Basin;In normal season,the contents of heavy metals As,Cu,Pb,Cd,Zn,Mn and Ni in Daliao River Basin are higher,and the contents of heavy metal Cr in offshore area are higher;In the dry season,the contents of heavy metals As and Cd are higher in the offshore area,and the contents of Cu,Pb,Cr,Zn,Mn and Ni are higher in the Daliao River.The content of heavy metals in the samples collected in the dry season is higher than that in the normal season,and higher than that in the wet season.(2)Quantitative analysis on ecological risk and pollution degree of heavy metals in sediments.The assessment results based on the single factor pollution index show that Ni presents a heavy pollution level in the wet season and Cr presents a moderate pollution level in the dry season.In addition,all sampling points of heavy metals in the sediments in the three hydrological periods are at a pollution-free level;The evaluation results based on Nemero index show that each point is at level IV moderate pollution level in wet season,while each point is at level II warning level in normal and dry seasons;The evaluation results based on geological accumulation index show that the average value of Cr index in dry season is in level II unpolluted-moderately polluted state,and Ni pollution is more serious in wet season and normal season;The evaluation results based on pollution load index and potential ecological risk index show that all the points are in a non-polluted state and at a slight risk level under the three hydrological conditions.(3)Source analysis of heavy metal pollution in sediments.Based on correlation analysis and cluster analysis,it is clear that Cu,Zn and Mn come from the same pollution source;By comparing the distribution characteristics of human activities and heavy metals,it is clear that the urbanization level is related to the content of heavy metals As in the watershed,the content of As,Cu,Mn is related to the development of the tertiary industry,and Cu,CD,Zn is related to the level of industrial development;The application of agricultural chemical fertilizers is an important source of Cd,Cr,Pb,and the use of pesticides is an important source of Cu and Pb;In addition,traffic development,land use types such as towns and paddy fields are also factors affecting the content of heavy metals.