Characteristics And Significances Of Trace Elements In Rivers Flowing Into Taihu Lake

In China, Taihu lake is an important lake in the Yangtze delta where there is the area of developed economy and dense population. The water pollution of Taihu Lake has directly influenced on the economic development of the middle-big cities like Shanghai, Wuxi, Suzhou. Because of the rapid development of industry and agriculture, and being short of environment protection and measures of preventing the pollution in those areas, the water quality of Taihu Lake has become increasingly worse and turned into the important factors of impeding the economic and social development during the past two decades. In this dissertation, the samples of water and sediments were collected in seven rivers which flow through Wuxi, Wujin district of Changzhou, Yixing and enter into the Taihu Lake. Then, the characteristics of trace elements in water and sediments were analyzed, which could provide the information about solving the river pollution. Indications and environmental significances about trace elements in rivers were exploited in the research areas.The contents of trace elements in water and sediments were detected and calculated firstly. The characteristics of heavy metals were analyzed and those contents in water and sediments were compared with the standards of surface water and the soil background values respectively. It was found that Zn, Pb, Cu, Ni, Cr had been changed greatly by anthropogenic activities, but Cr in some degree, V basically not. The differences of the contents of dissolved heavy metals between seven rivers were not very much, but Zn in Xiwan River was very low. Among of all elements, Ni had the highest content in rivers. This point was different from that in sediments. The contents of heavy metals in sediments varied greatly in rivers, whose ranking of variation coefficient were Zn>Pb>Cu>Cr>Ni>V>Co. In seven rivers, Pb had the highest enrichment degree, others were ranked as follows Cu>Zn>Ni>Cr, but Co and V were depleted. According to thestandard of ecological qualities, it could be induced that the four metals of Zn> Cu> PtK Cr had high ecological risks. Viewed from the whole, the most part of the research areas had been polluted by heavy metals which mainly included Zm Pbs Ok Ni, and slightly Cr.Viewed from the trace elements along each river, it showed that those differences were great in different sites. The locations of high contents of trace elements were generally near the districts where there were dense population, developed industrial factories or outlet of wastewater in cities or towns. There are some rules that the contents of several heavy metals show a figure of parabola along Wujin River, Caoqiao River and Liangxi River. It is apparent that the middle of those rivers have been mostly affected by industrial and living sewage caused by human. Therefore, anthropogenic activities, especially the industrial discharge and living sewage in towns or cities have a considerably influence on elements in rivers.Doing the principle component analysis with three representative rivers, it was concluded that Caoqiao River was polluted mainly by industrial pollutants;Dapu River were major in non-point pollutants, including somewhat industrial pollution;Liangxi River were the river polluted mainly by living pollutants with slight industrial pollution.According to the geochemical characteristics of various elements and those different ratios, it can be included that Zn/Fe^ Fe/Mg> Pb/Fe^ K/Ca, Mg/Al could be used to distinguish the rivers which flowing into Taihu Lake polluted by different sources. At the same time, the molar ratios of metals can also provide the method to differentiate the polluted sources. The molar ratios of metals about water or sediment in seven rivers concerned can be divided, that's to say, Caoqiao River and Mashan River belong into the same type, as well as Liangxi River and Xiwan River, but Dapu River is other type. They represent rivers polluted by industry, living and farm respectively. Therefore, some molar ratios can indicate the polluted sources effectively.Affected by human activities, the contents of REE in rivers flowing into Taihu Lkae varied greatly in a relatively short distance. The REE shale-normalized patterns of water were different from those of sediments. The water was HREE enrichment, while the sediment showed flat normalized REE patterns. What's more, Eu and Ce in water wereenriched obviously while they in sediment have enrichment and depleted. Because of the differences of polluted sources around the rivers, the total contents and normalized patter of REE were obviously different. River polluted mainly by industrial pollutants show MREE enrichment and obviously positive anomalies of Gd;river polluted mainly by domestic sewerage show HREE enrichment and obviously positive anomalies of Eu;non-point polluted river show flat normalized REE pattern and the content of La is high.In conclusion, different rivers display the different polluted degrees of heavy metal and trace elements vary largely in places seriously affected by human activities. By analyzing and comparing the ratios of some trace elements and the REE characteristics, we can indicate the nature of the polluted materials in different rivers. It is greatly useful for the the Yangtze delta basin where its economic have well developed and exist river network.