False Bay Nature Reserve  (the Strandfontein Sewage Works)

Site description

Centred on the False Bay Waste Water Works (the Strandfontein Sewage Works), the proclaimed False Bay Nature Reserve also includes Zeekoevlei and Rondevlei. It is situated on the Cape Flats between Muizenberg and Mitchell’s Plain, 20 km south of Cape Town. Like many wetlands around South Africa’s major cities, Strandfontein is almost entirely human-made. Before 1922, the only wetland habitats at the site were the minor and temporary Maccoavlei and Tamatievlei. A small sewage works was built in 1922, and additional water was channelled into the system from nearby Zeekoevlei. Over the years, the complex has been enlarged, and by 1976, the small waterbody known as Tamatievlei had been converted into 34 settling ponds covering more than 306 ha.

The system provides a range of semi-natural habitats, including deep and shallow open water, seasonal open ponds, canals with aquatic vegetation, beds of reeds, rushes and sedges, bare and vegetated shorelines and islands. Well-grassed banks separate the ponds. Several distinctive wetland plant communities occur, including perennial wetlands, reedbeds, and reed and sedge marsh. The perennial wetland is characterised by sparse aquatic vegetation, while Typha capensis and Phragmites australis dominate the reedbeds. The reed marsh consists of virtually monospecific stands of Phragmites australis, invaded in parts by Typha capensis.

The sewage works depend mainly on chemical treatment, and reasonably clean water is released into the ponds. It previously functioned entirely by algal decomposition, a process that requires a large number of shallow vleis. The algae and the copepods associated with them provided a rich food supply for many bird species. The rationale for maintaining the ponds is that should there be a failure of the chemical plant, the previous sedimentation method of sewage treatment could be temporarily utilised. The water levels in the pans can be manipulated. In summer, the south-easterly solid wind can cause water levels to drop, resulting in variability in the water condition.

The natural terrestrial strandveld surrounding the wetland consists of a scattered perennial overstorey of spinescent species, succulents and moderately tall evergreen thickets. Annuals are conspicuous in the open areas in spring. Two vegetation types occur in the IBA, both endemic to within the City of Cape Town boundaries. The dominant type is Cape Flats Dune Strandveld, which is Endangered, and the other is Cape Flats Sand Fynbos, which is Critically Endangered. This vegetation is heavily invaded in many areas by a woody overstorey of alien species, mainly Acacia cyclops and A. saligna. The area is now primarily surrounded by suburban development.

The natural waterbodies of Zeekoevlei and Rondevlei were historically fed by groundwater infiltrating from the north and west. Recent urbanisation has fed these two vleis primarily by urban storm-water run-off. This has resulted in eutrophication of the waterbodies and extensive reed growth. Measures taken to improve water quality in Zeekoevlei and Rondevlei have included a cut-off drain, limited dredging and annual draw-downs of the waterbodies, all of which have shown some success. In the past, Zeekoevlei was infested with water hyacinth Eichhornia crassipes, which has subsequently been exterminated.

Apart from the large natural waterbodies, numerous smaller seasonal wetlands exist in the False Bay Nature Reserve dune troughs. These temporary wetlands often support attractive communities of plants and amphibians.

Birds

Although the wetlands act as a network, most birds are concentrated at Strandfontein Sewage Works, where 168 species have been recorded. Of these, 76 are freshwater wetland species, and 18 are coastal species that visit the area to roost or breed. Breeding has been confirmed for 45 waterbird species. This high diversity of waterbirds is due to the wide range of wetland habitats present and the proximity of Strandfontein to the ocean, which permits freshwater and coastal species to exploit the system.

The abundance of waterbirds supported by Strandfontein has increased progressively since the 1950s, reaching an average of more than 23,200 individuals from 1980–1990. In extreme years, numbers have boosted to above 30,000. Threatened and near-threatened species found at the sewage works are Greater Flamingo Phoenicopterus roseus, Lesser Flamingo Phoeniconaias minor, Great White Pelican Pelecanus onocrotalus, African Marsh Harrier Circus ranivorus, African Black Oystercatcher Haematopus moquini, Cape Cormorant Phalacrocorax capensis, Caspian Tern Sterna caspia and Chestnut-banded Plover Charadrius pallidus. Strandfontein occasionally holds globally significant numbers of Black-necked Grebe Podiceps nigricollis, Southern Pochard Netta erythrophthalma, Cape Shoveler Anas smithii, Pied Avocet Recurvirostra avosetta, Hartlaub’s Gull Chroicocephalus hartlaubii and Kelp Gull Larus dominicanus. White-winged Tern Chlidonias leucopterus historically occurred in high numbers, but these have declined dramatically over the past few decades.

Recent data analysis has shown that some key species are in decline and may no longer meet the IBA threshold for a significant congregatory population. This trend is likely in response to changes in water level and quality at the sewage works, as many settling ponds have been decommissioned. A further possible local reason for the decline is the invasive water hyacinth, which is not susceptible to biological control due to the cold winds. This has resulted in certain ponds no longer suitable for birds requiring open water. Cormorant species have also experienced a decline at this site, as they have in other areas, and declining fish stocks may be responsible for this decrease.

The site holds a regular tern roost of some 3,000 birds when the water is low enough for islands to form in the shallow pans, including reasonably large numbers of Common Tern Sterna hirundo, Sandwich Tern Thalasseus sandvicensis and Swift Tern T. bergii. Strandfontein occasionally holds regionally uncommon species, such as Yellow-billed  Egretta intermedia. The surrounding alien Acacia vegetation and the remaining strandveld hold Cape Spurfowl Pternistis capensis and Cape Bulbul Pycnonotus capensis.

IBA trigger species

The African Black Oystercatcher, Lesser Flamingo, and Cape Cormorant are globally threatened species. Regionally threatened species include the greater flamingo, Great White Pelican, African Marsh Harrier, Lanner Falcon Falco biarmicus, Maccoa Duck Oxyura maca, and Caspian Tern. Common biome-restricted species in the IBA include Cape Spurfowl and Cape Bulbul.

Species that meet the 1% or more congregatory threshold include Black-necked Grebe (maximum 174 individuals), Cape Teal Anas capensis (450 individuals), Cape Shoveler (630 individuals), Pied Avocet (550 individuals), Kelp Gull (2 000 individuals), Hartlaub’s Gull (830 individuals), Swift Tern (160 individuals), Egyptian Goose Alopochen aegyptiaca, Black-winged Stilt Himantopus himantopus, Southern Pochard, White-breasted Cormorant Phalacrocorax lucidus, Greater Flamingo, Spur-winged Goose Plectropterus gambensis and Common Tern.

Other biodiversity

Flat caco Cacosternum platys, a Cape Peninsula endemic, and arum lily frog Hyperolius horstockii, a fynbos endemic, are both present at the site. Two reptiles of conservation concern, Cape sand snake Psammophis leightoni and Cape dwarf chameleon Bradypodion pumilum, both of which are Vulnerable, have been recorded in the IBA. The Endangered western leopard toad Amietophrynus pantherinus also occurs in the IBA, and its presence at the site is of conservation significance. Two endemic butterfly species, the Critically Endangered Barber’s ranger Kedestes barberae bunta, which is restricted to the Pelican Park section of the False Bay Nature Reserve, and the unique ranger Kedestes lenis lenis, an Endangered species endemic to the Cape Flats, are also found in the IBA.

Conservation issues

Threats

The City of Cape Town administers the False Bay Waste Water Works. As the size of the sewage works grew over the years and the diversity of aquatic habitats increased, there was a dramatic proliferation in the numbers and diversity of waterbirds exploiting the complex. In the 1950s, approximately 200 individuals comprising 12 species could be expected; in the 1990s, thousands and tens of thousands representing between 50 and 60 species were regularly counted at Strandfontein. Recent count data suggest a decrease in numbers for many of these species, possibly due to changes in the functioning of the sewage works. Lesser Flamingo numbers had decreased dramatically by the 1990s, although individuals are still seen each year. The decrease may be due to the introduction of tilapia to the treatment ponds. These fish have changed the ecological character of the pans, reducing the abundance of small aquatic invertebrates, the flamingos’ favoured food item. In 1986, there was a switch to chemically based sewage treatment in Cape Town. As a result, the ponds are only used to treat sewage in emergencies and do not support as many birds as they did when sewage regularly passed through the system.

Birds that breed at the nearby Rondevlei and Zeekoevlei nature reserves probably forage extensively at the sewage works. Potential decommissioning of the settling ponds at the sewage works represents a significant threat, as this could lead to decreased nutrient levels. Changes to the nutrient levels impact the invertebrate fauna, thus affecting the foraging habitat of the birds. There is an additional threat of pollutants running into the area from small-scale agricultural and industrial activities nearby and artificially enhancing nutrient levels. The effluent from the surrounding settlements is usually treated before entering the settling ponds but often contains more nutrients than natural systems do. This can have a positive or negative impact, depending on the time of year and the nutrient fluctuations in the settling ponds.

Variations in the water level due to the operations of the sewage works have significant consequences for certain species, preventing them from foraging at certain times and establishing breeding sites. The water of the sewage ponds needs to be maintained at a particular level to benefit waders and other species. The Cape Bird Club and City of Cape Town authorities have agreed with the sewage management team to allow the water level to fluctuate naturally in two pans: they are relatively complete in winter and dry out in summer. There is also a plan to increase the water flow should levels fall too low. Natural fluctuation has produced extensive sand banks in Pan P2, where many terns and gulls roost. In addition, research is in progress at Pan P1 to establish the relationship between water levels and nutrients. The knowledge gained can be applied to manipulate water levels to improve the coastal habitat.

Attention should be given to the fact that several species of conservation interest, such as Caspian Tern, have stopped breeding in the area or show irregular breeding patterns. Breeding failure or a low success rate in waterbirds has usually been attributed to changes in water level. Disturbance at nest sites and predation by species such as Great White Pelican may also play a role. The management plan should promote the development of suitable breeding sites, including creating islands in the pans and manipulating water levels to prevent existing breeding sites from being flooded. On the other hand, increased breeding activity by some waterbird species has been observed at Strandfontein in the past decade and is believed to be due to improved water quality in the pans.

Alien vegetation has invaded some of the settling ponds at the sewage works. This vegetation, particularly water hyacinth, forms a mat over the entire water surface, preventing waders and waterfowl species from utilising these areas. Beds of Typha capensis at the edge of some ponds cover the mud banks that waders use for foraging and breeding. This species and water hyacinth have been extensively cleared from certain areas to improve the coastal edge.

From 2012 to 2015, a significant residential development (> 3,000 units) was built along the eastern boundary of Zeekoevlei and Strandfontein. Although this may lead to increased disturbance of birds at these sites, there will also be opportunities to engage the local residents in environmental education activities. There are recreational pressures associated with fishing and birding in the area, but the level of disturbance is shallow and does not pose a significant threat to the birds. There is a good relationship with local angling clubs, and fishing is confined to a few pans where bird numbers are low.

Conservation action

This IBA already enjoys formal protection and sound management by the City of Cape Town. The site consists of three major components: Rondevlei, Zeekoevlei and the False Bay Waste Water Works (also known as Strandfontein Birding Area). In its entirety, it has been identified as the False Bay Nature Reserve. It is awaiting proclamation as a provincial nature reserve, which will continue to be managed by the City of Cape Town. The environmental resource department manages the Strandfontein Birding Area in collaboration with wastewater works management.

Current conservation actions focus on managing alien vegetation, both terrestrial and aquatic; improving visitor safety and infrastructure (a project on the southern and eastern shore of Zeekoevlei is in progress); monitoring biodiversity (including regular CWACs); environmental education; and allowing the public access to a beautiful natural area which in turn raises awareness of the local environment. These activities are conducted within the specifications of detailed annual operations plans, with well-resourced environmental management teams, each led by a section ranger. The site has recently been granted Ramsar status, and a formal announcement to this effect was made on World Wetlands Day in February 2015.

Situated near Cape Town, Strandfontein is an ideal, easily accessible environment for avitourism. Appropriate facilities to exploit this potential have been developed, and opportunities to improve them are constantly sought. The wetland’s proximity to the suburbs of the Cape Flats provides further incentive to create economic returns for the communities living close by. The False Bay Nature Reserve facilitates a skills development programme, which will be expanded with additional funding. Furthermore, Strandfontein could fulfil helpful educational and scientific functions. The accessibility of this artificial wetland and its range of habitats and associated plants and animals give it excellent potential for environmental education. The Cape Town Environmental Education Trust and False Bay Nature Reserve staff are already co-ordinating ecological education at this IBA. However, further funding would give them scope to expand their efforts.

BirdLife South Africa, the City of Cape Town and the Cape Bird Club have partnered to improve the entire site as a centre for skills development, environmental education, biodiversity conservation and avitourism. The partners have developed a funding proposal focusing on skills development and environmental education projects. At the same time, it addresses ecological threats affecting the site. It includes socio-economic development activities that help mitigate the threats and benefit local residential communities. An overall steering committee that includes all the relevant stakeholders meets quarterly to discuss issues affecting the site and plan future partnership initiatives.

Related webpages

https://www.capetown.gov.za/en/EnvironmentalResourceManagement/Pages/NatureReserve-FalseBay.aspx