High spatiotemporal variation of CH4 and CO2 fluxes from inundated areas
in a temperate fen
Abstract
Peatland ecosystems are unsurpassed in their carbon-storing capacity.
However, they can be hotspots for emissions of greenhouse gases (GHGs)
depending on soil water saturation and oxygen status. Using automated
floating chambers, we investigated the spatiotemporal variability of CH4
and CO2 fluxes and their environmental drivers from inundated areas in a
temperate, rich fen. We distinguished between two areas: one with
continuous inundation, caused by upwelling groundwater and a lower-lying
area with periodic inundation by flooding from an adjacent stream. Using
hourly measurements, we found mean effluxes of CH4 and CO2 to be 0.16
and 1.23 g C m-2 d-1 between October and May with more than a 10-fold
variation between observations. For CO2, efflux were higher in the
periodically inundated area compared to the continuously inundated area.
In contrast, CH4 fluxes were higher, and dominated by ebullition, at the
area with continuous inundation. Both fluxes increased with soil
temperature and wind speed. Advective and diffusive fluxes of CH4 and
CO2 associated to groundwater upwelling and upwards diffusion of
dissolved gases from shallow groundwater (0.5-0.8 meters below ground
level) contributed negligibly to the measured fluxes, suggesting that
the emitted GHGs were produced close to the terrain. Our data highlight
the large spatiotemporal variation of CO2 and CH4 emissions from fens
due to variations in hydrology and topography affecting GHG production
near the soil surface. Particularly, the temporary dynamics of soil
inundation played a major role in controlling the contribution by CO2
and CH4 to wetland GHG release.