Stellenbosch - South Africa's palmiet wetlands provide important ecosystem services to society, but are in such a critical state that if urgent action is not taken now "they may soon disappear right before our very eyes", according to Stellenbosch University research.
“It’s been reported that over 65 percent of South Africa’s wetlands and associated river systems have been damaged and 50 percent estimated to have been destroyed. If steps are not taken immediately to restore palmiet wetlands threatened with erosion, it is possible that these wetlands will be drained or lost by 2065,” wetland ecologist and postdoctoral researcher in the department of conservation ecology and entomology at Stellenbosch University Dr Alanna Rebelo said on Sunday.
Her research focused on the Theewaterskloof and Goukou wetlands in the Western Cape as well as the Kromme wetland in the Eastern Cape. Located in the Cape Floristic Region, one of the world’s biodiversity hotspots, these wetlands had a remarkably similar vegetation composition. Two of these palmiet wetlands were situated upstream of large municipal reservoirs providing water for Cape Town and Port Elizabeth, she said.
Rebelo measured their soil and water chemistry, vegetation community structure, and groundwater parameters to try to understand what they were like in terms of their biochemistry, and in particular what physical aspects drove the vegetation community structure.
She used a combination of aerial photograph analysis, remote-sensing and modelling techniques to map the current and historical distribution of wetlands and what remained of them, how their spatial distribution had changed over time, and what the main drivers of this change were. She also wanted to determine how wetlands function in providing ecosystem services.
Rebelo said of all ecosystems, wetlands were considered one of the richest in terms of services provided. “They attenuate floods, mitigate water pollution, retain sediment, provide clean water and food for local communities, and capture and store atmospheric carbon dioxide. They also have valuable peat-beds beneath them which, if degraded, will contribute to global warming.”
Rebelo said that despite this, the complexity of wetland ecology had resulted in them being the least studied. South Africa’s wetlands were not well understood and many were in decline.
“The ecosystem services palmiet wetlands provide could soon come to a halt. The remaining wetlands are threatened by a plethora of different problems such as being removed to make place for agriculture, gully or channel erosion, pollution from agricultural runoff like lime and fertilizers, invasion by alien vegetation, increasingly extreme flooding, and inappropriate fire regimes," she said.
“Bisecting roads also have a negatively impact on palmiet wetlands because they cause knick-points in wetland systems, often resulting in erosion, which eventually drains the wetland. Once this erosion begins, it is impossible for the system to recover without active rehabilitation, which is costly. This wetland drainage results in a shift in vegetation communities,” Rebelo said.
The value of palmiet wetlands in terms of water purification, among other ecosystem services, had been overlooked in favour of their potential for fertile soil for food provision. “As a result, many of these palmiet wetlands have been ploughed up for agriculture, either for orchards or grazing.”
She said it was unfortunate that landowners often believed that palmiet choked rivers and should be removed. “It is in ‘choking’ rivers that palmiet is able to provide many important ecosystem services to landowners, and to others further downstream. These include slowing the force of dangerous floods, thereby minimising infrastructural damage, allowing deposition of sediment which then would not accumulate in the dam, and in dispersing the movement of water, in doing so providing a filtration service and improving water quality.”
Rebelo said her findings highlighted not only the uniqueness and value of palmiet wetlands, but also their decline and made a case for their conservation and restoration. “It is hoped that the findings of my study will feed into conservation and restoration planning, and possibly policy, with real implications for the protection of ecosystems and biodiversity. The protection and restoration of our wetlands should be a national priority,” Rebelo said.