While dams have been presumed to have little, if no significant contribution to carbon emissions, a recent research study has shown critical contrary findings.
Apparently, dams have been underestimated as potential sources of CO2 emissions due to their efficiency as net carbon stores, while acting as reservoirs for potable water, agricultural irrigation and in the operation of hydropower plants. However, researchers from the Umwelt Forschungs Zentrum (UFZ) Helmholtz Centre for Environmental Research and Catalan Institute for Water Research (ICRA) scientists, conducted a study re-evaluating the role played by dams as part of the global cycle. The results of their study was published in Nature Geosciences las May 2021.
Why Dams are Capable of Releasing Large Amounts of Carbon
Dr Matthias Koschorreck, a biologist at the UFZ’s Department of Lake Research, said that for a long time, it has been presumed that dams store the same amount of carbon when released as components of greenhouse gasses. Dr.Koschorreck explained why this was not the case.
Streams tend to transport large amounts of algae, leaves and branches that contain carbon, which gradually accumulates at the bottom of dams. However, the degradation process of the carbon-carrying materials at the bottom takes longer to complete due to the lack of oxygen. That explains why less carbon is released when dams release greenhouse gas emissions, since some of the carbon of the undegassed sediments remain stored at the bottom of the water reservoir.
One of the UFZ researchers, Philipp Keller, a former PhD student, explained that in the event when areas dry up, they will release larger amounts of carbon when compared to the amounts released in areas still covered with water. This could occur when dams let out substantial amounts of water, to the extent of exposing large areas where the still ungassed sediments have amassed. Now here’s the thing, this particular aspect has not been considered in the calculation of carbon, which is the knowledge gap that was filled by the study.
How the Scientists Conducted Their Study
Using databases sourced from satellite imagery and focusing on dams as examples, the scientists were able to trace when, where and for how long 6,800 dams worldwide were filled with water and the size of the areas that became partly or fully exposed. Based on the information they gathered, the scientists found out that on the average, about 15% of the entire reservoir surface was not covered by water.
Upon calculation of the carbon released by the exposed areas, the underestimated portion had actually released twice the amount of carbon that the reservoir had stored. The scientists said that based on their calculations, there was significant underestimation of the carbon emissions produced by the dams. That being the case, the scientists recommend reconsideration about the general perception on the role played by dams as a net carbon store, in relation to the global carbon cycle.
Moreover, the data they evaluated revealed that fluctuations in water level can influence the global carbon balance, particularly in areas where dams are used for irrigation. Mainly because larger areas of such dams were frequently dry for longer periods.