Methane emission from Yangtze estuarine wetland, China

Yangtze estuary, lying in the subtropical monsoon region of China, is characterized by a unique environmental setting and endemic wetland plant species (Scirpus mariqueter). Methane (CH₄) emission fluxes were measured at the Yangtze estuarine wetland, Chongming Dongtan (CD), by a static closed chamber technique from May 2004 to April 2005. The results showed that CD is the source of atmospheric CH₄, and emission fluxes had significant diurnal and seasonal variation. The annual average CH₄ emission flux was 2.06 mg m^-2 h^-1 at the CD marsh site and 0.04 mg m^-2 h^-1 at the CD bare tidal flat (nonvegetated). Wetland plant species (S. mariqueter) and temperature were the primary factors controlling the CH4 émission. The results of the light and dark chamber comparison and plant shoot clipping experiment suggest that molecular diffusion and . convective gas flow methods were the two main mechanisms of CH₄ transported via S. mariqueter plants in July. However, molecular diffusion was believed to be the primary transport mechanism from August to October, with leaf resistance as one of the factors regulating CH₄ diffusion. There was significant correlation between CH₄ fluxes and temperature, especially the 10 cm depth ground temperature (R² = 0.7784). Although sediment organic carbon content did not determine CH₄ fluxes, net ecosystem production was significantly correlated with CH₄ fluxes, suggesting that the photosynthates of S. mariqueter effectively provided the substrate for methanogenic bacteria.