German researchers identified a link between the sediment trapped behind hydroelectric dams and the release of methane in the atmosphere from rivers. In their study, published in the journal Environmental Science & Technology, the scientists established that the amount of the greenhouse gas released from the sediment might significantly increase the global freshwater emissions.
The authors looked into the effect of damming on methane emissions. The study was based on the fact that methane is one of the main contributors to heat trapping in the atmosphere, and that inland waters account for nearly 18% of global methane emissions.
The team gathered data from six small dams located in central Europe and established statistical relationships between methane concentrations and sedimentation in reservoir reaches.
The findings indicate that the more sediment is accumulated, the more methane is produced, due to the trapping by dams, crating methane emission hotspots. If all methane is released in the atmosphere, the authors suggest that it could result in as much as 7% increase of global freshwater emissions.
In times when energy generation and water shortages are of pressing concerns, the authors predict that more dams will be constructed in the near future, causing a huge increase in emissions. On a positive note, the team identified sediment accumulation as a suitable proxy for estimating methane emissions.