Australian marine scientists say a rethink of how we protect and restore coastal wetlands is needed after a global analysis found much of the organic carbon locked in their soils originates beyond the wetlands themselves.
In a study published in Global Change Biology, researchers from the Australian Institute of Marine Science (AIMS) developed a mathematical model to standardise and interpret hundreds of measurements from soils beneath saltmarsh, mangrove and seagrass habitats around the world. The work teases apart the sources of organic carbon in these “blue carbon” ecosystems, which are valued for their ability to store carbon for centuries.
Lead author and AIMS research scientist Dr Chris Fulton said the picture that emerged challenges a long‑held assumption about where most buried carbon comes from. “While the source of the organic carbon varied a lot depending on the location and conditions, we found that generally more than half the organic carbon stored in these soils came from plants outside of the wetland – things like seaweeds and land plants growing offshore and upstream,” he said.
“This means we need to start thinking about these blue carbon wetlands as part of a connected matrix. We can’t just protect mangrove forests; we need holistic coastal management to protect a diversity of organic carbon sources.
” He added: “This work also shows we can enhance this blue carbon sequestration by understanding how a spread of plants in the seascape will contribute more carbon to a restored coastal wetland.”
The findings indicate that management and restoration that only focus on the habitat‑forming plants could miss a significant portion of the carbon supply delivered from elsewhere in the catchment and coastal zone. That has implications for the design of projects aimed at boosting carbon sequestration and for carbon accounting frameworks.
Dr Fulton said the work comes as governments and markets look for credible, nature‑based carbon storage options. “One of the oldest carbon capture and storage technologies is the mangrove forest, which we’ve just discovered not only stores organic carbon from itself but also grabs carbon from all around it and buries it in the soil for centuries,” he said. “Excess carbon in our atmosphere is the root cause of climate events: from the marine heatwaves that have so clearly affected Australia’s marine ecosystems recently to the floods and fires that occur across our continent.
” “So, what can we do? Help our coastal plants to continue burying carbon in the soil while we also do our best to reduce greenhouse gas emissions.
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He also called for policy updates. “Our findings also highlight the need to update blue carbon crediting systems—both in Australia and internationally—which are focused on the plants that create the wetlands and ignore other important sources of carbon sequestration.”
Fieldwork underpinning the model included soil coring in mangroves at Mangrove Bay, near Exmouth in Western Australia. The research sits within AIMS’ Blue Carbon Seascapes Project, led by Dr Fulton and jointly funded by BHP, which aims to build seascape‑scale models that account for all potential carbon sources and pathways across connected coastal habitats.
The paper, Tracing blue carbon flows across diverse seascapes, is available at: https://doi.org/10.1111/gcb.70420.
