HISTORY OF HEAVY ELEMENTS IN THE LAST 250 YEARS RECORDED BY SEDIMENTS IN HUGUANG MAAR LAKE (HUGUANGYAN)

The Huguang Maar Lake(110°17'E,21°9'N) located in the southwest of Zhangjiang, Guangdong Province, belongs to the Leiqiong Volcanic Field. This paper is focused on the historic changes of heavy metals(V,Ni,Cu,Zn,and Pb) concentrations in sediments of the Huguang Maar Lake for the last 250 years. The environmental implication of heavy metals from core sediments was given by ¹³⁷Cs and ²¹⁰Pb isotope dating methods for the purpose of discussing the characteristic changes of heavy metals. Four stages of the heavy metal concentrations are recognized.Before 1880,concentrations of all heavy metals except V kept steady. From 1880 to 1920,concentrations of Ni, Cu, Zn and Pb increased, which could be related to the industrial development and the wars during the period. In 1920s the increase of Pb may reflect the wide use of Pb alkyl additives in gasoline. From 1975 to 1990, the content of Pb increased quickly mainly due to reform and opening-up, which caused the development of industry and transportation. The geo-accumulation index(Igeo) and the enrichment factors(EF) were used to assess their contamination levels. The results showed that the concentrations of V,Ni,Cu,and Zn were slightly influenced by human activities,and the Igeo and EF reveal that these metals were considered as "unpolluted to mild polluted". Pb was considered as "unpolluted to mild polluted" before 1920s and "moderately polluted" after 1920s.