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Wairau Lagoons walkway (Photo: Wikimedia Commons)
Wairau Lagoons walkway (Photo: Wikimedia Commons)

ScienceFebruary 15, 2023

The untapped potential of blue carbon

Wairau Lagoons walkway (Photo: Wikimedia Commons)
Wairau Lagoons walkway (Photo: Wikimedia Commons)

Don’t overlook New Zealand’s saltmarshes and their carbon-sequestering superpowers, writes Ellen Rykers.

This is an excerpt from our weekly environment newsletter Future Proof – sign up here.

When it comes to sucking carbon out of the atmosphere, we usually turn to tree planting. But there’s an often overlooked opportunity to diversify our carbon sequestration portfolio, and it has me channeling my inner Shrek: swamps. Tidal wetlands – mangroves, seagrass meadows and saltmarshes – come under the “blue carbon” umbrella, which refers to the carbon stored in oceans and coastal ecosystems. 

These muddy margins of our coastlines may not be glamorous, but they’re powerhouses when it comes to sequestering and storing carbon – in particular, stockpiling it in the soils beneath the vegetation. Blue carbon habitats can store several times more carbon than equivalent areas of forest. They also provide heaps of other benefits, says marine ecologist Anna Berthelsen, like protecting people and infrastructure from flooding, providing a home for plants and animals, and offering cultural opportunities.

Berthelsen, from the Cawthron Institute, is part of a team who investigated the feasibility of blue carbon credits – a scheme where the benefits from protecting and restoring tidal wetlands are sold to those wanting to offset an activity. “It’s very important to prioritise reducing gross emissions before going down the track of offsetting,” says Berthelsen. “But it’s a way to funnel funds towards removing emissions from the atmosphere, improving livelihoods and protecting nature.”

The idea goes like this: take a degraded wetland, and start taking actions to restore it – like returning tidal flows by removing drainage, or replanting. This restoration then leads to more carbon storage (as well as the aforementioned raft of other benefits) compared to the baseline scenario. The relative positive outcomes can then be sold as blue carbon credits that fund the restoration. 

Commissioned by The Nature Conservancy and led by Ekos, the investigation delved into the nitty-gritty detail of how such a blue carbon credit system might work in New Zealand, focusing on six study sites. While one seagrass site proved tricky to analyse, five saltmarshes showed promise. This is a type of soggy reed-land that’s regularly flooded with saltwater by the tides. 

In short: “There’s a real opportunity for tidal salt marsh restoration blue carbon projects,” says Berthelsen. The resulting report recommends a saltmarsh pilot project alongside a nationwide inventory of tidal wetland ecosystems with blue carbon potential. 

Recently, the emissions-reducing efficacy of voluntary forest carbon credits has come under scrutiny. Nonetheless, it’s clear we can’t afford to miss investing in our saltmarsh superheroes. Our climate-resilient future looks swampy, and I’m here for it.

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