Tracking global greenhouse gas emissions is necessary to accurately predict and manage effects of climate change. A recent study found that reservoirs are a larger source of greenhouse gas emissions than previously thought. The study, published in BioScience, found that reservoirs associated with dams release carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) to the atmosphere. The authors estimated that reservoirs across the globe release about 0.8 Pg of CO2 equivalents annually, 79% of which comes from CH4. This is higher than previous estimates, and indicates that our current global carbon budget is underestimated.
The authors also evaluated the reservoir characteristics that best predict carbon emissions. Previous work found that reservoir age and latitude were the best indicators of emissions. But this global analysis indicated that the best predictor was reservoir productivity, as measured by algal chlorophyll a concentrations. This is because reservoirs with higher algal concentrations provide more organic material for microbes to break down into CH4.
These findings are of major importance because dams continue to be built around the globe, with unintended consequences for carbon emissions. Furthermore, freshwaters worldwide are facing increased nutrient inputs, which increase algal levels, and will increase CH4 emissions in reservoirs. Overall, this new study highlights that mitigating effects of global climate change will need to account for carbon emissions released when we dam our waterways.
For other global analyses of freshwater carbon emissions, see: