Methane flux and production from sediments of a mangrove wetland on Hainan Island, China

Methane fluxes from sediments in different zones of a Bruguiera sexangula mangrove wetland were determined by closed static chamber techniques during one whole year period, at Changning River estuary, northeast of Hainan Island, China. Methane productions were also measured by anaerobically incubating sediment samples. Impacts of salinity, sulphate and temperature on methane production rates were studied in vitro. Great differences of annual methane fluxes were observed in three zones, with the values of 0.39, 0.20 and 0.12 g m^-2 in the outer zone, middle zone and inner zone, respectively, in part due to the differences of sediment water contents and crab bioturbation. The highest fluxes in each zone occurred in autumn and the lowest in winter. Large diurnal fluctuations in fluxes were caused by the changes of tidal conditions rather than the changes of air or sediment temperatures. The temporal and spatial patterns of methane production differed somewhat from those of methane flux. There was great seasonality for methane production and the highest productions were found in autumn and the lowest in spring. Different horizontal and vertical patterns occurred in different seasons and different zones, suggesting the complexity of factors controlling methane production. The in vitro control experiments indicated that salinity and sulphate had negative effects whereas temperature (20-50°C) had positive effects on methane production rates. However, there were different sensitivities for the different levels of the three factors.