Speciation Distribution Of Elements And Its Responds To The First-stage Storage Of The Three Gorges Project In Sediments From Changjiang Estuary And Its Adjacent Sea Area

Changjiang estuary is the largest estuary in China, where land-sea interaction is significant, human activity is frequent, and the impact of environmental change is far-deep. Speciation analysis of elements in sediments is a very important way for understanding land-sea interaction in the estuary and the influence of human activity.In this thesis, based on the complexity of the sources and abundant environmental information for the sediments in the Changjiang estuary and its adjacent area, the modified Tessier sequential extraction procedure is applied to the surface sediments of Changjiang estuary and its adjacent area, to identify the element source and the environmental information. The elements in sediments are partitioned into five fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter, and residual. The eleven major and minor elements in each fraction are analyzed, and the conclusions are drawn as follows:(1) Al, K, Ti and Ba almost all occur in the residual fraction. The temporal and spatial distributions are mainly controlled by sedimentation of terrigenous debris under the hydro-dynamic conditions in the estuary. Their environment mobilities are very weak.(2) In the most sites, Fe,Co,V,Cu,Pb and Sr in sediments mainly occur in the residual fraction, but each element in the non-residual fraction also has a relative high proportion and the average percentages extracted show that Pbï¹¥Srï¹¥Coï¹¥Cuï¹¥Feï¹¥V. The proportion of Mn in the non-residual fraction is higher than other elements, and in most sites it is more than the proportion in the residual fraction. (3) For non-residual fraction, except for Sr mainly in the carbonates fraction, Mn, Fe, Co, V, Cu, Pb are mainly associated with the iron-manganese oxides fraction, followed by the carbonates or organic fraction. The proportions in the exchangeable fraction are very low.(4) In the spatial distribution, along the spreading direction of the Changjiang Diluted Water, except for the proportion of Sr in the carbonates fraction increasing, the proportions of most elements in each fraction are all the highest in the land-sea mixing zone, and lower in both sides. At site C02(or site C03) (where the salinity begins to increase), and site C04 (where the salinity gradient is larger), the concentrations of elements change or behave anomalous. At site C01 near the estuary (roughly located xuliujing), the proportions of Cu in the exchangeable and carbonates fractions, and most elements in the iron-manganese oxides fraction, are relative high. In the vertical spreading direction of the Changjiang Diluted Water, other proportions in each fraction show no change, and fluctuate narrowly in the north area, middle area, and south area. The overall distribution patterns are significantly controlled by the diluted water spreading and the range of the plume, and are closely related to the water salinity, the concentrations of suspended matters, the grain sizes, pH, as well as the contents of organic matters.(5) Compared with the speciation distributions of elements in sediments between two years, the concentrations and proportions of the elements in the carbonates and organic fractions in sediments of most sites are higher in 2006 than in 2003, especially for the carbonates fraction significantly.The concentrations and proportions of the elements in the exchangeable and iron and manganese oxides fractions are decreased in 2006, only the relative enriching in individual sites. Furtherly, compared with the sum of first four fractions (exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter) (that is the effective speciation) in 2003, the average concentrations and percentages of the effective components in sediments of the year of 2006, show no significant differences for Fe, Mn, Co, Pb, a decreasing trend for Cu, and an increasing trend for V. The distribution patterns of the effective components are different between two years. Along the spreading direction of the Changjiang Diluted Water, the position and range of high points all change. The position moves towards the mouth of esturary in 2006, and the range decreases apparenty. In the vertical spreading direction of the Changjiang Diluted Water, the proportion of each element in the effective speciation shows no significant change in all profile of the year of 2003. In 2006, except for the distribution of Pb similar to that in 2003, the concentrations of other elements are high in the north than those in 2003, and behave little change or a decreasing in the south. These characters reflect that, after the first stage in the Three Gorges Project, the spreading range and strength of the Changjiang Diluted Water change towards the south and the north, resulting in the change of speciation distribution patterns of elements in the the south and the north.