Estuaries’ vast potential for climate mitigation

The salt marshes, mud flats and eel grass meadows of temperate river estuaries are more effective at capturing and storing greenhouse gases than young coastal forests and may sequester carbon for centuries, if not millennia, according to researchers from the University of Victoria (UVic). The amount of carbon captured and stored, known as sequestered, by the Cowichan estuary on Vancouver Island is roughly double that of an actively growing 20-year-old Pacific Northwest forest of the same area, reports a new study published in the journal Frontiers in Marine Science . So-called blue carbon-carbon dioxide (CO2) captured from the atmosphere by marine plants and algae-collects as organic debris in estuary sediments where low-oxygen conditions prevent their decomposition. -Oxygen is depleted very quickly from the surface of the sediment due to aerobic microbial processes. This prevents buried organic matter from being remineralized back into CO2 and returning to the atmosphere,- says lead author Tristan Douglas, a UVic graduate student in the School of Earth and Ocean Sciences, who spent two years analyzing the physical and chemical properties of sediment cores collected from the Cowichan estuary. That makes undisturbed estuaries a potent passive carbon storage system with the global potential to capture and store greenhouse gas (GHG) emissions at the gigatons scale. Intertidal ecosystems-especially those in the tropics-can be 20 to 60 times more effective than forests at capturing and storing carbon dioxide.