Groundwater level controls CO2, N2O and CH4 fluxes of three different hydromorphic soil types of a temperate forest ecosystem.

Hydromorphic soils should exhibit higher climate change feedback potentials than well aerated soils since soil organic matter (SOM) losses in them are predicted to be much larger than those of well aerated soils. To evaluate a combined feedback relationship between groundwater level (GWL) and total greenhouse gas (GHG) emission, a greenhouse microcosm experiment was performed by exposing three hydromorphic forest soil types that differed in carbon content to three water levels (−40, −20 and −5 cm) while plants were excluded. Net GHG fluxes were measured continuously. GHG concentrations plus oxygen were measured in soil air and soil water at different depths. In this study, soil type hardly affected GHG emissions but GWL did. CO2 emissions peaked at GWL of −40 cm and declined on average to 65 and 33% during GWL at −20 and −5 cm, respectively. CH4 emissions showed the opposite pattern having the highest emission rates at GWL of −5 cm and compared to that on average only −3 and −8% during GWL at −20 and −40 cm, respectively. The highest mean N2O emissions were detected at the intermediate GWL of −20 cm, whereas it is reduced on average to 18% for GWL at −40 cm and at −5 cm. The highest greenhouse gas emissions (in CO2 equivalents) were calculated for GWL at −20 cm. During GWL at −40 cm, CO2 equivalent fluxes were only insignificantly lower. CO2 equivalent fluxes reduced explicitly in mean to 35% with GWL at −5 cm. The outcome emphasizes that anaerobic SOM decomposition apparently produces a lower warming potential than aerobic SOM decomposition. Undoubtedly, hydromorphic soils have to be considered for climate–carbon feedback scenarios.