The drawdown phase of dam decommissioning is a hot moment of gaseous carbon emissions from a temperate reservoir

Dam decommissioning (DD) is a viable management option for thousands of ageing dams. Reservoirs are large carbon sinks, and reservoir drawdown results in important dioxide (CO2) methane (CH4) emissions. We studied the effects DD on CO2 CH4 fluxes from impounded water, exposed sediment, lotic water before, during, 3–10 months after Enobieta Reservoir, north Iberian Peninsula. During study period, covered 0–100%, sediment 0–96%, 0–4% total area (0.14 km2). Areal (mean [SE]: 295.65 [74.90] mmol m?2 d?1) (188.11 [86.09] decreased over time but remained higher than (?36.65 [83.40] d?1). did not change were noteworthy only (1.82 [1.11] Total ecosystem (CO2 + CH4) (kg CO2-eq during before because sediment. The was net sink became an emitter first 10 drawdown. Future studies should examine mid- long-term fluxes, identify drivers areal incorporate footprint reservoirs.