Cape Rivers of South Africa: Cape Rivers of South Africa

Size:
131,000 sq. km (50,000 sq. miles)

Habitat type:
Small Rivers

Geographic Location:
South Africa

Conservation Status:
Critical/Endangered

About The Area

The Cape Rivers and Streams begin in the Cape Fold Mountains, and are known for supporting a highly distinctive aquatic biota, demonstrating strong features of endemsim. The numerous rivers and streams in the ecoregion flow down toward the Indian and Atlantic Oceans, nourishing valleys along the way.

South Africa's Mother River, the Orange, flowing through raisin and date lands near the little Kalahari town of Kakamas, Republic of South Africa.

http://wwf.panda.org/about_our_earth/ecoregions/cape_rivers_streams.cfm

The range lies within one of the world's six "floral kingdoms" - Fynbos, where thousands of different plants grow in a small area. As the plants in the fynbos decompose, they release chemicals that then render the waters of the Cape Fold ecoregion acidic, staining the water to a dark hue.

An essential function of these rivers is to provide nutrient-laden sediments which are crucial for the existence of coastal ecosystems and for floodplain agriculture.

http://www.ngo.grida.no/soesa/nsoer/indicatr/fig3_12.htm

Human Benefits

Among the goods and services provided by rivers are habitats for many plants and animals, which include many economically important species - fish like bass and trout (even though these are non-indigenous and their presence creates ecological problems of their own); plants such as reeds (Typha), waterblommetjies, arum lilies and some medicinal plants; and sand and cobblestones used in construction and landscaping.

Historical Overview and Current Conditions

Certain researchers suggest that the semi-arid, South African river systems have been significantly altered from their original state and that in contemporary times they only support minor vestiges of their previous flora and provide just a mere fraction of their services when compared with their historical state. One approach to assessing this claim as well as record the long-term cultural and environmental impacts on the ﬂuvial environments of South Africa is through the use of historical photographs (Figure 1).

O'Keefe, J H. "A report of the Committee for Nature Conservation Research National Programme For Ecosystem Research." report of the Committee for Nature Conservation Research National Programme For Ecosystem Research. (1986): n. page. Print.

These photographic records demonstrate that there was a notable increase in the cover of riparian vegetation in the majority of all river systems in the study area in both the channel bed and adjacent ﬂoodplain ﬂuvial land forms (Table 1).

There was also a signiﬁcant increase in riparian vegetation cover in the perennial rivers albeit a few minor exceptions. Vegetation cover that has increased signiﬁcantly were usually associated with a narrowing of the river channel (Figure 2).

At certain sites the increase in riparian vegetation was because of a significant increase in the abundant arrival of invasive alien species which were commonly associated with the highly disturbed environments immediately below major dam walls such as the Clanwilliam Dam or Bulshoek Dam on the Olifants River (Figure 3).

The main trend observed in the repeat photograph pairs of the study area has indicated an increase in riparian vegetation over the course of the 20th century. Researchers interpret these findings in terms of four major environmental and cultural influences on river system process which vary in their degree of value for perennial rivers, major ephemeral rivers and minor tributaries and drainage lines:

reduced large-scale flood events due to climate change since the end of the Little Ice Age (LIA);

the damming and regulation of perennial rivers;

land use history particularly a decrease in herbivory during the second half of the 20th century;

increased CO2 fertilization and consequent woody thickening.

While there exists natural causes behind this increase in Riparian vegetation, humans have without a doubt contributed. This is potentially detrimental as an increase in alien plant and animal life are associated with this change, one of the many looming threats towards the Cape rivers of South Africa.

Human Impact and Threats

Water is in great demand in this dry ecoregion, with both urban and agricultural uses competing with the needs of the unique aquatic fauna, causing significant pollution along the way.

Many of South Africa's rivers suffer from habitat loss due to canalization. This is most evident in the densely populated urban areas such as Cape Town. The Big and Little Lotus rivers there, which are largely artificial, are canalized along most of their reaches. Straightening and deepening of channels also occur as a result of invasive alien plants. This has reduced the availability of habitat for aquatic life. The river’s ability to attenuate floods and decompose pollutants is also reduced by canalization.

article.wn.com

The construction of dams and interbasin water transfers alter the natural flow regime and block species movements.

http://www.dwa.gov.za/iwqs/rhp/state_of_rivers/state_of_umngeni_02/resource_units.html

Introduced species, particularly North American gamefishes such as Largemouth bass(Micropterus salmoides) and Smallmouth bass (M. dolomieu) have heavily impacted indigenous species.Other Invasive alien fish such as barbel, carp, tilapia are widespread in the lower reaches of nearly all of Cape Town’s rivers and these species compete with the indigenous Cape galaxias and Cape kurper for food and habitat. This has reduced the numbers and distribution of indigenous fish. A variety of alien aquatic weeds (water hyacinth, water lettuce, azolla, parrot’s feather) have also arrived in many of Cape Town’s rivers, particularly the Black, Lotus, Sand and Eerste/Kuils rivers.

Of the 19 indigenous fish in the fynbos system, 16 are endemic, and 15 are already highly threatened because of loss of habitat; the building of dams and weirs; channel modification through bulldozing; and the presence of invasive alien vegetation.

The overall state of these rivers are bad. Only a few of the upper reaches of the rivers in the greater Cape Town area are still in a natural or good ecological state. Development in the lowland areas has modified the rivers, resulting in their poor ecological state. Significant stretches of most rivers have been canalized have poor water quality, and modified flows.The ecological functioning and delivery of goods and services by these rivers have been severely reduced. Many rivers require rehabilitation.

dwa.gov.za

Protected Areas

The protected areas of South Africa are heavily concentrated upon terrestrial ecosystems. The is a overall ignorance and lack of understanding as to what benefits freshwater ecosystems and how to manage them. Over 90% of the Cape rivers fall outside of protected areas, half of the remaining rivers form boundaries, and only 5% fall under protected areas. Very few rivers are fully contained in a protected area.

www.csir.co.za

Percentage of Protection Level in Each Category:

Not Protected (0%)
Hardly Protected (<5%)
Poorly Protected (5-50%)
Moderately Protected (50-100%)
Well Protected ( ≥100%)

Only half of the rivers in the protected areas are in positive condition, but this is notably better than than the condition outside of the protected areas. These findings demonstrate the effectiveness of proper land management.

www.csir.co.za

Projections and Troubleshooting

If mismanagement of this ecosystem continues, a detrimental loss of fauna will be observed. The continuation of damming within this ecosystem will cause downstream changes in fauna and alteration of natural flow regimes according to supply needs, along with the interference with fish migrations. The consequences of organic and mineral pollution not only present danger to aquatic life, but also endanger the health of its human inhabitants. Introductions and dispersal of exotic fish and plant species will cause a reduction in habitat integrity that will further destabilize the ecosystem. Future increases in the human population can only lead to increased industrialization and urbanization, and the exploitation of marginal agricultural land, with concomitant increases in water extraction, mineralization and organic pollution.

In order to prevent these losses, certain precautions could be taken, especially to combat the infestation of alien species, modification of flows, and canalization of rivers.

Management Actions for Infestation of Alien Species:

Clear alien vegetation along and in the rivers and maintain these cleared areas.
Maintain green belts/buffers along the river corridors and
re-introduce indigenous riparian vegetation to act as a buffer between the river and surrounding areas.
Remove invasive alien fish from rivers.

Management Actions for Modification of Flows:

Implement monitoring and control measures on existing water abstraction.
Discourage new abstractions from Cape Town’s rivers in summer; instead store winter water for use in summer.
Ensure environmental flow releases are made from dams.

Management Actions for River Canalization:

Restore the natural channel shape and reintroduce meanders in rivers. Discourage additional canalization.
Introduce indigenous riparian and instream vegetation to beautify the river and improve water quality.
Create habitat diversity (pool and riffle/runs) to provide refuge areas for aquatic life.
Restore substrate diversity (rocks, pebbles, gravel, sand, mud) to increase biotic diversity.

References

. "Cape Rivers & Streams." WWF. World Wildlife Fund. Web. 24 Nov 2012. <http://wwf.panda.org/about_our_earth/ecoregions/cape_rivers_streams.cfm>.

. "Ecological State of Cape Town's Rivers." Department of Water Affairs. Department of Water Affairs South Africa. Web. 24 Nov 2012. <http://www.dwaf.gov.za/iwqs/rhp/state_of_rivers/ct05/ct_eng05.pdf>.

Hoffman, M. Timm, and Richard Frederick Rohde. "Journal of the History of Biology." Journal of the History of Biology. 44.1 n. page. Print.

."New Freshwater Ecosystem Atlas." SANBI. SANBI. Web. 24 Nov 2012. <http://www.sanbi.org/news/new-freshwater-ecosystem-atlas-launched>.

Skukuza, . "How Well Do Statuary Protected Areas Conserve Main Rivers in South Africa." The Council for Scientific and Industrial Research. CSIR, 3 2006. Web. 25 Nov 2012. <www.csir.co.za>.

Cape Rivers of South Africa

Wednesday, November 21, 2012

Cape Rivers of South Africa

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