| In order to reveal the influence of salt marsh environment on the organic carbon cycle of surface sediments in wetland,this paper selects the high tide beach,middle tide beach and bare flat of Chongming East Carbon Salt Marsh as the research area.Total organic carbon(TOC),Readily oxidizable carbon(ROC),Dissolved organic carbon(DOC),Hydrolyzes organic carbon(HOC),Recalcitrant carbon(RC)of 0~30cm depth sediment samples from Spartina alterniflora belt,Phragmites australis belt,Scirpus trigueter belt,Scirpus mariqueter belt and bare flat were compared.Mainly compared the spatial distribution characteristics of the content and the organic carbon structure.And using C/N ratio and isotope tracer method to explore the source of organic carbon in the surface sediments of salt marshes.The results show:(1)The TOC content and Cd value of all samples showed a significant trend of decrease from northwest to southeast,ranging from 0.51~39.2g C/kg and0.0030~0.0167 g C/cm~3,respectively.TOC and Cd values of sediments in dongtan salt marsh were 7.85±3.43 g C/kg and 0.0087±0.0024 g C/cm~3,respectively.The contribution of vegetation to organic carbon in sediments was diluted by faster sediment deposition and lower organic carbon content,which were lower than those in other areas.The overall characteristics of the vertical distribution of the TOC content in the sediments from 0 to 30 cm showed that the TOC content fluctuated and decreased with the increase of depth.Under the influence of root system input and fine sediment,there would be obvious peak of TOC at some depths.Sedimentation,plant burial and mineralization also affect the organic carbon composition of salt marsh.The soluble carbon pool accounted for only 0.61±0.38%(between 0.24~2.27%)of TOC,the oxidizable carbon pool was 15.6±5.64%(between 1.77~43.6%),and the acid-hydrolyzed carbon pool was the largest.The average value(57.2±21.7%)was more than half of TOC,accounting for 0.12~99.8%.The size of activated carbon pools in sediments in the study area is controlled by total organic carbon content.(2)The C/N ratio of surface sediments in the salt flats of Chongming Dongtan was greater than 9,indicating that the organic carbon in sediments may be the result of mixed input of terrestrial organic carbon and sea-source organic carbon.The three-terminal mixed model indicates that the organic carbon in the sediments of the study area was mainly derived from suspended particulate matter(32.33±8.23%)and terrestrial vegetation in the basin(54.20±13.41%),and the contribution of benthic microalgae is small.(13.46±6.50%).The source of organic carbon in salt marshes and its contribution rate are represented by two modes in spatial distribution.The first model is located in the northern part of the salt marsh.The TOC content of the sediment was high.The organic carbon was mainly derived from suspended particulate matter and vegetation contribution(38.31±7.78% and 41.46±5.13%,respectively),and the contribution of benthic microalgae is the lowest(20.21±4.18%).The model was located in the south of the salt marsh,and the sediment TOC content was low.The sediment organic carbon was mainly derived from the salt marsh vegetation(59.10±12.34%),followed by the suspended particulate matter and benthic microalgae contribution(30.04±7.42% and 10.86±5.25% respectively).In general,from the north to the south of the salt marsh,the contribution rate of vegetation increased,and the contribution rate of suspended particulate matter and the contribution rate of benthic microalgae showed a downward trend. |
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