Quantification and Isotopic Characterisation of Methane Emissions from Dutch Peatland Ditches - Flux Measurements and Isotopic Source Analysis

Abstract

Drainage of peatlands drastically reduces methane (CH4) emissions. However, artificially created ditches in these areas serve as hotspots for CH4 production, which offsets this effect. CH4 emissions from peatlands and especially their ditches contribute significantly to the global atmospheric CH4 budget, yet the spatial variability and the environmental factors controlling these emissions are not well understood. This research conducted CH4 flux measurements and isotope analysis of δ13C and δ2H across 7 locations within Dutch peatlands, which were either used for agricultural purposes or nature reserves. At each location, methane fluxes were measured at three positions: on the water surface of the ditch, on the saturated slope and the unsaturated adjacent land. The results show that the emissions are highly variable across the locations, with the highest fluxes observed at the water surface (between 0.05 and 24.8 mg/m2/min), followed by the ditch slope (between 0.00002 and 0.04 mg/m2/min) and the unsaturated land showing very small emissions. At the same three spots, samples were taken for isotopic analysis, which showed that methane emitted from water was most enriched in both 13C and 2H, indicating high levels of oxidation before reaching the water surface-air interface. High variability in isotopic composition was seen between locations, indicating that the methanogenic pathway highly depends on the local environmental characteristics. The isotopic composition of methane from the ditch slope was generally most depleted, suggesting anaerobic conditions within the soil. Additionally, land use and nutrient input were found to influence both methane production and isotopic composition, showing more enriched methane emitted from locations used for agricultural purposes (-62.8‰ δ13C and -247.3 ‰ δ2H), compared to nature reserves (-60.3 ‰ δ13C and -309.0‰ δ2H). This research highlights the importance of considering local environmental circumstances, groundwater level, land use and nutrient input when assessing and modelling methane emissions. The findings improve the understanding of methane dynamics at a local scale within peatlands and may contribute to improving models, which often still overgeneralise methane emissions from peatlands.