Rietvlei Wetland
Rietvlei Wetland Reserve, located near Cape Town, South Africa, is a vital ecological area recognized for its rich biodiversity and recreational opportunities. Spanning approximately 2,175 acres (880 hectares), the reserve is classified as a coastal freshwater wetland and is home to around 180 bird species, including pelicans, flamingos, and various migratory birds, making it a notable destination for birdwatchers. Established as a protected nature area in 1984 and later designated as a wetland reserve in 1993, Rietvlei is also facing environmental challenges, notably pollution and habitat degradation from human activity.
The wetland's diverse ecosystems feature permanent freshwater lakes, seasonal pans, and extensive reedbeds, primarily dominated by the reed Phragmites australis. Despite its ecological significance, Rietvlei has been impacted by invasive species and rising salinity levels due to climate change, which threaten its unique habitats. The reserve also plays a crucial role in filtering water, although recent pollution issues led to temporary closures for recreational activities. As development encroaches on the surrounding areas, Rietvlei Wetland remains an essential sanctuary for wildlife and a location for nature enthusiasts.
Rietvlei Wetland
- Category: Inland Aquatic Biomes.
- Geographic Location: Africa.
- Summary: A hot spot for biodiversity and a birder’s paradise, the Rietvlei Wetland Reserve offers a unique haven for nature and recreation in an otherwise developed region.
The Rietvlei Wetland Reserve is located in South Africa near the city of Cape Town and is part of the Table Bay Nature Reserve, spanning 2,175 acres (880 hectares). The wetland received its first official recognition in 1984, when the South African government proclaimed it a Nature Area. In 1993, the government officially declared the wetlands the Rietvlei Wetland Reserve, and now the area is identified as a Protected Natural Environment within South Africa. Future plans focus on the government declaring the wetlands area a Provincial Natural Reserve. The name Rietvlei originates in the Afrikaans language, with riet and vlei meaning reed and marsh.
Rietvlei is a wetland of approximately 1,638 acres (663 hectares) located on the floodplain of the Diep River. The wetland is characterized as a coastal freshwater wetland, but at times the salinity can rise as high as 13 parts per thousand as a result of evapotranspiration. (Seawater is generally 35 parts per thousand.)
The climate is moderate, ranging from a low of 47 degrees F (9 degrees C) during the region’s two coldest winter months of July and August, rising to as much as 78 degrees F (25 degrees C) during the summer months of January and February; there is a rainy season of May to September. Total annual rainfall is approximately 27 inches (686.2 millimeters).
The Wetlands
The wetland occupies the low-lying area between two barrier dune systems. The landward edge was formed during the last interglacial period, while the seaward edge is part of an older dune system. The reserve is elongated parallel to the coast for about 3 miles (5 kilometers) and is 328 feet (100 meters) wide. It drains into Milnerton Lagoon and finally into Table Bay.
The wetland is characterized by a permanent freshwater lake, shallow seasonally inundated pans, extensive reedbeds, true riverine habitat, and a tidal lagoon with salt marshes open to the sea. The dominant vegetation is the reed Phragmites australis. The site receives about 17 inches (432 millimeters) of rainfall per year, and the climate is defined as semiarid.
There are five distinct wetland plant communities: perennial wetland, reed-marsh, sedge-marsh, open pans, and sedge pans. The perennial wetland has little aquatic vegetation, but does include Ruppia, Potamogeton and Enteromorpha. Dominant in the reed-marsh is Phragmites; in the sedge-marsh, Bolboschoenus and Juncus prevail. In the open pans are macrophytes, mainly Limosella and Salicornia, and in the sedge pans are Bolboschoenus in summer, and Aponogeton and Spiloxene in winter.
Anecdotal reports state that the wetland was considerably deeper in the past. Increased siltation since the late 1800s has markedly reduced the depth of the Diep estuary. Salt intrusion due to sea-level rise, tied at least in part to global warming, also has affected the Rietvlei wetland. It has been predicted that with sea-level rise of 3 feet (1 meter) or more, the Rietvlei will effectively become salt water and be connected directly to the Milnerton Lagoon.
Wetlands provide the essential ecosystem service of filtering water for human use. Even though little direct water use in the area depends on the Rietvlei wetland, the health of the nearby lagoon is very much intertwined with surrounding wetlands. Invasive species are a problem for the functionality of the reserve. Specifically, Port Jackson willow (Acacia saligna), rooikrans (Acacia cyclops), and kikuyu grass (Pennisetum clandestinum) are a problem.
Biodiversity
The Rietvlei wetland is recognized as an Important Bird Area by BirdLife International, with up to 180 identified species, including pelicans, flamingos, ducks, coots, herons, plovers, weavers, and swallows. The wetland provides habitat for both residential and migratory birds.
The lagoon offers a nursery to several coastal fish, such as the harder and mullet. The Southern African Foundation for the Conservation of Coastal Birds (SANCCOB) manages a rehabilitation facility at Rietvlei. Although much of the surrounding region is becoming developed, the Rietvlei Wetland Reserve offers a sanctuary for such wildlife as the lesser flamingo (Phoenicopterus minor), and recreational activities.
Environmental and Conservation Issues
The most dramatic human modification to the wetlands occurred in 1974–76 when the entire northwest region was dredged to provide material for the construction of docks used for recreation purposes. To facilitate the dredging process, salt water was pumped into the marsh, creating the present-day permanent lake.
The most significant threat to the Rietvlei wetland in the 2020s was pollution. Rietvlei was closed for recreation in 2021 because of high levels of E. coli in the water, which poses a threat to human health. The area was reopened in 2022 although concerns about the water quality and sewage remained. Water sampling in 2024 revealed dangerously high levels of E. coli that far exceeded the safety threshold.
Bibliography
Carr, Andrew S., et al. “Molecular Fingerprinting of Wetland Organic Matter Using Pyrolysis-GC/MS: An Example From the Southern Cape Coastline of South Africa.” Journal of Paleolimnology 44, no. 4 (2010).
Daniels, Kailin. “Rietvlei Faces New Contamination Crisis With E. Coli Levels Far Above Safety Limits.” News 24, 19 Sep. 2024, www.news24.com/news24/community-newspaper/tygerburger/rietvlei-faces-new-contamination-crisis-with-e-coli-levels-far-above-safety-limits-20240919. Accessed 15 Nov. 2024.
Grindley, J. R. and S. Dudley. “Estuaries of the Cape: Part II: Synopses of Available Information on Individual Systems.” CSIR Research Report 427 (1988).
Hughes, P., et al. “The Possible Impacts of Sea-Level Rise on the Diep River/Rietvlei System, Cape Town.” South African Journal of Science 89, no. 10 (1993).
Human, Liezl. "City of Cape Town Dragging Its Heels on Rehabilitation on Rietvlei Wetlands, Claims Milnerton Aquatic Club." Daily Maverick, 3 Sept. 2021, www.dailymaverick.co.za/article/2021-09-30-city-of-cape-town-dragging-its-heels-on-rehabilitation-of-rietvlei-wetlands-claims-milnerton-aquatic-club/. Accessed 15 Nov. 2024.
Ntseku, Mthuthuzeli. "Rietvlei Water Body Closed Again over Water Quality and Health Concerns." IOL, 31 Dec. 2021, www.iol.co.za/capeargus/news/rietvlei-water-body-closed-again-over-water-quality-and-health-concerns-775cc48b-4434-4bb3-8ebb-377ccc8c2900. Accessed 15 Nov. 2024.