Diurnal Patterns of Greenhouse Gas Fluxes in a Swiss Alpine Fen

Diurnal patterns of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) net fluxes were studied in a permanently submerged, Carex rostrata dominated Swiss alpine fen. Fluxes were measured in August and September using static chambers. Methane was emitted at all six time points analysed during each diurnal cycle with little variation between day, night or twilight (8.3 ± 0.8 mg m−2h−1 in August). The fen was a nighttime CO2 source (138 ± 46 mg m−2h−1) and generally a daytime CO2 sink. Uptake of CO2 varied with light intensity (98 ± 57 to 391 ± 43 mg m−2h−1 in August), but light saturation of photosynthesis was apparent at low irradiation levels. Emission or uptake of N2O was not discerned. In September, CH4 and CO2 fluxes were generally lower compared with August, compliant with less green C. rostrata biomass. Diurnal changes in subsurface properties were minor with little influence on the diurnal patterns. Temperature dependency of CH4 and CO2 emissions was apparent under controlled conditions using C. rostrata monoliths. In August, the fen showed highest photosynthetic rates and was a net carbon sink (50 mmol m−2day−1), but high CH4 emissions resulted in the fen being a net source of 250 mmol CO2 equivalents m−2day−1.