Distribution And Evaluation Of Heavy Metals In Coral Growing Regions Of The Northern South China Sea

The coral reef ecosystem plays a very important role in marine biodiversity protection,the maintenance of regional and global ecological health.With the intensification of human activities,coastal heavy metal pollution problems have become increasingly prominent and seriously affected the coral reef ecosystem health.This article focused on the analysis of the distribution characteristics and ecological risk of heavy metals(Hg,As,Cu,Cd,Cr,Pb and Zn)in the seawater,sediments and coral skeletons,the samples of which were collected from northern South China sea including Weizhou Island,Luhuitou in Hainan Islands,Dengloujiao in Leizhou Peninsula and the coral communities in Daya Bay in Guangdong province.The main research conclusions are as follows:(1)The average contents of heavy metals in the seawater of the 4 coral growth regions were 6.92(Zn),1.05(Pb),0.89(Cr),0.80(As),0.77(Cu),0.079(Cd)and 0.055(Hg)μg/L.The average contents of Pb and Hg were higher in Luhuitou and Dengloujiao than the other two regions and exceeded the First-Classed Seawater Quality Standard of China.In addition,the average content of Hg element in Daya Bay was beyond the First-Classed Seawater Quality Standard.The results of comprehensive index method(WQI)showed that:the WQI values of the 4 regions were less than 1,and the heavy metal content was in a low pollution level.(2)The average contents of heavy metals in sediments of the 4 coral growth regions were 15.55(Zn),8.15(Cr),5.66(Cu),3.75(Pb),3.14(As),0.07(Cd)and 0.06(Hg)μg/g.The contents of As,Cu,Cr,Pb and Zn in Dengloujiao region were significantly higher than those in the other 3 regions.And the contents of Hg and Cd in the 4 reef areas were basically the same.The contents of all the heavy metals did not exceed the First-Classed request of the marine sedimentary evaluation criterion.The potential ecological risk index(ERI)evaluation showed that:the ERI values of 4 regions were less than 150,which indicated that the potential ecological risk of heavy metals was at a low level.For the single element on the contribution rate of ERI,the comprehensive potential risk index contribution rate of Hg element were 69.14%,61.43%,76.28%and 56.55%in Weizhou Island,Daya Bay,Luhuitou,Dengloujiao.Therefore,Hg was the main potential risk factors.(3)In Weizhou Island,the average contents of heavy metals in 5 coral skeletons were 22.66(Zn),2.93(Cu),1.90(Pb),0.70(Cr)and 0.14(Cd)μg/g.In Daya Bay,the average contents of heavy metals in 10 coral skeletons were 34.77(Zn),6.02(Cu),2.29(Pb),1.50(Cr)and 0.16(Cd)μg/g.In Luhuitou region,the average contents of heavy metals in 9 coral skeletons were 22.66(Zn),2.93(Cu),1.90(Pb),0.70(Cr)and 0.14(Cd)μg/g.In Dengloujiao region,the average contents of heavy metals in 6 coral skeletons were 11.48(Zn),1.96(Cu),1.04(Pb),0.70(Cr)and 0.13(Cd)μg/g.Single factor analysis of variance showed that there was no significant difference between 4 heavy metals except Cd in Weizhou Island.There were no significant differences between 5 heavy metals in other 3 coral growth regions.This shows that the regional environmental conditions are important factors affecting the content of heavy metals in coral skeletons.The enrichment coefficient showed that the enrichment coefficient of Cu and Zn were higher in this 4 coral growth regions and lower enrichment coefficient of Cr.This indicates that the enrichment of heavy metals by coral was specifically selective.Through regional comparison,Cu,Cd,Cr,Pb and Zn content in coral skeleton were in latively low level in 4 coral growth regions.The content of Pb in Weizhou Island and Daya Bay was 4.5-13.78 times of that in the Great Barrier Reef,which should arouse more attention.(4)Heavy metals in the coastal coral growth regions of northern South China Sea may be mainly derived from industrial sewage,shipping,tourism,aquaculture and agricultural activities.