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South Africa’s wetlands play a key role in climate change mitigation and disaster risk reduction, writes Alanna Rebelo. Part of the answer to surviving climate change may be South Africa’s wetlands. South Africa’s wetlands play a key role in climate change mitigation and disaster risk reduction, writes Alanna Rebelo ahead of World Wetlands Day on 2 February.
If the word “wetland” conjures up images of stinking, water-filled wastelands, like Shrek’s swamp, or the Dead Marshes in the Lord of the Rings, we need to do some rebranding.
In South Africa, we define wetlands as areas that have water above or near the surface of the ground, at least periodically, and which supports plants which have adapted to this wet lifestyle.
One may think of De Hoop Vlei, a coastal lake in the southern Cape which formed when sand dunes blocked the course of the Sout River. Or the largest Estuarine system in Africa, St Lucia in KwaZulu-Natal, which boasts mangroves, swamps and pans, home to 526 bird species, 82 species of fish, as well as crocodiles and hippopotami.
We have inland pans, like Barberspan in the North West Province, which is a freshwater lake surrounded by grassland, important for migratory birds. We also have temporary wetlands, like those on the Cape Flats and at Betty’s Bay, which disappear in the summer, and reappear in winter, resurrecting many species from various stages of dormancy.
From floodplain wetlands to valley-bottom wetlands to high altitude wetland seeps, these are just some of our diverse wetlands types. Wetlands make up only 2.4% of South Africa’s surface area, and yet we have 791 different types of wetland ecosystems.
But wetlands are not only popular tourist attractions, important for biodiversity and critical for community livelihoods, they also play a key role in disaster risk reduction – both for floods and drought – as well as water purification and capturing and storing carbon to reduce atmospheric greenhouse gases.
However climate is changing, becoming increasingly uncertain, volatile and warmer. A global temperature rise of 2ºC is likely to translate to a 4ºC increase for South Africa. The consequence of this is predicted to be less rain for the west of South Africa, and potentially more intense floods in the east. At the same time national demand for water is increasing. The greatest water user in 2016 was agriculture, consuming 66% of the national water budget. A growing economy needs reliable, safe water supplies. Can wetlands provide an answer?
Healthy wetlands can function as shock absorbers in the landscape, as dense vegetation is able to buffer the force of floods, or coastal storms. There is evidence that mangroves may be effective in coastal protection from tropical storms, typhoons and even tsunamis, by providing a natural barrier as a result of their dense tangles of roots, trunks and leaves. The Philippines government has invested US$8m to replant degraded stretches of mangroves, particularly on the islands of Leyte and Samar. Certain types of inland wetlands behave much the same, by slowing the movement of water through the landscape as a result of their dense mass of above ground biomass. Wetlands are also able to store water during the wet season, and release it slowly during the dry season. In this way wetlands are able to provide some protection from droughts.
Some types of wetlands, particularly valley-bottom and floodplain wetlands, are known for their ability to accumulate sediment through slowing the movement of water through the landscape. This process also allows more time for microbes or the vegetation they live in to consume nitrates, phosphates and harmful bacteria, as well as for phosphates to bind to sediments. In so doing, wetlands are like the kidneys of the earth, producing cleaner, less sediment-laden water, which is much less expensive to treat.
The Voëlvlei Dam, one of the dams in the Western Cape Water Supply System, was costing R4.7m per year in 2006/7 for chemicals and to treat algal blooms. If the wetlands above this dam had been kept intact, these costs may have been largely avoided. Healthy wetlands above water supply dams may also help increase the lifespan of those dams, by decreasing their rate of siltation.
Wetlands are the planet’s most effective carbon sinks. Peatlands, wetlands that build up peat (partially decayed vegetation), store twice as much carbon as is present in all the forests of the world (180-450 Gt globally). Peat typically accumulates over thousands of years, yet peatlands cover only 3% of the earth’s land surface. This makes them the most space-efficient carbon storage in the world.
Healthy wetlands, whilst taking up carbon, may also release methane into the atmosphere. However, many of these wetlands still act as net greenhouse gas sinks. When peatlands are drained or mined for peat, they begin to dry out, releasing carbon back into the atmosphere. Another major threat when wetlands are drained, is peat fires, which are effectively fires that burn underground – sometimes for years. Peatlands drained by humans account for 5% of our global greenhouse gas emissions.
Risks to wetlands
Unfortunately, wetlands are also vulnerable to climate change. Changes in temperature, rainfall, sea level rise and extreme events can also push our wetlands to the brink and beyond, changing their nature and ability to perform valuable services for society.
There are also other threats to wetlands. According to the 2018 WWF Living Planet Report, wildlife populations in freshwater ecosystems have declined by 83% globally since 1970, and wetlands have lost 87% of their extent. In South Africa, 48% of wetland systems are critically endangered, and 17% threatened, according to the 2011 National Biodiversity Assessment. With the results of the 2018 National Biodiversity Assessment expected to be released this year, these numbers are predicted to have worsened.
Wetlands have also been dubbed ‘ecological infrastructure’, a type of green infrastructure that, similarly to built infrastructure, needs to be invested in and maintained if optimal service provision is required. With many of our wetland systems nationally in critical condition, we need to invest in restoring or rehabilitating these ecosystems, as an insurance against climate risk.
If safe and secure water sources are a priority in the face of drought, then it makes sense to focus investment in South Africa’s strategic Water Source Areas. These – areas make up only 8% of the land surface nationally, but produce 50% of our fresh water. If protection against flood damage is a priority, then wetlands upstream of cities, towns or important infrastructure should be the focus.
Our government has invested R826.8m in the rehabilitation of over 1 000 wetlands. The private sector has also invested money in green infrastructure, a prime example is for the international stone fruit market in the Breede River Valley, due to concerns over declining water quality and security. But these investments need to be upscaled if we are going to make a difference to the damage caused to the country’s wetlands. Wetland rehabilitation and restoration for climate change mitigation is a prime opportunity for socially responsible investments in the future.
– Dr Alanna Rebelo is a postdoctoral research fellow in the Department of Conservation Ecology and Entomology at Stellenbosch University. February 2 is World Wetlands Day.