The Determination Of Environmental Geochemical Baseline Of Heavy Metals In Surface Sediments Of Lake Taihu And Lake Dianchi

Lake Taihu in the Yangtze River Delta and Lake Dianchi in Yunnan-Guizhou Plateau was selected as study areas, and surface sediment geochemical baseline is our research object. We determined geochemical baseline values through several methods, including normalization method, relative cumulative frequency curves, iterative 2σ-technique and calculated distribution function (the latter three collectively referred to as statistical methods). In the same time, we expound main shows and main sources of regional differences using correlation analysis, cluster analysis and principal component analysis. As follows:Heavy metals in surface sediments of Lake Taihu mainly show a distribution of high in north and low in south, and Meiliang bay (1#) and Zhushan bay (6#) are the two most serious contaminated areas. In the whole lake of Taihu, As, Co and Pb are much more clear than other heavy metals while Cr, Cu, Ni and Zn are much more contaminated, and have a serious point source pollution. Heavy metals in surface sediments of Lake Dianchi are mostly polluted in inner Dianchi, mostly named Caohai, then the areas which are closed to Caohai. In the whole lake of Dianchi, Co and Cr are impacted by human being least while Cu, Ni, Pb and Zn are too high in Caohai and its surrounding area. In the same time, other place in Lake Dianchi, we can also see point source pollution.We use normalization method and statistical method to determine environmental geochemical baseline of heavy metals in surface sediments of Lake Taihu and Lake Dianchi. The results show that the different methods used to determine the geochemical baseline value have some difference. View from the comparison of different regions, baseline value of Lake Dianchi is higher than Lake Taihu, maybe it is regard to the difference of natural parent material and the uplift of overall pollution of Lake Dianchi. From a different point of view, each method has advantages and disadvantages, such as the normalization method is not suited to serious polluted region, while the relative cumulative frequency curves is suitable to regions which have significant point source pollution. The correlation between each two heavy metals of Lake Taihu and Lake Dianchi are significant differences, so as the Cluster Analysis. So it is necessary to analyze the regional differences in features. From the principal component analysis results, the origins of heavy metals in surface sediments can be classified as three main sources, one be considered as exogenous input of water pollution, the second be considered mainly natural source of parent material, the third be considered as sources of atmospheric deposition. However, for one particular element, the sources are not the same, such as As in Lake Taihu is mainly from natural source of parent material while in Lake Dianchi is exogenous input of water pollution.In summary, this thesis comprehensive compare the advantages and disadvantages of various methods which are used to determine the baseline value, then used in the practice of surface sediments of Lake Taihu and Lake Dianchi. We succeed in determined the baseline value of Stream sediment in the areas which have different regional characteristics. Our work can provide references to local policies and regulations makers and researchers, so our work has excellent practical value.