Temporal And Spatial Distribution Of Soil Profile CO₂/CH₄ And Its Influencing Factors

Greenhouse gas emissions and global climate change are closely related to the wetland ecosystem carbon cycle. The production and release of soil profile CO2 and CH4 is an essential components of ecosystem carbon balance, thus the research of its concentration distribution and emission characteristics is of great importance for better understanding and predicting the global carbon cycle. In this article, three kinds of wetland ecosystems in the subtropical monsoon climate zone of China (urban wetland-XX, natural wetland-XZ and paddy field-JS) were selected as the objects to examine the within site spatial and seasonal variability, and differences among sites of subsurface CO2 and CH4 concentrations as effected by hydrological conditions and wetland types. The correlation models relating soil CO2 and CH4 concentration to soil temperature and volumetric soil water content were build. The CO2 and CH4 emission fluxes and its influencing factors were analysized. The main findings are as follows:1. Temporal and spatial differences of soil profile CO2/CH4 concentration were affected by both hydrological conditions and wetland types. Paddy field, natural wetland and urban wetland (non-waterlogged site) showed the similar seasonal variation pattern, the CO2 concentration in the summer and autumn significantly higher than those in the spring and winter. Vertically, the soil profile CO2 concentration increased with the increasing depth. The CH4 concentration of paddy field also showed the evident seasonal variation pattern, and the soil profile CH4 concentration decreased with increasing depth.2. Soil profile CO2 and CH4 concentration were significantly positively correlated with soil temperature and soil volumetric water content. The correlation coefficients of soil profile CO2 concentration and soil temperature or soil volumetric water content were 0.251-0.813 and 0.266-0.251 respectively. And the correlation coefficients of soil profile CH4 concentration and soil temperature or soil volumetric water content were 0.219-0.437 and 0.311-0.500 respectively.Polynomial equations y=a+bT+cW+dT+eW2 were used to describe the dependency of soil profile CO2/CH4 concentration on soil temperature (7) and volumetric soil water content (W). However, it did not significantly improve modeling fitting compared with those fitted using univariate for each site.3. Regardless of hydrological conditions, three kinds of wetland ecosystems acted as CO2 emissions (carbon source). However, the CH4 fluxes were dependent on hydrological conditions and wetland types, CH4 fluxes for paddy field, natural wetland and urban wetland (non-waterlogged site) were negative, indicating CH4 absorption (carbon sink), urban wetland (seasonal waterlogged site) as CH4 emissions (carbon source). CO2 or CH4 fluxes were significantly positively correlated with soil temperature, soil volumetric water content and CO2/CH4 concentration under different soil depth (10-50cm) (p<0.05).4. As to paddy field and urban wetland (seasonal waterlogged site), soil profile CH4 and CO2 concentration showed a significant positive correlation (p<0.01), the correlation coefficient was 0.271 and 0.195. Soil CH4 and CO2 fluxes were significantly positively correlated for all soils, the correlation coefficient ranged between 0.384 and 0.749.