| Distribution of heavy metals and biogenic elements in the sediments from the East China Sea and Yellow Sea have been studied.80 surface sediment samples was collected from the East China Sea and Yellow Sea in May 2009.3 core samples was collected in April-May 2010 from the Yangtze River estuary. Hotizontal and vertical distribution of heavy metals and biogenic material (carbon, nitrogen, P, Si) has been analysed. Evaluation of potential ecological risk of heavy metals and toxicity evaluation of biogenic elements in the Yangtze River Estuary and the Yellow Sea were conducted for a comprehensive understanding of the marine environment in the area. The results are as follows:(1) The range of the content of Cu, Mn, Pb, Zn, Cr, Fe, Hg, Cd in the surface sediments of the Yellow Sea was 6.13～38.25 mg/kg,106.8～2353.8 mg/kg,8.13～33.38 mg/kg,23.2～114.0 mg/kg,18.1～56.3 mg/kg,1.29～5.48%,0.005～0.052 mg/kg and 0.056～0.376 mg/ kg, respectively. Their average values were 18.84 mg/kg,626.2 mg/kg,17.64 mg/kg,56.7 mg /kg,32.5 mg/kg,2.73%,0.019 mg/kg and 0.132 mg/kg.The contents of Cu, Pb, Zn, Cr, Fe, Hg in the surface sediments of the Yellow Sea were higher in the mid of South Yellow Sea and west of North Yellow Sea but lower at the Haizhou bay and north of the North Yellow Sea. The potential ecological risk evaluation indicated that the surface sediment in the major sites are in the slight ecological risk condition, but that of some other sites are in moderate condition. The potential ecological risk of these heavy metal was in the order of Cd>Hg>Cu>Pb>Cr>Zn, with the highest potential ecological risk of Cd in the Yellow Sea. The lower sediment environmental quality was distributed in the the mid of South Yellow Sea, according to results of cluster analysis.(2) The range of the contents of Cu, Mn, Pb, Zn, Cr, Fe, Hg, Cd in the surface sediments of the Yangtze river estuary was 2.00～37.75mg/kg,256.25～776.13 mg/kg,5.75～29.88 mg/kg, 19.5～100.25 mg/kg,14.25～51.5 mg/kg,1.1-7.42%,0.003～0.079 mg/kg and 0.016～0.347 mg/kg, with their average contents being 17.34 mg/kg,424.73 mg/kg,16.25 mg/kg,55.53 mg/kg,31.65 mg/kg,2.89%,0.016 mg/kg and 0.106 mg/kg, respectively.The heavy metals ofCu,Mn,Pb,Zn,Cr,Fe, in the surface sediments of the Yangtze river estuary, distributed in a declined trend from the west to the east within the estuary and its adjcent areas, and increased from the middle area to the Cheju Island. In general, the content of heavy metals were higher in the coastal waters of Xiangshan Bay and Zhoushan Islands than that in the northern area. The Hg content was higher in southern Yangtze river estuary and declined all the way from the west to the east. The Cd content was higher in southern Yangtze river estuary and lower in the middle area. The potential ecological risk evaluationindicated that surface sediments in the major sites within the Yangtze river estuary and its adjacent areas were in the slight ecological risk condition, whereas those of the other sites were in moderate condition. The potential ecological risk of these heavy metal was in the order of Cd>Hg>Cu>Pb>Cr>Zn. Cd and Hg were with the highest potential ecological risk in the areas. The lower sediment environmental quality was distributed Xiangshan Bay, the offshore waters of the Yangtze River Estuary and the southwest of Cheju Island, according to results of cluster analysis.(3) The analysis of the heavy metals in columnar samples from za3, dcll, gd26 showed that za3 had the highest average content of each heavy metals. Combining with za210Pb radioisotope dating results, it indicated that there was no large fluctuations of heavy metals during the last three decades in Za3. However, except that of the Hg, an obvious increase trend was found in all other heavy metals. In Dc11 station where close to Yangtze River estuary, the content of every heavy metal decreased from the bottom to the surface, with the biggest variation of Cu, accounting for 90% of the average. The probably reason was the reduced runoff of Yangtze River since 2000. gd26 station had a relatively stable content of heavy metals at depth below 7cm, whereas the values soared at the top 7cm depth, indicating a deterioration of environmental quality in this region.(4) Compared to other waters, biogenic elements content in surface sediments of the Yellow Sea were moderate. The ranges of concentration variation of organic carbon (TOC), total organic nitrogen(TON), total phosphorus(TP) and biogenic silica(BSi) were 0.18%-1.36%, 0.03%-0.29%,0.029%-0.506% and 0.706%-1.588%, with the average content 0.68%,0.13%, 0.046% and 1.109%, respectively. The values of TOC/TON ratio indicated that the origination of the main source of organic carbon was aquatic organic carbon in the southern region of South Yellow Sea, while it was mixed source of the marine aquatic phytoplankton and land-based source in the north of N36°within the Yellow Sea region. The content of biogenic elements in the surface sediments of Yangtze River Estuary were moderate, compared to other estuarine waters in the world. The variation range of TOC, TON, TP, Bsi were 0.16%-1.31%,0.03%-0.23%, 0.035%-0.076% and 0.62%～1.26%, with the average values of 0.65%,0.12%,0.050% and 0.99%, respectively. The main source of organic carbon was aquatic organic carbon in the north of Yangtze River estuary and adjacent waters of the Yellow Sea.(5) The contents of TOC, TON, TP in za3 increased slow from the bottom to the surface, while the BSi had no obvious trend. On dcll station, the content of TOC decreased from the bottom to the surface, while those of TON and TP increased gradually. On gd26 station, similar vertical distribution patterns were found in TOC and TON. The content of TP changed slightly from the bottom to the 2cm below the surface, but increased rapidly in the surface. It was probably due to the high diffusion of nutrients from seawater to the sediment samples. BSi changed intensively in the vertical direction. The results showed that za3 station had the highest average contents of TOC, TON, TP, which was in accordance with the distribution of heavy metals, supposing that za3 station was impacted more by the terrestrial input and accepted large number of land-based pollutants. |
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