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Globally, peatlands cover just 3% of the world’s landmass but store twice as much carbon as all the world’s forests, according to the UN. And it turns out that New Zealand has some of the world’s deepest peat deposits.
Earth scientist Assoc Prof David Campbell, of the University of Waikato, who has studied peatland-atmosphere interactions for more than 20 years, says those deposits can reach depths of 10m to 14m.
Unassuming, ancient and fed solely by rainwater; peatlands are at the more extreme end of the wetland spectrum. Here species such as wire rush, Sphagnum mosses and cushion plants dominate. In this sodden anaerobic and nutrient poor environment, some plant species turn to devouring insects to supplement their diet. Importantly for climate change, partially decomposed plant matter steadily accumulates in peatlands over time, effectively sequestering carbon.
Research recently published in Nature Sustainability underlines the point.
It found that soil carbon represents 25% of the potential of natural climate solutions (total potential, 23.8 Gt of CO2e per year), of which 40% is protection of existing soil carbon and 60% is rebuilding depleted stocks. Soil carbon comprises 9% of the mitigation potential of forests, 72% for wetlands and 47% for agriculture and grasslands.
Intact and healthy peatlands take up CO2 and emit methane to the atmosphere, but the carbon they store from CO2 creates a net cooling effect. Carbon equivalent to about seven tonnes of CO2 per hectare each year gets locked up in the peat, Prof Campbell says.
‘‘They can’t compete with how quickly a young pine forest can take up carbon over short periods of time, but it’s sort of like the tortoise versus the hare," he says.
For example, the 11,000 to 14,000-year-old Kopuatai Bog in the Hauraki Plains is estimated to hold 2400 tonnes of carbon per hectare (T/carbon/ha), while a mature pine forest temporarily stores about 220 T/carbon/ha, Campbell says. "[Kopuatai Bog] is a national taonga, but so few people know about it."
Half of New Zealand’s peatlands are in the Waikato, where most have already been drained, according to the Waikato Regional Council. Southland is home to the South Island’s important stronghold for these wetlands. Although much is still intact there, a review published last year in the New Zealand Journal of Ecology showed 3452ha of peatland has been lost since 1990 and a further 3943ha is at risk.
Prof Campbell tells the story of Dunearn Peat Bog, in Southland, which was an "excellent example" of a raised peat bog ecosystem that was bought by the Department of Conservation in 2003. Before its purchase, a neighbouring landowner had dug very deep drains around and through the 60ha bog. As a result, the bog partially dried out, lost wetland species and invasive weeds established. Doc has tried to restore the peatland with mixed success.
"Restoring damaged peatland ecosystems is extremely challenging," Prof Campbell says, usually because the hydrology has been changed by land drainage and vegetation change, the peat has been degraded and nutrients added, and invasive weeds have taken hold.
It’s pleasing to see the dark peaty hue of Dunearn Peat Bog is still visible on Google Earth. However, the land is surrounded by green pasture that was also once peatland. The drainage of this ecosystem type represents a huge loss of carbon sequestering potential for New Zealand.
To compound the problem, Campbell says, when peatlands are drained, atmospheric oxygen can come into contact with the stored carbon in the peat deposits and react with it to form CO2. Turned from sequesterers to emitters, degraded peatlands will release CO2 to the atmosphere at annual rates of 12 tonnes to 40 tonnes of CO2 per hectare, he says, depending on the climate zone and how they are managed.
Less than 10% of New Zealand’s wetlands — that includes peatlands — remain since the arrival of Europeans. Conservation Minister Eugenie Sage says the Government plans to bring in rules to stop further loss of wetlands through a new National Policy Statement for Freshwater Management, with interim controls on land intensification until councils have plans in place through a new National Environmental Standard for Freshwater and Wastewater. Also coming to the aid of wetlands by 2028, the proposed National Policy Statement for Indigenous Biodiversity will require councils to identify and protect significant vegetation and habitat, as well as promote the restoration of degraded Significant Natural Areas.
Legislation won’t succeed without education. Prof Campbell talks to farmers in the Hauraki about the benefits of preserving wetlands in their region.
"If people don’t understand their freshwater ecosystems or resources then they can’t value them. I’ve got farmers now excited that Kopuatai wetland is still intact, when before it was ‘just a swamp down the back of the farm’ that they didn’t value. Like all things, education is really important. And that’s where I see a lot of my science coming in, to inform those value discussions."
For more information: www.wetlandtrust.org.nz