Flooding of an abandoned fen by beaver led to highly variable greenhouse gas emissions

Rewetting by beaver is reported from many European peatlands and especially from Belarus, which harbours vast abandoned peat extraction sites and a large beaver population. We studied how vegetation and exchange rates of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) changed after beaver had rewetted an abandoned drained fen in Belarus. We selected three sites with different vegetation and water levels. One meadow site turned into a nutrient-poor lake that remained virtually free of living vascular plants, released CO2 and CH4, and was a moderate source of greenhouse gases (GHG). In another meadow site that became shallowly flooded, the died-off vegetation was quickly replaced by mire plant species and in the second year the site had already become a strong CO2 sink, a moderate CH4 source and, as a result, a strong carbon sink and a weak net GHG emitter. The third site was dominated by forbs that died after intermittent flooding and were only slowly and sparsely replaced by wetland species. This site was a strong source of CO2 and N2O. Beaver activity can restore a peatland's carbon sink and reduce GHG emissions. However, as for humaninduced rewetting, the outcome depends on starting conditions, position and constancy of the water level, and the time needed for establishment of peat forming vegetation.