Beavers can convert stream corridors to persistent carbon sinks

Abstract Recent reintroductions of the Eurasian beaver ( Castor fiber ) across Europe represents an ecological shift with potential implications for carbon cycling in stream corridors. However, the capacity of beaver impacts to influence short- and long-term carbon fluxes, and the mechanisms that govern these changes, remains poorly understood. We present a comprehensive carbon budget of a beaver-influenced stream corridor, covering all major aqueous and atmospheric exchanges, as well as biomass and sedimentary carbon storages, from a beaver wetland in Switzerland. By integrating carbon flux measurements with hydrology and bathymetry, we identify dominant pathways and dynamics in gaseous carbon emissions. Annually, the beaver wetland was a net carbon sink (98.3 ± 34.4 t yr -1 ), driven by subsurface removal of dissolved inorganic carbon. Carbon dioxide emissions were the dominant source of carbon loss, seasonally shifting the system to a net carbon source during summer water recession. Projecting the long-term sediment and deadwood storage following wetland infilling, our upper estimate of sequestered carbon was 1194 t (10.1 t ha -1 yr -1 ), nearly an order of magnitude greater than without beaver modification. Our findings demonstrate that beaver-induced hydrological change is fundamentally reshaping carbon cycling and reinforces the relevance of headwater catchments in climate change mitigation strategies.