Wetlands win-win
Restoring coastal wetlands is not just a biodiversity win – it would lock away more carbon, limit managed retreat, and help revive Māori knowledge. Katy Jones reports.
‘‘You might have to have less managed retreat because the wetlands are actually offering natural protection from storm surge and sea level rise.’’
New Zealand’s blue carbon potential is just starting to be unearthed.
The term blue carbon was coined in 2009 for the carbon dioxide captured by oceans and coastal ecosystems, notably mangroves, seagrass meadows and salt marshes.
Some of those habitats globally have been found to sequester many times more carbon per unit than forest on dry land.
Their waterlogged soils lack oxygen, meaning plant material decomposes in those soils far more slowly, and the carbon in the material gets locked away for long periods – unless disturbed.
Some countries include blue carbon in their Nationally Determined Contributions – action plans for reducing national emissions and adapting to climate change.
In others, blue carbon credits have been awarded to groups funding the restoration of coastal ecosystems, and there are calls for a similar incentive scheme in New Zealand.
A vital step in the process is knowing how much carbon is being sequestered, but amounts can vary between coastal sites, due to environmental factors.
While some research has been carried out on carbon levels in New Zealand’s coastal ecosystems, a project to start measuring that in the top of the South Island has been recognised by the Government as among key action being taken across communities to tackle climate change.
The pilot project has so far taken samples from two sites:
the saltmarsh of Waimea Inlet, off the coast of Nelson; and the country’s largest area of seagrass, about 100km further north at Farewell Spit.
The pilot was initiated by the Tasman Environmental Trust, after the group invited the Department of Conservation’s technical adviser on blue carbon, Helen Kettles, to speak at a hui in the region in 2020.
Kettles says scientists have undertaken a few studies on blue carbon in New Zealand.
But she is excited that, rather than just a scientist carrying out the research, here was a group representing many parts of the community that
was already restoring coastal wetlands, taking the lead with a study they hoped would help people see the value of the wetlands, and ‘‘supercharge’’ restoration.
The top of the South has an abundance of coastal wetlands to boot, says Kettles, who is also an adviser on estuaries, climate change and coastal sediment.
‘‘I feel like it’s the right people in the right place at the right time.’’
The science organisation Cawthron Institute, based in Nelson, was part of the ‘‘Core and Restore’’ project, along with several local iwi and environmental groups – some of whom had provided funding, as had Nelson City Council.
Project lead Lauren Walker says the deepening climate crisis spurred the action, to highlight the need to protect and restore the coastal habitats. ‘‘We wanted to just get stuck in and do it now with all the amazing partners we’ve got locally, because we’re actually in the middle of the crisis.
‘‘I don’t feel like we can wait until some unknown body comes along to fund a big programme or come up with the right policy, or form a dataset.’’
Kettles says estuaries are rare ecosystems with special biodiversity that needs protection. ‘‘Coastal wetlands store huge amounts of carbon, they’re sequestering and locking it up infinitum.
‘‘They also protect shorelines from storm surges, so they’re going to protect us from some of the ravages of climate change at the coast.
‘‘They’re great for biodiversity, they also trap sediment. They’re really a winwin kind of thing.’’
But the ecosystems themselves and the endangered species they were home to were under threat from climate change, and pollution.
Extensive areas of marsh at river mouths around the country have been engineered to keep the sea out, to make way for agriculture and urban development, Kettles says.
While sea level rise was a pressure on our coasts, it was also an opportunity, she said.
For example, on marginal farmland that had become unviable.
‘‘There are places where we could say we are going to let the sea come in now, and we are going to start farming carbon.’’
Some plants would float in with the tide and re-establish themselves naturally, Kettles said.
‘‘Some of them you’ll introduce. That’s where you can get some huge wins, because you are actually restoring whole, bigger areas.’’
If managed retreat was being organised for a community, having coastal wetlands at the
margins could be of even
greater benefit.
‘‘You might have to have less managed retreat because the wetlands are actually offering natural protection from storm surge and sea level rise.’’
Tasman Environmental Trust chairperson Gillian Bishop says ex-cyclone Fehi in 2018 is a ‘‘stunning example’’ of the damage storm surge could do in areas without protection from coastal wetlands.
‘‘The sea came up a long way . . . we found driftwood 20 metres up from the normal high-tide mark in some places.’’
Trust-organised projects had restored more than 10km of the estuary margin in Waimea Inlet, with the saltwatertolerant coastal ribbonwood shrub the most planted species.
‘‘We found that where there was a good margin with coastal ribbonwood and so forth, the storm surge was abated. The damage wasn’t as great as it would have been if it had just had unimpeded capacity to flow in.’’
The pilot to measure carbon in the region’s coastal wetlands will help make informed decisions around managing and restoring them, Bishop says.
‘‘We can use that information to protect them, because . . . every time we disturb the carbon – the estuary edge or the wetlands – they leak carbon into the atmosphere.
‘‘Also, we need information that helps us make decisions about where best to place our restoration activities. And not only at the estuary edge but in the streams and catchments.’’
The project also provides a way of talking to owners of land that is potentially to be inundated by sea level rise, she says. ‘‘Instead of seeing it [the
land] as a problem and wanting to fill it or put in a wall, they can see that potentially there’s a value in that land.’’
Coastal ecologist Leigh Stevens says most of the extensive area of salt marsh and coastal wetlands surrounding the Waimea Inlet has been converted into functional pasture and farmland.
A lot of ‘‘low value’’ farmland there, and in estuaries around New Zealand would ‘‘benefit enormously’’ from reverting to salt marsh, he says.
Estuary ecosystems provided a very good natural buffer to coastal erosion, dampening wave energy, trapping sediment that harmed fish and other species, and filtering out nutrients which could cause nuisance algal blooms.
Stevens says more salt marsh would be lost in estuaries across New Zealand if it wasn’t allowed to migrate.
Seawalls and floodgates had been built in estuaries to
prevent tidal waters from coming in.
‘‘As sea levels inevitably rise, the salt marsh, which can only live in a very narrow band at the top of the estuary margin, is going to get inundated to the point that it can no longer grow.’’
It was very expensive to construct and maintain structures to provide the same services as estuaries naturally did, especially in the face of sea level rise, which would involve continually updating and moving those structures.
‘‘And often . . . they will contribute to greater coastal erosion through scouring and other activities as a result of them being hard surfaces on the top edge of an area that used to dissipate a lot of the wave energy.’’
If we want to keep salt marsh, we have to ‘‘think a little bit differently’’ about where we allow it to grow, he says.
Many coastal wetlands around Aotearoa are of cultural significance to iwi.
Ngāti Apa ki te Rā Tō is one of the iwi in Te Tau Ihu (top of the South Island) that has joined the Core and Restore pilot.
Aaron Hemi, the iwi’s cultural adviser, , says wetlands in the region are integral to the survival of the iwi’s ancestors, being places where they gathered and harvested food (mahinga kai), and resources like flax.
Matauranga Māori (Māori knowledge), including when and how to gather food and how flora and fauna interact, is at risk of being lost, he says.
It was hoped more ancestral matauranga Māori could be gained through the project.
Ecologist Jen Skilton, taiao (environmental) adviser to the iwi, says the estuarine environment in areas like Waimea Inlet includes flounder and mako shark, inanga (whitebait), kōkopu fish, and kōura (crayfish).
The iwi was drawn to the pilot’s kotahitanga approach of all working together to protect the environment for future generations, she says.
Hemi says such initiatives will hopefully inspire the younger generation to keep pushing the kaupapa forward, especially in areas of cultural significance.
Environmentalists say a potential blue carbon market could provide incentives for landowners to allow their marginal coastal land to return to wetlands.
Non-governmental organisation The Nature Conservancy (TNC) initiated a study last year to explore the possibility of a voluntary blue carbon credit market to finance large-scale coastal wetland restoration activities in New Zealand.
People who bought credits to help fund the restoration could use the credits to offset their emissions.
The study identified ‘‘a real opportunity’’ for blue carbon restoration projects in tidal salt marsh in Aotearoa, but said seagrass required further research.
TNC said it was in the process of identifying potential pilot blue carbon project sites to provide more detailed feasibility assessments, and demonstrate the generation and sale of credits.