The Research Of Typical Heavy Metals Pollution In Sediments From Dongping Lake

With the rapid development of economy, the lake ecosystem is under increasing pressure, and the water environment is deteriorating, which has affected human production and living activities. Dongping Lake is one of the most important water sources in the southwest of Shandong Province, and serves as the last reservoir along the Eastern Route of China's South-to-North Water Diversion Project. From this perspective, Dongping Lake has an important geographical position and strategic significance. In this study, several surface sediment samples and columnar cores were collected from Dongping Lake through a deep investigation, and then the concentrations of eight heavy metals were analyzed, including Cd, As, Hg, Pb, Cu, Zn, Cr and Ni. The specific research contents and results were as follows.(1) The average concentrations of all metals were higher than their background values, especially Cd, As and Hg, which were 3.7, 3.4 and 3.7 times their background values, and had strong ability of enrichment in sediments from Dongping Lake. The concentrations of Cu, Cr, Ni and Zn were equal to their background values, and had low degree of enrichment in surface sediments. Comparing the concentrations of heavy metals with the values of SQGs, we could see that 89% for As fell in the range between TEL and PEL, and the concentrations of As in 11% of the samples were higher than PEL. That is to say, adverse biological effects might be made by As in sediments from Dongping Lake.(2) The spatial distributions of As, Hg, Cu, Pb, Cr, Zn and Ni showed roughly similar changing trends, with concentrations decreasing from southeast to west progressively, which might be primarily affected by the infusion of the branch in the southeastern of Dongping Lake. While Cd showed a little different trend from others, with values decreasing from both sides of north and south to the middle of the lake.(3) The results of geochemical speciation analysis showed that Cd had higher concentrations in carbonate fractions, which account for 24%. The proportion of non-residual fractions is higher, showing that Cd has been greatly influenced by human activities. Others were mostly locked up in residual fraction, which account for over 50% of the total. The maximum values of residual fraction appeared at C4, while the minimum values appeared at C2, except Cr and Zn.(4) The potential ecological risks of heavy metals in sediments were assessed by EF, PERI and REP. The results showed that the whole Dongping Lake was in considerable risk, and Cd might lead to high potential risk with high enrichment degree. Hg and As were in moderate risk, while others had little effect to the environment.(5) The results of correlation analysis, CA and PCA were consistent, and the sources of heavy metals were roughly divided into three categories. Cr, Zn, Ni and, partially, Cu mostly originated from natural sources; As, Hg, Pb and, partially, Cu represented industry and mining sources; Cd mainly originated from agriculture sources. The industry and mining pollution was mainly distributed in the southeast of Dongping Lake basin, with some industries in the southeast basin, including power plants, chemical plants, mechanical manufacture factory and so on. In addition, Dawen river flows into Dongping Lake carrying a lot of industrial waste water, which made great contributions to the concentrations of As, Hg, Pb and Cu. Large areas of agricultural land is distributed in the west and south basin of the lake, leading to serious agricultural non-point pollution.