Distribution Characteristics And Ecological Risk Assessment Of Heavy Metals In Seagrass Sediments In Caofeidian Sea Area,Tangshan

Seagrass bed ecosystem has important ecological functions and social and economic values,such as stabilizing sediment,purifying water,storing organic carbon,and mitigating wave impact.However,in recent years,various human disturbance measures have led to the aggravation of water eutrophication in offshore waters,and the gradual increase of heavy metals and other pollutants in sediments,which have brought many adverse effects to the seagrass bed ecosystem.Therefore,it is of great scientific significance to analyze heavy metal pollution in seagrass bed sediments for the protection of coastal Marine ecological environment and seagrass bed ecosystem.In this paper,the sediment of seagrass bed in Caofeidian Sea area was taken as the research object to analyze the physicochemical properties(electrical conductivity,p H,organic matter,total nitrogen,total phosphorus,particle composition)and the horizontal and vertical distribution characteristics of heavy metals(Cr,Ni,Cu,Zn,Cd,Pb)in sediments under different coverages.The influencing factors and possible sources of heavy metals in seagrass sediment of Caofeidian sea area were analyzed,and the pollution status and potential ecological risk of heavy metals in seagrass sediment were evaluated by various sediment pollution evaluation methods.The results are as follows:(1)With the increase of seagrass coverage in Caofeidian sea area,the p H,electrical conductivity and total phosphorus of sediment did not change significantly,indicating that the p H,electrical conductivity and total phosphorus were less affected by the seagrass coverage.The increase of seagrass bed coverage can promote the deposition of suspended particulate matter by inhibiting water flow,and the seagrass bed can also prevent the fine particulate matter in the bottom sediment from moving upward to the water body.The contents of organic matter,silt and clay tend to increase,while the contents of sand tend to decrease.Seagrass has a symbiotic nitrogen fixing system similar to that of terrestrial plants,which can absorb a large amount of nitrogen and phosphorus and other nutrients needed to maintain its own growth.The greater the coverage of seagrass,the higher the nitrogen content of seagrass sediment.In the vertical direction of 0~50 cm,with the increase of sediment depth,the roots of seagrass can secrete organic acids into the sediments,which can acidify the rhizosphere sediments,and the p H increases.The conductivity decreases gradually with the influence of the substrate itself.The organic matter decreased gradually due to hydrodynamic factors and the decaying and deposition of plant and animal remains such as seagrass beds in sediments.The sand content decreased and then increased,and the silt and clay content increased first and then decreased,which was mainly due to the large number of carbonate producing biomes on the seagrass leaves in the upper layer of seagrass bed,while the middle layer was fixed by the seagrass bed roots.Total nitrogen had no obvious change trend,while total phosphorus content increased first and then decreased.(2)The content of six heavy metals in seagrass sediments of Caofeidian Sea area was Cr >Zn > Cu > Pb > Ni > Cd.Among them,the content of Cd is higher than the local soil environmental background value,the soil background value of Hebei Province and the national "Marine Sediment Quality"(GB18668-2002)standard,the content of Cr,Zn,Cu,Pb and Ni heavy metals are all within the standard range.Cu and Zn decreased significantly with the increase of seagrass coverage,while the other four heavy metals showed no obvious change trend with the increase of seagrass coverage,indicating that the seagrass had strong absorption of Cu and Zn.The variation trend of heavy metal content in each site from the surface to the bottom showed little difference,which generally showed that the heavy metal content was lowhigh-low with the increase of depth,in the shape of ">".Correlation analysis results show that there is no significant correlation between heavy metals and physicochemical properties of sediments.Except Cu and Zn in sediments,there is no significant correlation between other heavy metal elements.The results of principal component analysis showed that the heavy metal pollution sources of Caofeidian seagrass bed sediments may be fisheries,oil exploitation,industrial production and shipping traffic.(3)According to the local environmental background value,the soil background value of Hebei Province and the first-class standard of Marine Sediment Quality,the evaluation results of heavy metal pollution in sediments show that the accumulation degree of Cr,Zn,Cu,Pb and Ni in the study area is light,while the accumulation degree of Cd is high.The study area is in the pollution level as a whole.The results of potential ecological risk assessment showed that the comprehensive ecological risk index RI value of six heavy metals in the sediment of seagrass bed in the study area ranged from 98.49 to 198.6,with an average value of 143.33.The seagrass bed area of Caofeidian belongs to the degree of slight ecological risk,and Cd is the main potential ecological risk factor of Caofeidian seagrass bed area,which needs to be paid more attention in the future.In view of the environmental pollution and ecological risk in Caofeidian seagrass bed region,this paper discusses the prevention and remediation measures of heavy metals in sediments combined with the local situation,which can provide reference for the prevention and remediation of heavy metal pollution in seagrass bed sediments.