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 (CH 4 ) and carbon dioxide (CO 2 ). We provide an in situ study on variability of daytime CH 4 emissions and net ecosystem CO 2 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 CH 4 source throughout the snow-free period, and emissions varied significantly between the sampling dates, ranging from 3.1 ± 0.9 mg CH 4 m −2 h −1 in October to 8.0 ± 2.9 mg CH 4 m −2 h −1 in August. The fen was generally a daytime sink for CO 2 , and net CO 2 emission was only observed in late October. Variations in NEE were more pronounced than variations in CH 4 emissions, but both fluxes correlated with changes in green C. rostrata biomass and subsurface temperatures. Methane and CO 2 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 CH 4 emissions and NEE were not correlated with the respective pore water concentrations.