Influence of rewetting on N2O emissions in three different fen types.

In recent years, many peatlands in Europe have been rewetted for nature conservation and global warming mitigation. However, the effects on emissions of the greenhouse gas nitrous oxide (N₂O) have been found to be highly variable and driving factors are poorly understood. Therefore, we measured N₂O fluxes every two weeks over three years on pairs of sites (one drained, one rewetted) of three important peatland types in North-Eastern Germany, namely, percolation fen, alder forest and coastal fen. Additionally, every three months, sources of N₂O were determined using a stable isotope mapping approach. Overall, fluxes were under the very dry conditions of the study years usually small with large temporal and spatial variations. Ammonium concentrations consistently and significantly correlated positively with N₂O fluxes for all sites. Cumulative fluxes were often not significantly different from zero and apart from the rewetted alder forest, which was always a source of N₂O, sites showed varying cumulative emission behavior (insignificant, source, potentially sink in one case) among years. Precipitation was positively correlated with cumulative fluxes on all drained sites and the rewetted alder forest. Isotope mapping indicated that N₂O was always produced by more than one process simultaneously, with the estimated contribution of denitrification varying between 20 and 80%. N₂O reduction played a potentially large role, with 5 to 50% of total emissions, showing large variations among sites and over time. Overall, neither the effect of rewetting, water level nor seasonality was clearly reflected in the fluxes or sources. Emissions were concentrated in hotspots and hot moments. A better understanding of the driving factors of N₂O production and reduction in (rewetted) fens is essential and stable isotope methods including measurements of ¹⁵N and ¹⁸O as well as site preferences can help foster the necessary comprehension of the underlying mechanisms.

Supplementary information: The online version contains supplementary material available at 10.1007/s10705-022-10244-y.