| The first-stage storage of the Three Gorges Project ended on the 10th June 2003. In order to investigate the influence of the Three Gorges Project on the Changjiang Estuary and adjacent area, two cruises were carried out in June 2003 and April 2007. Based on the collected data of heavy metal elements in the surface sediments, core sediments and suspended matter, the distribution and changes of heavy metals concentration were discussed. The pollution and potential ecological risk degree have been assessed using three methods. Combined with the 210Pb dating results, the contamination history and accumulation process of heavy metals were analyzed. The results show that:(1) The materials of Changjiang River was the main source of heavy metal elements in the surface sediments, and Changjiang Estuary can be regarded as the most important sediment sink in the early period after the first-stage storage of the Three Gorges Project (2003). However, Hangzhou Bay may had already replaced Changjiang Estuary to be the first sediment sink in April 2007.The concentration of heavy metals appeared a decreasing trend since the first early stage of the project.(2) According to the enrichment characteristic of heavy metal elements in mud area, the hydrographic dynamics and the absorption of fine-grained sediment (besides of the provenance effect) were found to be the main controlling factors on the distribution of the elements. From the accumulation of individual element (especially Cd) in the hypoxia-zone, it was obvious that redox environment also dominated the distribution of heavy metals. The order of adsorption and deposition by fine-grained sediments was Zn, Fe, Cr, Pb, Cu, Co, Cd (Ni).(3) The distribution characteristics of heavy metal elements , that high in the south and low the north, high in shore area and low offshore, high in mud area and low in sand area ( particularly in the northeast of study area) had no variety, revealing that the mechanism of sediment was unaltered.(4) Suspended matter concentration and salinity were found to be the main factors which controlled the accumulation of Cu, Co and Ni on suspended matter; direct discharge of industrial and municipal sewage affected the distribution of contents of Pb, Zn and Cd. Besides of lack of proportion in solid, transfer from suspended to liquid was another reason for the enrichment of Cd. Cu, Pb, Zn, Cd, Co and Ni had no relationship with temperature.(5) The number proportions of sediment samples with the concentration of Cu up to the second-class sediments standard have increased after the first-stage water storage of the Three Gorges Project, occasionally bringing adverse biological effect, Cr shows the opposite features. Whereas, the proportions of that of Pb, Zn and Cd in different sediments quality standards are relatively steady, rarely bringing about adverse biological effect.(6) In general, pollution extents and potential ecological risk were low in the study area. The pollution extents of typical pollutant is in the order of Cr>Cu>Zn>Pb>Cd and the potential ecological risk level of these heavy metals is as follows: Cd>Cu>Cr>Pb>Zn. Moreover, Cd and Cu were main factors of potential ecological risks in the research areas.(7) Compared to that before the first-stage water storage, potential ecological risk index and their risk level of heavy metals increase slightly in the early First-Stage Storage of the Three Gorges Project (2003), but the risk level in 2007 is similar to that in1988-1992.(8) There were three stages on the contamination history of heavy metals. The enrichment factor (EF) of heavy metal elements in the first stage (from the end of 1970s to the end of 1980s) were larger than the second stage (from the end of 1980s to begin of the 1990s), which was concerned with the success of soil and water conservation. The construction of the Three Gorges Project, the Catastrophic Flood in1998 and discharge of industrial and municipal sewage had resulted in the increasing of EF.
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