Blesbokspruit
- General Information
- Land Uses
- Ecology
- Topography and Geology
- Hydrology and Geohydrology
- Climate
- Threats
- References
General Information
Blesbokspruit is situated (260 17’ S; 280 30’ E) in the Gauteng Province of South Africa, at an altitude of approximately 1 600m above mean sea level. It covers approximately 1858 ha (±60km2). The site is approximately 3km east of the town of Springs on the East Rand of Gauteng Province. The towns of Boksburg, Benoni and Brakpan lie in the northwest, with Nigel located south of the site.
In 1995, the status of the wetland was as follows:
Blesbokspruit is a permanently inundated reed-dominated (Typha & Phragmites) wetland, which is permanently flooded, due to artificial inputs of water (e.g. from mines and sewage treatment works). The reedbeds are probably supported by eutrophic water.
Upstream of the designated wetland, the Blesbokspruit has two main branches, which flow eastward through highly urbanized and mined areas. There are several small dams on these branches.
Downstream of the designated wetland, the Blesbokspruit stream flows within the confines of a natural channel. The Blesbokspruit joins the Suikerbosrand River downstream. At Vereeniging, the Suikerbosrand River flows into the Vaal River Barrage, which is an important source of potable water for the greater Gauteng area. The Blesbokspruit is thus a sub-catchment of the Vaal River catchment.
Land uses
The Blesbokspruit Ramsar site is the responsibility of the Department of Agriculture, Conservation and Environment. This department reports to the national Department of Environment Affairs and Tourism, which in turn reports to the Ramsar Convention on the status of all listed sites in South Africa.
Surrounding land comprises mainly mines and agricultural lands with ownership being largely private, which complicates management issues.
Natural: Marievale bird sanctuary
Agricultural: Agriculture e.g. maize, vegetable, lucerne, kikuyu (lawn grass), fodder, flowers. Water from the Blesbokspruit is used to irrigate these crops.
Industrial: Many gold mines in the vicinity discharge their polluted water into the Blesbokspruit wetlands.
There are several sewage works on the edge of the wetland.
Urban: Approximately 45% of the catchment is urbanized while the remaining land is utilized for agricultural, mining and industrial activities.
Blesbokspruit is approximately 3km east of the town of Springs on the East Rand of Gauteng Province. The towns of Boksburg, Benoni and Brakpan lie in the northwest, with Nigel located south of the site.
Recreational: The Marievale Bird Sanctuary, in the south of the designated site, was in 1995 approximately 1 000 ha and is about 7,4 km long. It attracts mainly birdwatchers and hikers.
Ecology
Increasing urbanization and industrialization in the central Gauteng reduce the number of sites available to the local fauna and flora. Open water habitat is limited to small deep-water pools.
Vegetation: The Blesbokspruit wetland predominately provides dense (Typha sp. and Phragmites sp.) reed habitat. These reedbeds exist mainly as large and small single species colonies with some mixed species clumps. Inundated sedges and grassland (marshy habitat) is a small component, which exists mainly during the summer rainfall periods. These portions occur as a narrow band on the outer edge of the wetland.
Natural plant communities adjacent to the Blesbokspruit are described as Highveld Grassland. These communities are however currently limited due to urbanization and surrounding land use practices, such as mining and agriculture. Trees are not a natural feature in the landscape.
Aquatic vegetation: The aquatic habitat consists mostly of Phragmites australis, bulrushes Typha latifolia and sedges, which cover 90% of the water surface. These wetlands cover an area approximately 85% of the Marievale Bird Sanctuary. The exotic South American water fern (Azolla filiculoides) has been introduced into this country and occurs in many wetlands, including the Blesbokspruit. Transfer of this species between wetlands probably occurs when portions of the plant, seeds or spores become attached to waterfowl. This plant occurs mainly in slow moving or stagnant portions of the wetland.
Terrestrial Vegetation: The Blesbokspruit is situated in the Cymbopogon-Themeda veld (Acocks veld type no 48). This veld type merges with the Bankenveld and is a spare, tufted sourveld. The remaining 15% is grassland, which is broadly classified as Bankenveld. A wide variety of flowering plants occur. A few of the more spectacular are the Orange River lily Crinum bulbispermum, plough breaker Erythrina zeyheri and Aloe ecklonis.
Birds: Blesbokspruit supports significant numbers of waterfowl, including up to 4 000 yellow-billed duck (Anas erythrorhyncha) and 1 000 spur-winged goose (Plectropterus gambensis) in the dry season, when levels are maintained artificially at a high level. The high-productivity water provides food for greater flamingo (Phoenicopterus rubber) and lesser flamingo (Phoeniconaias minor) which are South African Red Data Book Species. Other notable birds include avocet (Recurvirostra avosetta), purple heron (Ardea purpe rata), spoonbill (Platalea alba), glossy ibis (Plegadis falcinellus) and yellow-billed stork (Mycteria ibis). African marsh harrier (Circus ranivorus), which has been displaced from much of the veld, maintains a strong population here. There are at least three heron roosts with a total of over 3 500 birds.
Mammals: The Blesbokspruit supports a variety of fish, amphibians, reptiles, crustaceans and rodents. Spotted-necked otters (Lutra maculicollis), water mongoose (Atilax palidinosus) and many larger birds depend on these animals for their food. The reedbuck (Redunca arundinum) regarded as uncommon in South Africa, has also been recorded here.
Topography and Geology
The geology of the area is fairly simple with flat lying sedimentary rocks of Karoo and Transvaal age, overlying older formations of gold bearing Witwatersrand.
The Blesbokspruit flows in a southerly direction through the Grootvlei Mines (Pty) Ltd area into the Marievale Bird Sanctuary which is the mining area of Marievale Ltd. Gold has been exploited from the Witwatersrand reefs in the East Rand since the turn of the century, however in the area under discussion, these reefs do not crop out on the surface. The Black Reef Quartzite Formation overlies the Witwatersrand strata unconformably and is in turn overlain by Malmani dolomites, which form an important natural water reservoir, these two formations form a part of the Transvaal sequence.
Extensive erosion took place prior to the deposition of the Karoo sequence. The basal formation of this sequence, the Dwyka Diamictite Formation is a clay-rich rock containing rounded rock fragments (up to boulder size) and is the product of Carboniferous continental glaciation. Overlying the diamictite, and the most common rock types to be found in the area, are sandstones and shales of the Vryheid Formation. Associated with these strata are coal seams, which have been mined, adjacent to the Blesbokspruit in the Groot valley area. During the entire geological history of the area, the whole sequence of rock has been intruded by igneous rock (mainly dolerite). The pattern of the outcropping rock strata today reflects an inlier, where younger rock (Karoo) has been eroded along the course of the Blesbokspruit and the older rocks (Transvaal) can thus be seen adjacent to the spruit.
Soils: Analises of the soils indicate a high nitrogen value.
Hydrology and Geohydrology
The Blesbokspruit is a hydrologically important river in the Gauteng province since it drains a large area before joining the Suikerbosrand River that ultimately flows into the Vaal River. The topography of the immediate catchment is gradual, so increases in flow have resulted in a lateral expansion of the wetland (i.e. becoming broader). The natural hydrology of the stream has been altered by artificial inputs of eutrophic water; for instance, the dry season flow is dominated by the point source discharges. Water quality is generally poor and the water chemistry (high sulphate, phosphate, nitrite/nitrate and ammonia concentrations) is similar throughout the wetland.
Climate
Precipitation: The average annual rainfall is 670 mm recorded over a period of 31 years (Madden, 1987). Hailstorms are not uncommon during summer. Snow falls on rare occasions. One of the heaviest snowfalls was recorded in July 1964 when a depth of 200 mm was measured and the area was blanketed for three days.
Temperature: Temperatures vary from -10° C in winter to 35° C in summer. Frost occurs from April through to October. During the coldest months of June and July, ice can occur on the shallow open water.
Threats
The primary cause of the degradation of the Ramsar site is Grootvlei mine, which continues to discharge polluted water into the wetland. The impacts are manifested primarily in two ways. Firstly, water quality has deteriorated, resulting in a decline in the abundance and diversity of aquatic animal species, as well as loss of species at certain trophic levels. Secondly, the seasonal fluctuation in water levels in the wetland has been replaced by permanently flooded conditions. Being in a climatic region characterised by summer rainfall, the system originally displayed a natural regime of high summer flows and reduced water levels in winter. This dynamic fluctuation in water levels maintained habitat diversity and ecosystem productivity. The result of high stable water levels, together with large concentrations of nutrients derived from domestic and industrial discharges upstream of the wetland, is a severe Phragmites reed encroachment problem that has brought about a decline in habitat diversity. This loss of the dynamic habitat mosaic has induced a corresponding decline in diversity of birds and other species depending on the wetland for feeding, roosting and breeding sites.
References:
- Ref 1: Madden, D. (1987). Help comes to the endangered Pamamanian Tamarin. Journal of Natural Science of California State University Fresno 2: 10-11.
- Ref 2: SOUTH AFRICA Ramsar Site 343;(WI Site 1ZA004)
- Ref 3: Blesbokspruit South Africa – Department Environment and Fisheries