大亚湾扁脑珊瑚中重金属的年际变化及其海洋环境指示意义

通过对南海北部大亚湾海区1976～1998年扁脑珊瑚Platygyra骨骼Cu,Pb和Cd含量的研究及其与观测记录的比较,初步认为珊瑚可以记录大亚湾海区重金属的年际变化特征;发现1979年和1991年是重金属含量比较高的年份;由扁脑珊瑚记录推测珊瑚中Cd含量短时间内可能受到了核电站兴建的影响,但近20多年来的大亚湾扁脑珊瑚及海水中重金属状况的总体变化过程可能与整个广东海域水质的变化背景基本一致,而与核电站的兴建和运行似乎没有明显的关系

ANNUAL CHANGES OF HEAVY METALS IN CORAL PLATYGYRA IN DAYA BAY AND THEIR MARINE ENVIRONMENT IMPLICATION

Reef corals have proved to be good records of the past hundreds to thousands of years of envi ronmental history in tropical oceans. In China,some advances have been made on the calibration of coral skeleton ^δ18O,Mg/Ca,Sr/Ca,U/Ca and SST,of coral skeleton ^δ13C and sunshine duration,rain fall and cloud cover,in the past environment reconstruction,and in the climate event analysis,such as El Nio. But almost no study has been made on the heavy metal variations recorded in corals in the mainland of China,though many publications from international and Taiwan of China have made great contribution in this field. Daya Bay,located in the northern coast of the South China Sea,is the largest gulf aquatic products reserve of Guangdong Province. Many reef corals grow in the waters. The first nuclear power station of China,located in the southwest coast of the bay,came to build in 1986 and to run in 1994. So it′s an ideal site not only for studying heavy metal variations over past decades,but also for monitoring the influence of the nuclear power station on the waters. A coral sample Platygyra with about 20 years growth history was collected at 1.5m water depth and about 1.5km away from the thermal effluent outlet of the nuclear power station of Daya Bay in the October of 1998. After collection,it was soaked and washed with freshwater in order to eliminate the remaining portion of coral tissue or endolithic algae and salt. Then a 1cm thick slab was cut with a high speed diamond saw in the direction of the axis of major growth. Dry coral slabs were X radiographed in order to reveal the skeletal density banding pattern and determine the annual growth rates. Using the X ray negatives as a location guide,the sub annual samples were sliced or scraped with a very thin razor blade by hand with continued sampling resolution of 0.8 cm. A total of 38 samples were taken for cupper (Cu),lead (Pb) and cadmium (Cd) analysis. Each subannual sample was about 0.1～0.3g. The Cu,Pb and Cd were determined by means of polarography with precision of 5%～10%. The experimental results indicated that 1979 and 1991 were the two years of higher concentration of Cu,Pb and Cd,so this paper inferred that they were also the higher concentration periods of the waters of Daya Bay. The 1991 was proved to be a higher heavy metals concentration year by the "South China Sea Mussel Watch Program",which was carried out by using oyster Crassostrea rivularis to monitor Zn concentration in the important mariculture waters of Guangdong from 1989 to 1997;Because of no instrumental data or relevant record being found, cause of the 1979 of high heavy metal concentration year had not been discussed. Our results indicate that Cd was slightly influenced by the building of the power station,however,Cu and Pb were uninfluenced. Cu,Pb and Cd were not influenced by the running of the plant. Although the annual resolution carried out in this paper,however,the research could not rule out the possibilities of some accidental or shorter time scale pollution events,for example monthly pollution,because the shorter time pollution record was averaged to a low level by the annual sampling. By comparison with the heavy metals concentration from other areas,this paper suggested that the annual changes of heavy metals concentration in the Daya Bay was in general matching with the whole seawaters of Guangdong Province,and reef corals might be potential indicator of heavy metals pollution of Daya Bay waters. $$$$