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Drying Lakes Can Release the Carbon Buried Beneath Them
A new study published in Science examines how the destruction of the Aral Sea changed the carbon balance of Central Asia.
Lakes accumulate organic material in their sediments over long periods, effectively burying carbon beneath the water. When a lake dries, those sediments become exposed to oxygen. The stored organic material begins decomposing and releases carbon dioxide back into the atmosphere.
Researchers estimate that the exposed Aral Sea bed has released approximately 748 million metric tons of carbon dioxide since 1960. About 90 percent of the lake has disappeared after the rivers feeding it were diverted for large-scale irrigation.
The study estimates that another 605 million metric tons of carbon dioxide could eventually be released from the remaining exposed sediments. Reflooding part of the former lakebed could slow or prevent those emissions while restoring some of the lake's ability to store carbon.
We usually discuss disappearing lakes as water, habitat, dust and public-health disasters. This research adds another consequence: a lakebed can become a massive carbon source after the water is gone.
The Aral Sea is an extreme example, but it is not the only one. Researchers warn that drying at the Great Salt Lake, Salton Sea, Lake Urmia, Lake Chad and Caspian Sea could produce similar changes that are still largely missing from climate accounting.
Protecting and restoring lakes may therefore be more than water conservation. It may also prevent carbon stored over generations from returning to the atmosphere.