| At present,coral reefs have suffered serious degradation worldwide,and heavy metal pollution is considered to be one of the causes resulting in coral reefs decline.This study tested 67 seawater samples,29 surface sediment samples and 40 coral skeleton samples in Zhongsha and Xisha Coral Reef District of the South China Sea to study the content and distribution characteristics of heavy metals.Weights modified Nemerow pollution index method,Potential Ecological Risk Index Method and Enrichment Factor method were used to assess the heavy metal pollution in coral reefs and to discuss the ecological impact of heavy metals on coral reefs.The main conclusions are as follows:1.Heavy metals content:Atomic spectrophotometry(Cu,Pb,Zn,Cd,Cr)and atomic fluorescence spectrometry(As)were used to determine heavy metals in surface water of coral reefs.The average contents were 1.309(Cu)?1.702(Pb)?2.831(Zn)?0.056(Cd)?0.202(Cr)?0.272(As)?g/L,respectively,and only Pb exceeded the First Class Seawater Quality Standard of China.The contents of Cu,Pb,Zn,and Cd in surface sediments were determined by atomic absorption spectrophotometry and the average contents were 0.463(Cu)?0.602(Pb)?5.201(Zn)?0.027(Cd)?g/g,all falling within the national marine sediment quality standard and background value of South China Sea.Inductively Coupled Plasma Mass Spectrometry(ICP-MS)was used to determine the content of Cu,Pb,Zn,Cd,and Cr in coral skeletons.The average contents of heavy metals in coral skeletons were 1.05(Cu)?1.02(Pb)?2.34(Zn)?0.03(Cd)?1.11(Cr)?g/g.2.Spatial distribution of heavy metals and possible influencing factors:The average heavy metal content in the reef area of Xuande Archipelago in the Xisha Islands was higher than that in the Yongle Islands,indicating that in recent years,human activities,such as reef construction,had affected the water quality in Xuande Islands,especially the Yongxing Island.Heavy metal content in the seawater of Huangyan Island in the Zhongsha Islands is relatively high among the nine reef areas,because it is located in the necessary navigational routes between the South China Sea and East Asia,and often affected by the pollution from ships such as sewage and tail gas during the operation of fishermen.Heavy metals in coral skeleton in 2m water depth were higher than those in 15m water depth,suggesting that heavy metals in coral skeleton are derived from surface water.In addition,the distribution of Zn in the entire coral reef area is affected by the input of terrestrial sources,and the distribution of Pb has a significant relationship with the atmospheric deposition.3.Possible ecological effect:Weights correcting Nemero pollution index(NI)of seawater is at the assessment level ?,a relatively clean level,while the NI of Beijiao has reached Level ?,a light pollution level.The content of Cu in seawater is close to the bio-safety concentration of corals,which may have a negative effect on the growth of corals in the future.The integrated potential ecological risk index(RI)of surface sediments is at a low risk level,but the RI values of the North Reef and the eastern Xisha Reef areas are relatively high,indicating that these areas have certain potential ecological risks due to human activities.The contribution rate of Cd to RI in surface sediments is more than 80%,indicating Cd is the main ecological risk factor in surface sediments.4.Enrichment capacity of coral skeleton to heavy metals:The coral skeleton enrichment coefficients are calculated for the Favites abdita,Pocillopora verrucosa,Coeloseris mayeri,and Goniastrea pectinata.The results showed that there is significant difference between different coral species.The enrichment factor of element Cr in these four corals is the highest,and the enrichment coefficient of Cd and Zn is the lowest.For the same species of heavy metals,the enrichment ability of the Pocillopora verrucosa to Cr,the Coeloseris mayeri to Cu,the Favites abdita to Pb and Zn,and the Goniastrea pectinata to Cd is the strongest. |
PDF Full Text Request