The Activity Of Typical Vegetation To The Distribution Of AVS And Heavy Metal About Sediment On Dongtan

In Chongming Dongtan Wetland, the 18 columns about each season were collected in April 2009 to August 2010,and more than 200 samples were cut in the sequence about the 18 columns. To analyze the distribution about temporal and spatial of the AVS and SEM in the sediment samples, its findings show that:(1)Spartina comparison with the Scirpus, Spartina vigorous growth and roots developed, could promote subsidence and deposition of sediment rapidly, so with the accumulation of AVS and SEM, which shows that the content about AVS and SEM is higher in Spartina than in the Scirpus at the same depth.(2)Moisture content, organic carbon content and total sulfur content is the environmental factors which could affects the AVS content. To analyze the correlation about the environmental factors, it shows that it has some correlation between moisture and the AVS content, but moisture content and organic carbon content are not the decisive factor about the AVS content. Moreover it has a significant correlation between the total sulfur content and the AVS content, and the correlation coefficient is above 0.5, and the higher is up 0.739. It shows that the total sulfur is the controlling factors about the AVS.(3)Tides affect the AVS content, and affect the ratio of SEM/AVS at the same time. The ocean brings a lot of sulfate at the high tide, adds plenty of SO42-, provides a sufficient basis, so the AVS is higher and the ratio of SEM/AVS is lower. Heavy metals on benthic toxic effect dose not exist.Sediment exposed to air at low tide, the S2- is oxidized and the content of AVS is reduced, but the ratio of SEM/AVS is higher, so heavy metals on benthic toxic effect exist.(4)The content of Zn is the highest, and the order of high to low about heavy metals is SEMzn>SEMCu>SEMNi>SEMCr>SEMpb.EM contribution of Zn on the rate of nearly 50%, so SEM distribution in the vertical mode is mainly controlled by the Zn element. The ratio of bioavailability about Cu is the largest, so Cu may be easier to produce toxic effects on the benthos. Spartina comparison with the Scirpus, the ratio of bioavailability about Cr and Cu and Ni is higher in Spartina, and the ratio of bioavailability about Pb and Zn is higher in Scirpus.(5)The content distribution of SEM and the total heavy metals is higher at the surface of the column and is lower at the bottom of the column, which reflects the history of heavy metal at the Yangtze River Estuary in recent years. Compared with Chinese soil environmental quality standards, Cr elements is less than one standard and the others are higher than one standard bur less than two standards, that reflects the history of heavy metal at the Yangtze River Estuary in recent years all the same.(6)Through the analysis of SEM/AVS andΣSEM-AVS, the results show that SEM/AVS under the cover Spartina sediments is lower than the Scirpus. Because under the cover of Spartina heavy metal elements are adequate AVS are fixed, no toxic effect on the benthos. Tides have a profound impact on the SEM/AVS, which related to the heavy metals bioavailability. When the big tide, SEM/AVS small and less than 1, so the heavy metals will not produce toxic effects on the benthos; When neap tide, because the sediments exposed to air, most of the sulfide is oxidized,the fixed heavy metals are released, making the SEM/AVS ratio increases, so easily this time of heavy metals have toxic effects on the benthos.In some layers, although the ratios of SEM/AVS is greater than 1, taking into account the margin of SEM-AVS is too small, so heavy metals will not produce toxic effects on the benthos.