According to international researchers led by Australia’s Southern Cross University, a new greenhouse gas budget shows that coastal ecosystems globally are a net greenhouse gas sink for carbon dioxide (CO2), while emissions of methane (CH4) and nitrous oxide (N2O) offset some of the CO2 intake.
The publication, Coastal vegetation and estuaries collectively comprise a greenhouse gas sink, published today in Nature Climate Change, summarises the new findings of the coastal greenhouse gas balance (CO2 + CH4 + N2O) in 10 globe regions and globally.
Many coastlines across the world exhibit tremendous variation in greenhouse gas sinks and outputs, ranging from tropical lagoons to frigid fjords, coastal mangrove forests to undersea seagrass beds.
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 human impact reduction actions, such as reducing fertiliser, organic matter, and wastewater inputs into coastal rivers, can reduce the amount of CH4 and N2O released into the atmosphere.
North America, South America, Europe, Africa, Russia, West Asia, South Asia, East Asia, Southeast Asia, and Australasia were among the ten globe regions studied by the international team of scientists .
They discovered Southeast Asia to be the most effective coastal greenhouse gas (GHG) sink due to its huge and prolific tropical coastal wetlands that absorb CO2. North America is a second sink hotspot, with significant expanses of coastal marshes as well as CO2-absorbing 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 Project to establish greenhouse gas budgets of large regions covering the entire globe, and for which the contribution of these coastal ecosystems remained unaccounted for,” said co-author Pierre Regnier, Professor of Earth System Science at Université Libre de Bruxelles.
Snapshot: Coastal Greenhouse Gas Sinks and Sources Around the World
To measure CO2, CH4, and N2O fluxes in estuaries and coastal vegetation in ten worldwide regions, a dataset of observations from 738 sites from research published between 1975 and 2020 was assembled.
GHG uptake and/or release from coastal systems is driven by special coastal features (climate, hydrology, abundance) in each place throughout the world.
The strongest coastal greenhouse gas sinks are:
Top: Southeast Asia’s archipelagic region, due to its extensive and productive tropical mangrove forests and seagrass beds that absorb large amounts of CO2.
North America is next because of its enormous expanses of salt marshes, mangroves, and seagrasses, as well as CO2-absorbing fjords.
Third, Africa has significant CO2 uptake by mangroves and seagrasses, which is somewhat offset by estuarine GHG emissions.
Moderate coastal sinks of greenhouse gases:
- South America: coastal wetlands, particularly mangroves, absorb moderate amounts of CO2 and emit some estuarine GHGs.
- Australasia contains long sections of CO2-absorbing coastal wetlands, but it also has a high number of estuaries along its coasts, many of which are a source of CO2, CH4, and N2O.
- West Asia has a low estuarine GHG supply and a moderate CO2 uptake by coastal wetlands, primarily seagrasses.
weak Coastal greenhouse gas sinks are :
- East and South Asia: estuarine GHG emissions significantly diminish the moderate coastal wetlands CO2 sink.
Weak coastal sources of greenhouse gases:
- Europe and Russia both emit more coastal GHG than they can absorb from the atmosphere. These areas contain many impacted tidal estuaries, which emit greenhouse gases; a cooler climate also implies less coastal wetlands (for example, mangroves), which would otherwise absorb enormous amounts of CO2.
Source: https://www.scu.edu.au/
