Consequences of dam removal for reservoir carbon storage and emissions

Because dams can facilitate high reservoir carbon emissions, reduced emissions have been proposed as a dam removal benefit; however, the impact of removal on carbon balance depends on several gas exchange pathways. We combined literature values with statistical and mechanistic models to estimate carbon balance in the reservoir footprint before, during, and after the removals of Veazie (ME, USA), Glines Canyon (WA, USA), and Simkins Dam (MD, USA). Before removal, we estimated that all reservoir footprints were likely net greenhouse gas sinks, with magnitudes ranging from -25.7 to -12300 Mg CO₂-eq yr^-1. Averaged over one hundred years following dam removal, we estimated that the Veazie and Simkins footprints would be sources of CO₂-eq (5110 and 91.2 Mg CO₂-eq yr^-1, respectively), while the Glines Canyon would be a weaker sink (-427 Mg CO₂-eq yr^-1). Our results indicated that a dam's geomorphic and ecological setting influenced changes in carbon balance, but all modeled removals reduced landscape-scale sequestration. Consistent with prior emissions measurements from drying reservoir sediments, our results suggested that reservoir sediment carbon is vulnerable to mineralization upon dam removal. Strategies to reduce erosion and grow vegetation in the reservoir footprint merit investigation for their potential to reduce dam removal-associated carbon emissions.