Methane and Carbon Dioxide Fluxes from a European Alpine Fen Over the Snow-Free Period

Wetlands play an important role in the global carbon cycle and are sources and sinks for the greenhouse gases methane (CH4) and carbon dioxide (CO2). We provide an in situ study on variability of daytime CH4 emissions and net ecosystem CO2 exchange (NEE) from a permanently submerged, Carex rostrata dominated Swiss alpine fen over the snow-free period (June-October). Flux chamber measurements were combined with analyses of above-ground biomass and physico-chemical pore water properties. The fen was a net daytime CH4 source throughout the snow-free period, and emissions varied significantly between the sampling dates, ranging from 3.1 +/- 0.9 mg CH4 m(-2) h(-1) in October to 8.0 +/- 2.9 mg CH4 m(-2) h(-1) in August. The fen was generally a daytime sink for CO2, and net CO2 emission was only observed in late October. Variations in NEE were more pronounced than variations in CH4 emissions, but both fluxes correlated with changes in green C. rostrata biomass and subsurface temperatures. Methane and CO2 pore water concentrations also varied significantly over the snow-free period, decreasing and increasing, respectively. These variations were linked to the development of biomass, but CH4 emissions and NEE were not correlated with the respective pore water concentrations.