Among other things, dams serve as reservoirs for drinking water, agricultural irrigation, or the operation of hydropower plants. Until now, it had been assumed that dams act as net carbon stores.
Among other things, dams serve as reservoirs for drinking water, agricultural irrigation, or the operation of hydropower plants. Until now, it had been assumed that dams act as net carbon stores. Researchers from the Helmholtz Centre of Environmental Research (UFZ) together with Spanish scientists from the Catalan Institute for Water Research (ICRA) in Girona and the University of Barcelona showed that dams release twice as much carbon as they store. The study has been published in Nature Geosciences.
Whether leaves, branches, or algae - streams transport large amounts of carbon-containing material. If the water is dammed, the material gradually settles and accumulates at the bottom of the body of water. "Because of the lack of oxygen, the degradation processes are much slower down there. As a result, less carbon dioxide is released. The carbon contained is stored in the sediment of the dam for a longer time", explains Dr Matthias Koschorreck, a biologist in the Department of Lake Research at the UFZ. "It had been assumed that dams store about the same amount of carbon than they release as greenhouse gases".
However, for the carbon balance of bodies of water, not only the zones covered by water - but also those that temporarily dry out because of a drop in the water level - play a role. Koschorreck’s working group had demonstrated this in previous studies. If the carbon-containing material previously covered by water comes into contact with atmospheric oxygen, degradation processes and thus the formation of carbon dioxide are strongly driven. "Areas of water that are drying out thus release considerably more carbon than areas covered by water", says Philipp Keller, a former PhD student in the Department of Lake Research at the UFZ. "If large amounts of water are released by a dam, large areas are suddenly exposed. But these areas had not been considered when calculating the carbon balance. This is the knowledge gap that we close with our work".
Read more at: Helmholtz Centre for Environmental Research - UFZ
The Eder dam (Germany) in the year 2019. Areas of water that are drying out release considerably more carbon than areas covered by water. (Photo Credit: Maik Dobbermann)