Coastal Ecosystems Act as a Net Greenhouse Gas Sink for Carbon Dioxide

Monday - June 5 2023, 03:43 UTC - 1 year ago

Researchers from Australia’s Southern Cross University have found that coastal ecosystems around the world act as a net greenhouse gas sink for carbon dioxide (CO2). Their recently published study in Nature Climate Change has revealed that emissions of methane (CH4) and nitrous oxide (N2O) partially counterbalance the CO2 absorption; however, on balance, these coastal ecosystems are still a vital sink for the global climate. In addition, the research team found that the strongest coastal greenhouse gas (GHG) sink is in Southeast Asia and that fjords around the world take up 40% of the carbon dioxide that would otherwise be released from tidal systems, deltas, and lagoons. The team's findings are set to inform the Global Carbon Project’s RECCAP2 initiative, which is aimed at encouraging better stewardship of coastal carbon managed by governments and local stakeholders around the world.

Coastal ecosystems, ranging from mangroves to fjords, have the ability to absorb or release greenhouse gases. However, on a global scale, these ecosystems are a vital sink. International researchers, led by Australia’s Southern Cross University, have revealed in a recent study that coastal ecosystems worldwide act as a net greenhouse gas sink for carbon dioxide (CO2), as per a new greenhouse gas budget .

However, the study also highlights that emissions of methane (CH4) and nitrous oxide (N2O) partially counterbalance the CO2 absorption. The new findings of the coastal greenhouse gas balance (CO2 + CH4 + N2O), encompassing ten regions globally, were recently published in the journal Nature Climate Change. From tropical lagoons to polar fjords, from coastal mangrove forests to underwater seagrass communities, many coastlines around the world show high diversity in greenhouse gas sinks and emissions .

"Understanding how and where greenhouse gases are released and absorbed in coastal ecosystems is an important first step for implementing effective climate mitigation strategies," said lead researcher, Dr Judith Rosentreter, Senior Research Fellow at Southern Cross University. "For example, protecting and restoring mangrove and salt marsh habitats is a promising strategy to strengthen the CO2 uptake by these coastal wetlands .

" Other activities to curb human impact, like reducing nutrients, organic matter, and wastewater inputs into coastal waterways, can reduce the amount of CH4 and N2O released into the atmosphere. The global team of scientists looked at ten different world regions: North America, South America, Europe, Africa, Russia, West Asia, South Asia, East Asia, Southeast Asia, and Australasia. They found the strongest coastal greenhouse gas (GHG) sink was in Southeast Asia because of its extensive and productive tropical coastal wetlands that take up CO2 .

A second sink hotspot is North America, with its large areas of coastal wetlands but also CO2-uptaking fjords. "Our new research shows that fjords around the world take up ~40% of CO2 that would otherwise be released from tidal systems, deltas, and lagoons. Most (86%) of this important CO2 uptake by fjords comes from the North America region, mostly Greenland," said co-author Professor Bradley Eyre, Professor of Biogeochemistry at Southern Cross University .

Dr. Rosentreter added: "Other coastal habitats are sources of greenhouse gases. For example, coastal wetlands such as mangrove forests, coastal salt marshes, and seagrasses, release more than three times more CH4 than all estuaries in the world." At the same time coastal wetlands, also called coastal ‘blue carbon’ wetlands, can be strong sinks of CO2 and some also take up N2O, which, on balance, makes them a net GHG sink for the atmosphere when all three greenhouse gases are considered .

"In our new study, we show that when we consider all three greenhouse gases (CO2 + CH4 + N2O), eight out of the 10 world regions are a coastal net greenhouse gas sink," Dr. Rosentreter said. The findings will inform the efforts of the Global Carbon Project’s RECCAP2. "The research was initiated by the Global Carbon Pacts’ Regional Carbon Capacity 2 initiative. RECCAP2 aims to encourage better stewardship of coastal carbon managed by governments and local stakeholders," said Dr .

Rosentreter.