Ambitious wetland habitat restoration projects could usher in a bright future for natural carbon sequestration and storage.
They are Earth’s natural carbon sinks — living coastal ecosystems such as mangroves, salt marshes and seagrass beds — that can store to four times the amount of carbon compared to mature tropical rainforests.
Initiatives to restore living coastal ecosystems — collectively known as “blue carbon” — are becoming powerful weapons in the race to combat rising greenhouse gas emissions.
Not only do they sequester carbon dioxide faster than terrestrial forests and hold it for much longer, but they also protect against coastal erosion and other direct effects of climate change.
While coastal habitats cover two per cent of the ocean’s surface and store around half of the total carbon sequestered in ocean sediments, they are also some of the most threatened ecosystems on Earth.
Globally, some 90 per cent of wetlands has been lost since 1700, with around 70 per cent of destruction occurring since 1900. At the current rate of destruction, 40 per cent of the remaining tidal marshes and seagrasses could be lost over the next century, along with almost all the remaining unprotected mangroves.
Destruction of these habitats — through drought, overfishing and urban development — can be catastrophic for both the local environment and community, but it can also drive up carbon emissions.
Two severe cyclones in the Gulf of Carpentaria in 2018 and 2019 that decimated important mangrove forests resulted in more than 850,000 t of carbon released into the atmosphere — the equivalent of about 2000 commercial flights from Sydney to Paris.
With the ocean’s ability to capture carbon dioxide from the atmosphere gaining increasing attention around the world, the Australian government announced $9.5 million last year to support five new practical restoration projects in blue carbon ecosystems in Queensland, South Australia and Tasmania, and a further $3 million for four projects in Indonesia and Papua New Guinea.
At the 2022 United Nations Climate Change Conference in Egypt, the CSIRO, the Department of Foreign Affairs and Trade, and Google Australia unveiled a collaboration relying on machine learning to model blue carbon in the Indo-Pacific and along Australia’s coastline as part of the tech giant’s Digital Future Initiative.
“Australia has one of the longest coastlines on Earth and is home to about 12 per cent of the world’s blue carbon,” said Minister for the Environment and Water Tanya Plibersek when she announced the funding for the Indonesia and Papua New Guinea projects.
“So we very much understand the importance of protecting, restoring, expanding these environments.”
Lay of the land
A number of other blue carbon projects are underway, with universities and research organisations still learning best practices for a term that was only first coined in 2009.
Given that valuing blue carbon sequestration may help encourage restoration projects, rigorous methods are required to quantify the amount of blue carbon sequestered in coastal wetland restoration.
“The first blue carbon method that can be implemented through Australia’s Emission Reduction Fund is tidal flow restoration to areas where the tide has previously been restricted,” said Dr Paul Branson, an engineer and coastal oceanographer with the CSIRO.
Branson is working on a $3.3 million, 30-month mission estimating Australia’s blue carbon potential, where researchers will measure and quantify the emissions reduction capacity of Australia’s mangroves, seagrasses and tidal marshes.
“In many locations, coastal saltwater marshes have been bunded for salt production or drained for grazing or agricultural purposes,” he said.
“The changes in the hydrology of these systems results in the loss of coastal ecosystems and release of carbon due to soil degradation. Through reconnecting the tidal hydrodynamics and flushing, coastal ecosystems are able to re-establish, allowing the system to become a net carbon sink.
“The tidal re-introduction process typically involves land surveying, hydrological studies and engineering earthworks to remove bunds and tidal restrictions.”
Describing the joint CSIRO and BHP project as “ambitious”, Branson said that his role as a coastal engineer is twofold.
“Firstly, to use models and measurements of water levels around Australia to estimate mean sea level and tidal planes relative to a national vertical datum. These water levels feed into models that estimate the current and potential future carbon abatement, whilst also considering land uses and future sea-level rise,” he said.
“The second component is assessing the coastal risk reduction benefits that these systems provide through the attenuation of waves and storm surges.”
In setting out to answer how long blue carbon projects can take to see meaningful change, Branson cautioned that it is only possible with further investment, including in helping proponents collect the necessary data from multiple sources, learning from past projects and improving engineering design to enhance the recolonisation process.
“We currently don’t have a national-scale estimate of the potential of blue carbon, or land available for tidal re-introduction,” he said.
“If the hydrological conditions are right, and seeds available or replanting undertaken, mangrove biomass can increase quite rapidly over the first 10 years.”
Pilot projects are currently underway, and monitoring has demonstrated that soil carbon levels can increase after only two to three years.
“However, the overall re-establishment process is long term, which is why the Emissions Reduction Fund method considers timescales of up to 100 years,” he said.
Minalee Busi is a systems engineer and analyst on the Climateworks Centre’s Southeast Asia Framework for Ocean Action in Mitigation, or SEAFOAM, project, which is using Indonesia as a pilot project in trying to understand the climate change mitigation potential of the ocean, including blue carbon ecosystems.
“It’s a mapping exercise in terms of understanding where these ecosystems exist in and around Indonesia,” she told create.
“We’re also analysing the emissions reduction potential of these ecosystems as well as highlighting gaps in the data that currently exist.”
Using an application called ArcGIS to map these ecosystems across Indonesia, the project aims to provide policy recommendations to the Indonesian government, which will be able to demonstrate it leadership in protection and restoration of these sites.
“There’s been a lot of focus on mangroves as an important blue carbon sink, but we have found much less attention and prioritisation given to seagrass ecosystems,” Busi said.
One challenge is that there are many disparate sources of information, and the aim is to present the most up-to-date and accurate data by focusing on ground truth validated data.
This includes the sediment carbon storage potential of seagrass ecosystems, for example, to understand the actual potential of carbon storage of these ecosystems, as well as quantifying the climate change mitigation potential from protection and restoration of these ecosystems.
“We hope to increase ocean-climate literacy by providing information about the importance of these ecosystems in mitigating climate change, and work with on-ground partners in the future to improve technical expertise required for the development of these projects,” Busi said.
“We are beginning to see huge interest from financial institutions, who are understanding the value of oceans and blue carbon ecosystems for a low carbon environment, as well as the role they play in provisioning financial incentives required to make these projects self-sustaining.”
At the University of New South Wales’s Water Research Laboratory, Toby Tucker CPEng is a senior engineer looking at wetland hydrology and the hydraulic design of wetland systems.
“My work on coastal wetland restoration and coastal floodplains has looked at the loss of these environments since European settlement,” he told create.
“They’ve been over-drained and there hasn’t always been a lot of thought put into what these habitats actually provide for the environment.”
After first coming to the field through work on severely degraded coastal floodplain systems, he now works on blue carbon by calculating how engineers can manipulate what was formerly agricultural or poorly drained systems and how we can change how water flows across those sites to create new habitats.
One key project he has been involved in is the Yeramba Lagoon in the Georges River in the south-west of Sydney.
About 80 years ago, construction of a roadway disconnected the lagoon from the estuary, and this has seen the waterway suffer an accumulation of contaminants and poor tidal flushing.
“In that time, lots of runoff from the urban environment saw a dense weed mat grow across the site,” he said.
In looking for ways to restore the lagoon to its former state, engineers at the laboratory conducted numerical modelling, which informed the design of what needed to be done to restore the area.
Tucker is now monitoring the system following its restoration to assess how successful they have been at getting the tide back into the system.
“Part of our work was understanding if we could create the right hydrological conditions for blue carbon habitat to grow, since when blue carbon vegetation like saltmarsh mangrove and seagrass grow, they capture carbon,” he said
Some blue carbon habitats are harder to establish than others, with seagrass meadows in particular requiring a lot of additional work compared to mangroves.
“At Yeramba, this hydrological assessment was completed as part of the numerical modelling,” Tucker said.
“Importantly though, there are other blue carbon habitats on the Georges River nearby, so their seeds can flow into Yeramba
Lagoon on incoming tides and establish new vegetation.”
Tucker describes this kind of engineering as “conceptual”, in that he considers how the site behaves in terms of hydrology and hydraulics, and what changes are needed.
On projects such as the Tomago Wetland restoration project in the lower Hunter River estuary of New South Wales, he works closely in conjunction with other engineers who determine design, materials and construction.
“Researchers are looking at the wetlands’ capacity to take nutrients and carbon through the groundwater as well as the surface water,” he said.
“One of the big themes in blue carbon recently is not only focusing on carbon capture, but the other ecosystem services and co-benefits that are provided by coastal wetland habitats.
“There’s a lot more benefit to be gained than just the carbon that’s been stored — such as removing nutrients from the waterway, increasing biodiversity, establishing good fishery nurseries, and flood protection by attenuating wave energy or acting as storage basins for flood events.
“It’s so exciting that blue carbon is a pathway towards recognising the value of coastal wetland habitats.”