| Pollutants would eventually sink in sediments in the offshore area. It had showed some degrees of restricted factors of social and economical development. This was the first investigation in Zhejiang Province with magnitude and high dense about the sediments in the offshore area of eastern Zhejiang Province. This investigation increased our knowledge of concentrations, distribution, controlling factors and sources of these chemical elements. According to the investigation results, the government of Zhejiang Province could establish the layout for the economic development of coastal regions and implement the macro adjustment. In the present paper, surface sediment samples collected from 140 stations and sediment cores collected from 22 stations in the offshore area of eastern Zhejiang Province, were analyzed for 21 kinds of components (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn, C, N,P, S, SiO2, Fe2O3, Al2O3, MgO, CaO, Na2O, K2O, pH, OrgC). In especially, we discussed eight trace elements distribution (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) characteristics of surface sediments and vertical cores and vertical coastline sediments. We gained enrichment state of trace elements and the effect of human activities to sediments quality and got the environmental background values of eight trace elements by statistical and normalized ways and 210Pb data. On the basis of the environmental background values, we assessed the sediments quality by index of geoaccumulation, enrichment factors, contamination degree and divided the sediment quality into three levels in the study area. According to the correlation between trace elements and sediment particle size, we concluded the main sediment diameters range of enriched trace elements in the study area. The main results concluded were as follows. The contents of trace elements (except for Cd) in this study area were similar with those of average sediments of Changjiang River, but were generally high in As, Cr, Cu, Hg, Ni, Pb and Zn, compared to those of average coastal sediments of China and Huanhe River. The levels of As, Cr, Cu, Ni were higher than those of rocks and drainage sediments of Zhejiang Province. Aluminum oxide level was similar to other areas. The means of trace elements (except for Cd) were less than the Sediment Quality Standard. The levels of trace elements, Al2O3, Fe2O3, MgO, K2O, OrgC in sediments of Yueqing Bay and the south of Jiaojiang Estuary and the inner of Sanmen Bay were higher than other areas. However, the distribution of SiO2 and CaO showed opposite trends. The main functions of them were dilution. The contents of C, N, P, S were higher in Jiaojiang estuary. The correlation analysis between trace elements and other components in surface sediments showed that the relativities between trace elements and clay mineral and granule sediments were strong. The relativity coefficients between trace elements and SiO2 and pH were minus. The normalized trace elements showed that the effects of human activities to sediments were light. Mercury suffered from the human activities seriously. Zinc suffered from the human activities gently. The relativity coefficients between sediment particle diameters and trace elements showed that when particle diameters were more than 6.5φ, the relativity coefficients were higher and when particle diameters were less than 6φ, the relativity coefficients were minus and when particle diameters were more than 9.5φ, the relativity coefficients showed gradually decrease. Hydrodynamism and land form were the first factors controlling the trace elements distribution. Organic carbon together with clayey mineral and pH and sediment particle diameters was the second factors. Among the second factors, the contents of SiO2, Fe2O3, Al2O3, MgO, K2O, OrgC were common controlling factors to As, Cr, Cu, Hg, Ni, Pb, Zn. The contents of N and clay also affected the distribution of As, Zn, Cr, Cu, Ni, Pb. The contents of clay also affected the distribution of Zn, Cr, Cu, Ni, Pb. The contents of P also affected the distribution of Cr, Cu, Ni, Pb, Zn. The contents of silt affected the distribution of Cu, Ni, Pb, too.The study area could be divided into two groups by model Q Cluster analysis which were based on eight trace elements: enriched region and unenriched region. The enriched region included Sanmen Bay and the south of Jiaojiang estuary and Yueqing Bay. The unenriched region included Xiangshan and Aiwan Bay and Xuanmen Bay. The main characteristics of sediments in cores were silt including peat layers. The existing of peat layers in 180 cm of sediment cores or so showed that changes took place in sediment surroundings in such depth. The relativities between depth and trace elements showed that the distribution were different from different sediment cores. It showed enrichment on the upper for As, Cd, Cu, Hg, Ni, Pb in JHSE21 core, for As, Cd, Cu, Hg, Zn in JHSE41 core. Sediment cores could be divided into upside and downside on the scale of 1800 year, based on the 210Pb data and the distributions in cores. The contents of trace elements in upside were more than those in downside, which could demonstrate the change of sediments source. The normalized trace elements in cores showed that in different area the effects of human activities to trace elements were different. Copper together Hg and Pb suffered from anthropogenic input in Xiangshan offshore area, and in Taizhou Bay the main elements were As, Cd, Cu, Hg, Zn. The distribution of trace elements in sediments of vertical coastal profiles showed that the change trends between surface layer levels and mean were unanimous, but the degree and rhythm were different. And the contents of surface layers were more than the average. The difference also existed. For the JHSE21 vertical coastal profile, the patterns were that the contents of trace elements in the offshore area were higher and when the distance from coastline increased, the contents decreased. It made out the effects of human activities. For the JHSE31 vertical coastal profile, the patterns were complex and eight trace elements had different distribution trends. The contents of trace elements of surface layer and... |
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