| A series of environmental problems have been generated along with the social economydevelopment in Nansi Lake catchment, among which, the release of heavy metals and itsdeposition in the lake have attracted a great deal of world-wide attention. In this study, twohundred and five surface sediments samples and one continuous core were collected fromNansi Lake, and then the contents of eight metals (Cd, Cr, Cu, Hg, Ni, Zn, Pb and As) and itsfractionation were analyzed in order to investigate the typical heavy metals spatial distribution,sources identification, pollution assessment as well as the bioavailability. The main resultswere showed as follows:(1) The enrichment degree of studied metals decreased in the order of Hg> Cd> As> Pb>Cr> Ni> Cu> Zn, and the average content of Hg, Cd, As and Pb were2.87-,2.73-,1.95-and1.89-fold higher than their background values respectively. As we can see from the spatialdistribution maps of heavy metals contents, the contents of Cd and Hg in most parts ofDushan sublake and Weishan sublake even reached as high as3-5times than theirbackground values. High content of As which was above2.9times higher than thebackground values were found in the southeast of the Weishan sublake, and high contents ofPb, Cu and Zn which were above2.1,1.2and1.1times higher than their background valuesrespectively were all found in the south of the Weishan sublake. The west part of the Dushansublake also showed high contents of As, Pb, Cu and Zn.(2) Cd had the greatest water-soluble and exchangeable fraction per portion amongvalues of other metals considered, which showed the greateast bioavailability. The sumfraction of fraction bound to carbonate, humic acid fraction, reducible fraction and stronglyorganic fraction for As, Pb, Cu and Hg accounted for30%-50%, revealing greaterbioavailability, and the dominant fraction of Ni, Cr and Zn were the residual fraction (morethan70%of the total content), scarcely showing any toxicity to the environment.(3) Pollution degree of the metals and their potential ecological risk were definedreferencing to the pollution indices (geo-accumulation index, Igeo), the potential ecologicalrisk index for single regulators (E ir) and potential ecological risk index (RI) and the ratio ofsecondary phase and primary phase (RSP). The key monitoring area was also confirmed combined with ArcGIS9.3. Results showed that Cd got very close to and Hg was in moderatepollution. The priority regions of environmental monitoring and management areas wereobserved at most parts of Dushan sublake and Weishan sublake and the inflow areas ofDongyu River and Xizhi River. Most part of Dushan sublake and Weishan sublake even hadreached to considerable ecological risk state.(4) Statistical approaches (principal component analysis, PCA and hierarchicalagglomerative cluster analysis, CA) combined with spatial-vertical distribution of elementscontents in sampled core were employed to reveal the sources of elements. Results showedthat Fe2O3, Ni, Cr, Be, Li, V, Ti, Al2O3and partially Zn, Pb and Cu mostly originated fromnatural sources, while Hg, and partially Cd, Zn, Pb and Cu mainly came from metals miningand smelting, industry and traffic sources, and As and partially Cd, Zn and Pb representedagricultural activities like fertilising and pesticide consumption.In a word, the local government should take measures to control the pollutant emissioncontaining Hg, Cd, As, Pb and strengthen the monitoring and management of Dushan sublakeand Weishan sublake. At the same time, the local government should strengthen thesupervision of metals mining and smelting, industry and traffic activities and guide the localpeople use the pesticides and fertilizers in a scientific and reasonable way. |
