Diurnal Patterns of Greenhouse Gas Fluxes in a Swiss Alpine Fen

Abstract

Diurnal patterns of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) 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 −2 h −1 in August). The fen was a nighttime CO 2 source (138 ± 46 mg m −2 h −1 ) and generally a daytime CO 2 sink. Uptake of CO 2 varied with light intensity (98 ± 57 to 391 ± 43 mg m −2 h −1 in August), but light saturation of photosynthesis was apparent at low irradiation levels. Emission or uptake of N 2 O was not discerned. In September, CH 4 and CO 2 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 CH 4 and CO 2 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 −2 day −1 ), but high CH 4 emissions resulted in the fen being a net source of 250 mmol CO 2 equivalents m −2 day −1 . Keywords Methane . Carbon dioxide . Wetlands . Carex rostrata . Flux chambers * Josef Zeyer

High spatiotemporal variation of CH4 and CO2 fluxes from inundated areas in a temperate fen

“…Outside the growing season and on bare soils, diurnal temperature fluctuations may be pronounced and contribute to the diurnal variation as well. Studies on diurnal variation in CH 4 fluxes show divergent findings with larger effluxes during either day or night or no distinct diurnal patterns (Bansal et al, 2018;Ding et al, 2004;Henneberger et al, 2017;Martin & Moseman-Valtierra, 2017). As these light-dark patterns likely differ depending on site, peatland type and season, many measurements at high temporal resolution are required for a reliable evaluation of the carbon emission.…”