The magnitude of the net greenhouse gas (GHG) sink strength of wetlands and mechanisms driving C fluxes remain uncertain, particularly for subtropical and tropical wetlands that are responsible for the majority of wetland CH4 emissions globally. We determined the exchange of CO2 and CH4 fluxes between a subtropical wetland and the atmosphere and investigated how changes in water table (WT), soil temperature (ST), and Gross Primary Productivity (GPP) alter CH4 fluxes. Measurements were made using the eddy covariance technique from June, 2013 to December, 2015.
Results/Conclusions
Wetland was a net sink of CO2 from the atmosphere and source of CH4 to the atmosphere. Increases in temperature, water table depth (WT) and PAR increased GPP during the dry and wet seasons. The contribution of dry season CH4 emissions to annual CH4 budget was substantial (41-to-49%), suggesting that nearly continuous observations of CH4 fluxes may be needed to obtain accurate estimates of the C budget of subtropical wetland. Increases in temperature and GPP enhanced Reco, which decreased with WT during inundation and increased with WT during non-flooding conditions. Fluxes of CH4 increased with temperature and WT, and they increased with GPP only when soils were inundated during both the dry and wet seasons. Emissions of CH4 were further regulated by duration of flooding as they were maximal and sustained after 7 days of preceding flooding. Our results indicate that incorporating the differential influence of climatic and vegetation factors on the responses of CO2 and CH4 fluxes related to soil flooding condition in Earth system models may increase the accuracy in predictions. Warming and seasonal changes in precipitation affecting vegetation as predicted in future climate change scenarios will likely affect the potential for positive feedbacks of subtropical wetland to climate.