Researchers at the University of Victoria have discovered the potential for temperate river estuaries (shallow basins of water where rivers meet the sea) to store greenhouse gas for centuries, if not millennia.
The amount of carbon sequestered by salt marshes and eelgrass meadows in the Cowichan estuary, for example, is double that of the actively growing 20-year-old forest in the same area, according to a data from a UVic study recently published in the journal Frontiers in Marine Science.
Carbon dioxide collects as “organic debris” in estuary sediments, where low-oxygen conditions prevent their decomposition into the atmosphere. As such, the passive carbon storage of undisturbed estuaries has the potential to capture greenhouse gases on a global, gigaton scale, the study states.
Tristan Douglas, the study’s lead author and a graduate student in the School of Earth and Ocean Sciences, spent two years analyzing the physical and chemical properties of the Cowichan estuary. Its aerobic microbial process quickly depletes oxygen from the surface of the sediment, he said in a release.
“This prevents buried organic matter from being re-mineralized back into CO2 and returning to the atmosphere,” he said.
However, damaged estuaries can and do release carbon on a similarly fantastic scale, Douglas noted. The study shows human activities have reduced the carbon capture and storage capacity of the 466-hectare Cowichan-Koksilah Estuary by about 30 per cent – equivalent to putting 53 gasoline-powered motor vehicles back on the road.
Log hauling and storage, and drainage for farming and cattle pastures during colonization were found to be the primary causes of the estuary’s damage. Researchers said the estuary’s restoration should begin on two fronts: replanting eelgrass to undo industrial activity, and opening the dikes that prevented ocean water from reaching now pasture land.
“We need to be looking at these kinds of nature-based solutions to mitigate the impact of CO2 emissions on our climate,” said study co-author, Ocean Networks Canada chief scientist and UVic professor Kim Juniper.
Policymakers should take note of the triple impact of undisturbed and restored estuaries, said the researchers; wetlands act as a buffer against floodwaters in the spring and as nurseries for aquatic species from crabs to salmon, in addition to reducing atmospheric greenhouse gas emissions.
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