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 pilotwas 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