Study Of Greenhouse Gases Emissions In Different Succession Stages In Sanjiang Plain Wetland

The wetland is a huge organic carbon pool and also an important emission source of greenhouse gas CH4. Sanjiang Plain is the largest distribution area of fresh water marsh wetland in China. Due to global climate change and multiple artificial interference, there were great changes in the hydrological conditions and vegetation Succession in the wetland. Therefore, this paper mainly studied the characteristics of greenhouse gases emissions and analyzed the carbon sink function and the change of global warming potential in different successional stages in Sanjiang Plain wetlands.With the changes of microtopography and moisture conditions, vegetation succession occurred from typical meadow and swamp meadow in the edge of the ring wetland to swamp communities in the center wetland. Microclimate climate was changed dynamically in different successional stages. With succession proceeding, temperature decreased and humidity increased gradually. The light intensity had a changing trend of first decrease and then increase and further decrease. There were significant difference in the changing trends and intensities for the different levels of microclimate climates.With succession proceeding, TER was reduced significantly. The seasonal variations of TER in different successional stages show a single peak pattern, with the maximum monthly averaged values of1112.61mg-m"2-h-1. TER has obvious interannual changes due to the impact of environmental factors such as temperature and precipitation. In the growing season, maximum cumulative emissions was31.99t-ha-1. The diurnal variation of both TER and temperature showed a single peak pattern. Distribution characteristics and seasonal trends of TER was consistent with that of soil respiration, with a slight difference in diurnal variation. The average concentration of CO2in the soil was2092ppm. In different successional stages, soil CO2concentration was gradually increased with the increasing soil layer. There was a significant exponential relationship between the TER and temperature and logarithmic negative relationship between the TER and water depth.With succession proceeding, CH4flux showed obvious seasonal and interannual variation. The maximum monthly averaged values of CH4flux was72.00mg-m-2·h-1. In growing season, maximum cumulative emissions was2296.11kg·ha-1. There were significant differences in diurnal variation of CH4flux of the wetlands in different succession stages; the impact factors were more complex. Distribution characteristics and seasonal trends of soil CH4flux were consistent with that of the ecosystem CH4flux, but the significance was decreased. The CH4flux of soil was less than CH4flux of, it show that plant has strong shuttle effect for CH4. The average concentration of CH4in the soil was217.95ppm. Soil CH4concentration of different successional stages gradually increased with the increasing soil layer. There was a significant exponential relationship between the CH4flux and temperature and a logarithmic positive correlation between the CH4flux and water depth.Sanjiang Plain wetland was a weak emission source for N2O and there was no significant difference in N2O emission between different successional stages. The maximum emission often occurred at the first two successional stages, with the maximum monthly averaged value of0.145mg·m-2·h-1. In growing season, maximum cumulative emission of N2O was3.90kg·ha-1. The N2O flux was lower in the center of the ring wetlands, or even negative emission, showing a weak absorption. The seasonal, interannual and diurnal variability of N2O fluxes was not significant. Soil N2O fluxes were slightly less than the ecosystem N2O fluxes, with a consistent variation trend. The average concentration of N2O fluxes in the soil was327.86ppb. Ecosystem N2O emission flux was positive and negative linear correlation with temperature and water depth, respectively, but with a low correlation.NEE of Sanjiang Plain wetland ranged from-17.47to-4.78t-ha-1in different succession stages, showing the net uptake of CO2. In the whole successional stages, the wetland showed a net fixed carbon, with the amount of net carbon exchange of-0.87～-4.51t-ha-1, and the carbon sink function was firstly decreased and then increased with the sucession, showing a similar change with that of NEE. From20～500a time scale, GWP in Sanjiang Plain wetland was increased gradually with succession proceeding. GWP in the different successional stages mainly depends on the CH4emissions and the net fixed CO2. With the extension of the time scale, the warming potential of the three greenhouse gases began to decline, of which the warming potential of CH4showed the most obvious decline. As CH4greenhouse effect is weakened gradually, global warming potential was also decreased gradually.