The Temporal and Spatial Distribution Characteristics and Pollution Assessment of Carbon, Nitrogen and Heavy Metals in Wetland Sediments of Hangzhou City
|School||Hangzhou Normal University|
|Keywords||Xixi wetland Hemu wetland distribution characteristics of carbon nitrogen depth bulk density distribution characteristics of heavy metals pollutionassessment ecological risk assessmen|
In this study, the research subjects were Xixi wetland and Hemu wetland of Hangzhou city, surface sediment samples and sediment cores were collected in two wetlands, for studying the level distribution、seasonal distribution and vertical distribution characteristics of organic carbon、total nitrogen and heavy metals in sediments. And then the pollution assessment and ecological risk assessment of carbon、nitrogen and heavy metals of sediments in the Xixi wetland and Harmony wetland was studyed. The results showed that:(1) Overall level of total organic carbon (TOC) and total nitrogen (TN) contents in Xixi wetland surface sediments were high. Total organic carbon (TOC) ranged from10.33g/kg to45.06g/kg and total nitrogen (TN) content ranged from1.6g/kg to6.7g/kg. From the point of seasonal distribution, TOC average content of surface sediment in Xixi wetland in April was highest of29.84g/kg, while the average content of TN in surface sediments was relatively higher in November and was up to4.9g/kg. Compared with the Xixi wetland, the overall content of total organic carbon (TOC) and total nitrogen (TN) of surface sediment in Hemu wetland were low, and the range of total organic carbon (TOC) and total nitrogen (TN) concentration were10.02-27.83g/kg and0.41-4.48g/kg, respectively. Based on the seasonal distribution, the total organic carbon (TOC) and total nitrogen (TN) content of surface sediment in Hemuwetland were the highest in January.(2) On the vertical distribution characteristics of total organic carbon and total nitrogen content of the sediments in Xixi wetland Ⅰ,Ⅱ, Ⅲ Phase and Hemu wetland, organic carbon content, organic carbon density, total nitrogen content and total nitrogen density of the four cores sampling point were higher in surface and had a trend of gradually exponential decline with depth increasing. Further correlation analysis showed that the total organic carbon and total nitrogen content of sediment in Xixi wetland Ⅰ,Ⅱ, Ⅲ Phase and Hemu wetland were a significant linear relationship, and they had significant negatively relationship both with soil depth, bulk density.(3)The surface sediments ON%index in the Xixi wetland and three sampling points of Hemu wetland exceeded the level of "pollution/Ⅳ". Organic index were mostly multiples lower than the ON%index in different sampling points of two wetlands, the organic index of the sampling of point Boan in Xixi wetland was highest of1.04], which exceeded twice to pollution standards; organic highest index of the sampling point No.1in Hemu wetland was highest of0.262, it fited the level of less clear/Ⅲ. Compared with the Xixi wetland, the overall level of ON%index and organic Index, toxicity levels of TOC%and TN of surface sediments in Hemu wetlands were lower.(4) In terms of the point of the spatial distribution, the Zn content compared to Cu, Cr, Pb, Ni content in Xixi wetland sediments was the primacy, Zn content range was72.65-159.64mg/kg; for seasonal distribution characteristics, in November, Cu, Zn content of sediments in Xixi wetland reached a minimum, Cr, Ni content were up to the maximum in September, but Pb content was differences in the annual fluctuations trend of each sampling point. For the spatial distribution, sediments heavy metals with high Zn, Ni, Cu, Cr, content was the main feature of Hemu wetland; for seasonal distribution characteristics, the content of sediments heavy metal with high Cu, Zn, Cr. Ni content in July and January was the main feature of Hemu wetland.(5) Vertical distribution characteristics of heavy metals in sediment cores form Xixi wetland I, II, III phase and Hemu wetland showed that the heavy metal contents of the four cores sampling point were jagged multimodal distribution characteristics with changing depth and presented sawtooth trend differences, and there were overall downward trend from deep to shallow. The average concentration of heavy metals in the order was Zn> Cu> Pb> Ni> Cr. Compared with the environmental quality standards, the heavy metal content of the sampling points in the four cores was between background value of Hangzhou city soil and secondary standards of soil quality. Then compared with Xixi wetland, overall the heavy metal content of the Hemu wetlands was higher.(6) Single pollution index evaluation showed that Cu, Zn, Ni pollution were relatively consistent with the Xixi wetland and Hemu wetland sediments, but the Cr pollution level of sediments in Hemu wetland was much higher than Xixi wetland. Hakanson potential ecological risk index (RI) evaluation showed that, the overall ecological risk in Xixi wetland was minor, the potential ecological risk index of the annual heavy metals in Wuyi Bridge was highest. In addition, Xixi wetland had a contamination characteristic with Ni, Cu-based multi-kinds of heavy metals. The RI of sampling sites in Hemu wetland were classified as minor level of risk, and the potential ecological risk factor were Cu and Cr.