Study On Emission Fluxes Of CO₂and CH₄and Their Vertical Distribution Characterizations Of Soil From Wetlands In Southeast China

Wetlands play an important role in carbon storage, and the carbon balance of wetlands is sensitive to climate changes. However, current studies focus on North wetlands, and there is a lack of vertical distribution data of carbon dioxide (CO2) and methane (CH4) from wetlands. Here field measurements were conducted from three typical wetlands (urban wetland, lake wetland and paddy field) in Zhejiang province in Southeast China. CO2and CH4emission flux measurements were conducted using a static opaque chamber-gas chromatography technique, and the soil gas samples were measured with gas chromatography. Simultaneously, the temperature, pH and redox potential (Eh) of soil were measured in situ, and the soil samples were collected and brought back to lab for measurements of dissolved organic carbon (DOC), soil organic carbon (SOC) and total nitrogen (TN). The relationship between them was also studied. Arc-GIS, Origin8.0, SPSS16.0, Excel2007, PAST image and data processing software were applied, and correlation analysis, cluster analysis and other mathematical methods were utilized to explanation. The results showed that:1) Three typical wetlands acted as sources of CO2during both autumn and winter, while the study sites were CH4sources during autumn and acted as small CH4sinks during winter. Additionally, very high CO2and CH4efflux were observed from paddy field during autumn.2) There were obvious vertical distribution characterizations/seasonal patterns of soil temperature, pH, Eh, SOC, DOC and TN.①Soil temperature became close with depth during autumn, while increased with depth during winter.②Wet deposition resulted in the acid soil during autumn.③The soil Eh in seasonally waterlogged (SW) regions was higher than that in not-waterlogged (NW) regions during autumn.④The SOC and TN of surface soil were higher than that of other layers. The DOC and TN of0-30cm from paddy field were higher than that of other sites. Additionally, the metabolism of fine roots resulted in a peak DOC/SOC at depths of20-30cm.3) There were obvious vertical distribution characterizations of element content. The clustering procedure generated three groups of sampling sites in a very convincing way. The NW regions from urban wetland (XXA) and lake wetland (XZA) could be grouped into Cluster1, the SW regions from urban wetland (XXB) and lake wetland (XZB) could be grouped into Cluster2, and the SW regions from paddy field (JSB) could be grouped into Cluster3. Cluster1, Cluster2and Cluster3correspond to a relatively low, moderate and high soil greenhouse gas concentration, respectively.4) Cluster1, Cluster2and Cluster3correspond to a relatively low, moderate and high soil CO2concentration, respectively. Soil CO2concentration increased with depth in Cluster1. Additionally, The peak soil CO2concentration occurred in depths of20～30cm in Cluster2and Cluster3. For Cluster1, soil pH and Eh were the major controlling factor for soil CO2concentrations during autumn, and soil temperature and pH became the major controlling factor during winter.5) Cluster1, Cluster2and Cluster3correspond to a relatively low, high and high soil CH4concentration, respectively. Waterlogged condition resulted in high soil CH4concentration from wetlands. Distinct high concentrations of soil CH4occurred at depths of20-40cm in autumn, while occurred at depths of30-50cm in winter in Cluster2. Additionally, soil CH4concentration increased with depth in Cluster3. A relatively low soil CH4concentration was a synthesize result of low temperature and high pH during winter.