Distribution Characteristics And Sources Of Heavy Metals In Surface Sediments From Offshore Aquaculture Areas Of Eastern Fujian

The coastal zone,a transitional zone between the shallow sea and land,is uniquely sensitive and fragile,and because of its superior geographical location and natural resource conditions,it has become a region seriously affected by human activities.As one of the typical coastal human activities,aquaculture is highly dependent on the aquaculture environment,and excessive heavy metal content in the environment will seriously threaten the biological quality and food safety.At the same time,some heavy metal elements will be released into the environment by aquaculture activities.This contradiction attaches value to the research on the status,distribution and source of environmental heavy metals enrichment in aquaculture areas.The largest marine aquaculture base in Fujian province—the Fujian east offshore aquaculture area,was selected as the research area to collect surface sediments from four typical aquaculture areas(Dinghai-Huangqi Bay,Luoyuan Bay,Sandu'ao,Dongwuyang).By measuring the particle size,heavy metal element content(V,Cr,Co,Ni,Cu,Zn,Cd,Pb),and non-heavy metal element content(Al),this research mainly explores the spatial distribution and its influence factors of heavy metals,the current situation evaluation of the enrichment in the surface sediments from offshore aquaculture areas of Eastern Fujian.Based on GIS spatial analysis,enrichment factor method,and multivariate statistical analysis,this study figures out the source of heavy metal pollution in east fujian offshore aquaculture area.The conclusions are as follows:Firstly,the grain size characteristics of surface sediments in the eastern Fujian offshore aquaculture area show that the sediments are mainly silt(4-63)and clay(<2),which accounts for 60.80% and 29.59% of the sample size composition on average.The particle size of the sediments in each aquaculture area increased from Dongwuyang,Luoyuan Bay,Sandu'ao to Dinghai-huangqi Bay,whose main reason is the difference of regional tidal current hydrodynamic strength caused by the bay morphology and geographical location.Secondly,the average contents of V,Cr,Co,Ni,Cu,Zn,Cd,and Pb in the surface sediments from the eastern Fujian offshore aquaculture area are: 104.97mg/kg,80.81mg/kg,16.24mg/kg,37.58mg/kg,30.17mg/kg,131.93mg/kg,0.10mg/kg,37.59mg/kg,all exceeded the background value of shallow coastal sediments in Fujian,reaching a certain cumulative level.Among them,Cr,Cu,and Ni are at higher enrichment levels,and in combination with the offshore geological background of eastern Fujian,it is believed that this may be related to the regional high background value caused by the widespread distribution of basic rock in eastern Fujian.Regarding the distribution characteristics of elements in each aquaculture area,the distribution characteristics of other elements except Cd in each aquaculture area are significantly related to the distribution of clay,and show a higher content distribution at weaker hydrodynamic areas such as the bay top and intertidal zone.And the distribution of Cd is significantly different from other elements,mainly showing relatively low values in areas with variable sedimentary environments,such as intertidal zones,thus it is speculated that its distribution characteristics are mainly affected by the redox conditions or occurrence forms of the sedimentary environment.On this basis,various elements also have significant enrichment near industries,settlements,wharfs,cage culture areas,and aquaculture ponds in coastal areas.Among them,cage culture and pond culture,due to needing for artificial feeding bait,fish medicine and the disinfectant,have obvious endogenous pollution emissions,while the algae and shellfish aquaculture area mainly using raft and rope type free-growing without obvious pollution.Besides,the potential ecological risk assessment shows that in the surface sediments of eastern Fujian offshore aquaculture area,except for Cd,which is generally at a medium ecological risk level,all the other elements are at slight ecological risks,and the potential ecological risks of the region are mainly contributed by Cd.In addition,in the four aquaculture areas,except for the areas with significant impacts of individual point pollution sources along the coast,which show strong comprehensive potential ecological risks,the main breeding areas are all at medium ecological risk,and the low comprehensive potential ecological risk in the local areas can be considered to be related to the complex and changeable sedimentary environment and the higher proportion of coarse particles in the sediment without obvious impact of pollution sources.What's more,based on the spatial analysis of GIS,combining with enrichment factors and multivariate statistical methods,it is concluded that the surface sediments from offshore aquaculture areas of Eastern Fujian are generally affected by natural weathering of rocks and crust,industrial sewage,shipping and maintenance,and domestic sewage discharge sources.Moreover,Luoyuan Bay,Dongwuyang and Sandu'ao have also been affected by endogenous pollution from aquaculture.Among them,the V in the four breeding areas came from natural sources,and Cr,Co,and Ni were affected by industrial pollution on the basis of the general influence of natural sources,but the sources of Cu,Zn,Cd,and Pb were more complicated,whose main sources of pollution are different in different breeding areas.