Carbon And Nitrogen Sink Capability And The Ecological And Environmental Effect In Yangtze Estuarine Wetland

In the past few years, the global warming trend has been widely concerned. The cycling of carbon and nitrogen in the ecosystems has become a research hot spot. Natural wetland occupies an important position in global change due to the large area and the role as carbon sink and denitrification. As one of the world’s most important estuary, the Yangtze River Estuary acts a significant part in the control of carbon and nitrogen cycling in this region. It has become a widely acknowledged research direction to study the carbon sink function, denitrification, and the influence of vegetation on denitrification of Yangtze River Estuary.In this study, we carried out the following works:1.Collected sediment samples in Chongming Dongtan of Yangtze River Estuary, and analyzed the variation of soil organic carbon (SOC) content in different vegetation types with depth and time and compared with the results of previous tudies of our team; 2. Collected soil samples in the farmland area of Chongming Island, and analyzed the variation of SOC content under different cropping system; 3. Feldspar powder was sprinkled on the sediment and pipes were buried in Scirpus mariqueter growth area in Chongming Dongtan, to study the sedimentation rate and the effect of vegetation on SOC content in different depth, and analyze the source of SOC in the region using 13C isotope; 4. Selected typical vegetation regions in Yangtze River Estuary wetland and collected sediment samples to study the denitrification, analyzed the spatio-temportal difference of sediment denitrification rate in different vegetation types and the effects of environmental factors, and estimated the ability of intertidal sediments to remove nitrogen from the overlying water and the water source in Yangtze River Estuary. The major conclusions are as the following:(1) Vegetation area along the Yangtze River Estuary wetland intertidal zone had a certain relationship with the year, and it was significantly correlated with annual sediment discharge. Average sedimentation rate in this region was 11.6 cm/yr, measured by the feldspar powder labeling method. The annual carbon storage in the vegetation area of Chongming Dongtan reached 5.70×104t/yr, and the buried carbon flux was 1.09 kgC/m2/yr, which represented the significant carbon sink effect.(2) In the eastern of Chongming Island, the SOC content in the soil and sediment decreased from the central region to the surrounding areas, just like a saddle trend. It was especially high in the central farmland region and lowest in mudflat of Chongming Dongtan. In addition, the SOC content in paddy cultivation area was significantly higher than in dry vegetable area. In the intertidal zone, SOC content in the sediment gradually decreased with the change of vegetation types(Phragmites/ Spartina alterniflora-Scirpusmariqueter/ Spartina alterniflora-mudflat), which was lowest in the mudflat.(3) In recent years, the annual average SOC content increased with the year that’s in the Scirpus mariqueter community sediment and mudflat surface sediment. There was obvious difference of SOC content in the surface sediment between various vegetation communities, which was lowest in the mudflat, and highest in Spartina alterniflora area. The SOC contents of all the vegetation communities decreased with the depth, the maximum SOC often appears in the surface 0-5 cm sediments. From the seasonal variation, the SOC contents of all the vegetation communities was lower in summer, and higher in the autumn, winter and spring.(4) The average SOC content in Scirpusmariqueter sediment was significantly higher in 2011 than in 2004, but the seasonal variations were basically identical. SOC content fluctuated from 0 cm to 60 cm in the depth, but it showed a trend of decreasing from the top to the bottom on the whole. The SOC content in the sediment that collected every month in Chongming Dongtan varied greatly in Scirpus mariqueter growing season.(5) The results of pipe burying experiment well illustrated the influence of Scirpus mariqueter on SOC. It was found through isotope tracer method that the source of SOC in sediment of Chongming Dongtan was the particulate matter carried by river and the local vegetation growth. Exogenous particles sedimentation was the main source of the sediment carbon library in Yangtze River Estuary wetland. The input rate of SOC from Scirpus mariqueter as endogenous contribution also occupied a certain proportion. It was 0.65 mg/g and 2.06 mg/g in the flood season and dry season, respectively, which accounted for 7.35% and 31.20% of the SOC library approximately.(6) The denitrification rate in the surface sediment (0-10 cm) in Yangtze River Estuary wetland was 0.43-415.8 μmol·m-2·h-1, with an average of 35.5μmol·m-2·h-1. It was in the middle level when compared with most estuaries around the world. The average denitrification rates were 16.2 μmol·m-2·h-1 and 45.2 μmol·m-2·h-1 in mudflat sediment and vegetation area sediment, respectively. The annual total denitrification in Qingcaosha reservoir zone reached 2.00×108 g N, which effectively removed the nitrogen input from atmospheric deposition. It’s of great significance for controlling of the nitrogen accumulation in water and eutrophication in the reservoir.(7) Denitrification rate in Scirpus mariqueter had significantly difference with them in Phragmites and mudflat (p<0.01), but there was no significant difference between in Phragmites and mudflat sediment (p>0.05). In the Yangtze River Estuary wetland, the denitrification rates in sediment didn’t show consistent time-varying pattern for all sites, although significant seasonal difference was found in some of them (p<0.05). The denitrification rate in the surface sedimentwas generally higher than the deeper. The denitrification rate in the sediment was significantly influenced by sampling sites, depth and month, but it had no correlation with single physicochemical properties of sediment, temperature and other environmental factors.(8) In this study, we demonstrated that intertidal zone of the Yangtze River estuary wetland has obvious ecological environment effect such as carbon sinks and removing the nitrogen. Under the background of relative sea level rise and decline in riverine sediment supply, it suggested that we should foster weland protection, reduce the intensity of land reclamation, and establish a wetland system monitoring system and the basic data sharing mechanism. On the basis of strengthening scientific research, wetland should be included into China’s carbon emissions trading list as soon as possible. At the same time, once conditions get mature, nitrogen emissions trading system should also be introduced into the apply of total amount control of pollutant discharge.