Greenhouse Gas Emission and Balance of Marshes at the Southern North Sea Coast

Abstract

Environmental parameters controlling fluxes of greenhouse gases (GHG) differ spatially within landscapes. This study aimed to improve the understanding of landscape processes controlling GHG-fluxes of different landscape units of marshes (in terms of vegetation, land use and seawater inflow) at the Southern North Sea coast. For this emissions of methane (CH₄) and nitrous oxide (N₂O) were quantified and related to reported carbon sequestration rates. Ancillary environmental parameters were determined to identify controlling factors and thresholds enabling GHG emissions. For inland marshes (enclosed by embankments) the water level was the predominant factor controlling CH₄ emissions ranging between 1.58 and 1544.70 kg CH₄ ha⁻¹ a⁻¹. The duration of threshold (10 cm below surface) exceedance was found as a predictor for annual CH₄ emissions. Emissions of outland marshes (influenced by tides) varying from −1.34 to 55.14 kg CH₄ ha⁻¹ a⁻¹ were predominantly controlled by sulphate ($\mathsf{S}{\mathsf{O}}_{\mathsf{4}}^{\mathsf{2}\hbox{-} }$) concentrations, because soil CH₄-contents were negligible when soil $\mathsf{S}{\mathsf{O}}_{\mathsf{4}}^{\mathsf{2}\hbox{-} }$-contents exceeded 0.5 mg g⁻¹. The variability of the N₂O-fluxes (−0.81 to 17.78 kg N₂O ha⁻¹ a⁻¹) could not be explained by the collected environmental parameters. GHG balances indicated that inland extensive grasslands and particularly reed stands are net sources of CO₂-equivalents (100 year time horizon), while outlands are natural sinks.