“Rewetting” wetlands to reduce greenhouse gas emissions: Will it work and is it feasible?
George Edwards discusses recent findings that suggest “rewetting” wetlands could drastically reduce anthropogenic greenhouse gas emissions and whether this is a feasible option that could be used around the world.
Researchers in China have proved that by ‘rewetting’ wetlands, we can greatly reduce greenhouse gas emissions. Since the last ice age, wetlands have accumulated carbon, which they are now releasing as many have dried up, likely due to human activities disrupting the water table. Junyu Zou at the Southern University of Science and Technology, Shenzhen, China, and his colleagues discovered that dried, degraded wetlands emit carbon dioxide and nitrogen, while entirely flooded wetlands emit large quantities of methane. By ensuring the water table is kept balanced – just under the surface – it may be possible to reduce the methane emissions, while also storing carbon instead of releasing it into the atmosphere.
By analysing 3,604 global data records on greenhouse gas emissions from wetlands, the researchers noted that carbon dioxide and methane emissions were kept to a minimum when the water table was near to the surface. They also discovered that by rewetting wetlands, the amount of carbon being captured and stored by these ecosystems will offset nearly all the methane they emit (i.e. the amount of carbon dioxide being removed from the atmosphere by some wetlands is equal to the amount of methane being released into the atmosphere by others, so perfectly balanced wetlands are almost carbon neutral).
Methane and carbon dioxide are two of the strongest greenhouse gases – gases that trap heat energy from the sun in our atmosphere, ultimately causing global warming and climate change. By reducing the amount of these gases emitted, we can stop further warming before it happens. Currently, the main way governments are mitigating the effects of climate change is by reforestation. Yet this research suggests that rewetting wetlands can result in a greater reduction in emissions than all forest restoration projects combined. By extrapolating the current data, Zou and his colleagues revealed that between now and 2100, degraded wetlands will likely emit 408 gigatons of carbon.
By extrapolating the current data, Zou and his colleagues revealed that between now and 2100, degraded wetlands will likely emit 408 gigatones of carbon
408 gigatons? That sounds like a lot, right? Well, let’s put this into perspective. One gigaton is equal to one million tons. A Volkswagen Beetle weighs one ton. Therefore, by rewetting 4 million square kilometres of wetlands, we can stop the weight of 408 million VW Beetles, in carbon, being emitted. Furthermore, the paper estimates that “a volume equivalent of 10 per cent of anthropogenic CO2 emissions could be reduced through wetland restoration”. If this method of mitigation is possible, we could greatly reduce the amount of greenhouse gases being emitted within the next 80 years, significantly slowing the rate of global warming.
The paper estimates that “a volume equivalent of 10 per cent of anthropogenic CO2 emissions could be reduced through wetland restoration”
All this sounds incredible and offers hope, yet one question remains to be answered: can this be done? Can we really “rewet” 4 million square kilometres of wetlands across the globe in time?
There are already several ongoing projects that aim to rewet wetlands and peatlands. The process of ‘rewetting’ involves several techniques to raise (or lower) the water table to that perfect ‘just below the surface’ level. These include blocking drainage ditches from the wetland using peat, rocks or dams, planting flood-resistant vegetation to slow water flow, blocking underground channels, building raised embankments to retain water and restoring inflows.
Wetlands International is a charity that works with communities and industries to restore peat and wetlands for climate mitigation, while ensuring sustainable land use. They aim to rewet 50 million hectares of peatlands by 2050 and currently have ongoing projects in Russia, Indonesia and Mongolia. They emphasise the importance of peatlands, as these areas have “sponge-like qualities [that] mean they release water gradually and so reduce the risks downstream of both floods and drought” (both of which cause greater emissions of greenhouse gases). An article in the Economist highlighted the work being carried out by Wetlands International and the World Wildlife Fund in Indonesia where they are rewetting peatlands to reduce wildfires and combat climate change while still providing commodities from these areas.
The Indonesian government itself established a peatland restoration agency after the fires of 2015 and estimated that in order to restore 2.5 million hectares of peatland, approximately US$5 billion would be needed. They are currently still finding it hard to gain enough funding to do so as companies are more interested in forest restoration, according to the Economist.
So yes, it is possible to rewet wetlands and reduce their effects on the global atmosphere, but it is clearly an expensive project that is hard to fund. Furthermore, the Indonesian project is only aiming to restore 2.5 million hectares of wetland, whereas Zou’s paper emphasises the need to restore 400 million hectares (equal to 4 million square kilometres or 749 million football fields!). Therefore, with the above estimations, it would cost around US$800 billion to restore it all!
Although the paper sparks hope for possible ways to mitigate the emissions of wetlands, it may not be possible to restore 4 million square kilometres of wetlands before 2100, let alone beforehand! Yet with enough funding and support from governments and industries, it will be possible to make a dent in this key mitigation tactic.
More information about Wetlands International is available on their website.