南海中沙群岛、西沙群岛珊瑚岛礁区海水重金属的分布特征

Distribution Characteristic of Heavy Metals in Coral Reefs Located in the Zhongsha Islands and Xisha Islands of South China Sea

基于2015年夏季对中国南海中沙群岛的黄岩岛和西沙群岛的永兴岛、七连屿、东岛、浪花礁、北礁、华光礁、盘石屿、玉琢礁等9个岛礁区的综合科学调查和采样,重点研究了重金属元素在礁区海水中的分布情况。结果表明:1)中、西沙海域的这9个岛礁区海水中重金属铜、铅、锌、镉、铬、砷的平均质量浓度分别为1.309、1.702、2.831、0.056、0.204、0.272μg/L,重金属整体水平较低,并以锌、铅、铜为主,质量浓度达所测重金属元素总量的92%,仅部分站点的铅元素质量浓度高于国家一类海水水质标准。2)在分布上大致呈现东部岛礁区高于西部岛礁区的特点,环礁潟湖与礁坡的海水重金属含量具有差异性,礁坡水体的铜、铅、锌、镉含量均高于潟湖,砷低于潟湖,这种差异可能与潟湖水体相对封闭有关。3)影响中、西沙岛礁区海水重金属分布的环境因子,主要包括陆源输入、大气沉降、环流等,其中陆源主要影响锌,大气沉降对铅作用明显,环流影响局部水平。4)采用权重修正内梅罗污染指数进行水质综合评价,得出中、西沙岛礁区域总体处于较清洁水平,海水重金属含量没有达到影响珊瑚生长的水平,但是铜元素对珊瑚的生长可能存在潜在危害。

Heavy metal pollution provides potential risks to the growth and development of corals. In recent decades, the coral reefs of South China Sea have been degraded as a whole, but the research on heavy metal pollution in such areas is scarce. This study was based on the integrated scientific survey and sampling on the nine selected coral reef areas of South China Sea in the summer of 2015, including Huangyan Island of Zhongsha Islands, Yongxing Island, Seven Lantau Island, Dongdao Island, Langhua Reef, Beijiao Reef, Huaguang Reef, Panshi Island and Yuzhuo Reef of Xisha Islands, and then focused on the distribution of the heavy metals in the seawater of those reefs. Our results indicated that： 1） The average concentrations of heavy metals in the seawater of the nine coral reef areas were 1.309, 1.702, 2.831, 0.056, 0.204 and 0.272 μg/L, respectively, for Cu, Pb, Zn, Cd, Cr and As. It meant that the overall level of heavy metals was relatively low, and Zn, Pb and Cu were the main contents of the total heavy metals, whose amount could be up to 92%. Besides, in some part of the sites, the content of Pb was higher than those of the First-Classed Seawater Quality Standard of China. 2） Generally, the distribution of heavy metals at the eastern reefs was higher than that at the western reefs. Furthermore, the content of heavy metals differed in atoll lagoon and reef slope, and Cu, Pb, Zn and Cd at reef slope were higher than in atoll lagoon, while As lower. The difference might be related with the relatively closed water in atoll lagoon. 3） The environmental factors, which affected the distribution of heavy metals in seawater in the coral reef areas of Zhongsha and Xisha Islands, mainly included terrestrial input, atmospheric deposition, ocean currents and so on. Thereinto, the terrestrial input principally influenced the amount of Zn, and the effect of atmospheric deposition on Pb was obvious, and ocean currents affected the local level. 4） Water quality was evaluated by the method of weighting-factor modified Nemerow index, which turned out the seawater was clean in Zhongsha and Xisha Islands. The content of heavy metals in seawater was not up to the level of affecting the coral growth except Cu element.