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Home The River Basin People and the River Governance Resource Management
The Limpopo River Basin
 Introduction
Geography
Climate and Weather
Hydrology
Water Quality
Ecology and Biodiversity
 Ecology
 Aquatic Ecology
 Building Blocks
 Aquatic Habitats
 Life in Aquatic Ecosystems
Factors Affecting Ecosystems
 Environmental Flows
 Wetlands
 Biodiversity
 Millennium Ecosystem Assessment
Sub-basin Summaries
 References

 



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Factors Affecting Ecosystems  

 

There is currently no basin-scale assessment of threats to aquatic ecosystems available for the Limpopo River basin.  The following table was developed by UNDP-GEF (2008) for the Orange-Senqu River system.  While this summary was developed for a different river basin, the factors and impacts are transferable to the Limpopo River basin.

Factors affecting aquatic ecosystems.

Factor

Impact

Alien species

Pioneer alien species out-compete indigenous species for space, nutrients and sunlight

Dams, inter-basin transfers, hydro-electrical flow releases, irrigation and mining abstraction

Modified flow regime or hydrology

Pollution from mines and return flows from irrigation

Reduction in water quality, including nutrient build-up and salanisation

Reduced flood regime and modified seasonal flows

Geomorphologic modification of the river channel due to lower flows, resulting in less or no scoured

Riparian and in-stream vegetation is harmed and continues to deteriorate

Floating aquatic plants increase with reduced flow

Changes to the shape of the wetted perimeter of the river channel, with lower water levels causing banks to dry out, temporary exposure of unprotected banks and bank collapse

Enhanced benefit to pioneer reeds, such as the Common Reed (Phragmites australis), under reduced flow, with increased distribution and patch size, thereby accumulating sediments, blocking channels and resulting in large disturbances when washed out during large floods. These often form reed mats that cause blockages downstream and exacerbate the effect of floods.

Loss of indigenous trees and gallery forest in the riparian belt because of reduced floods (moisture), reduced seed dispersal, more frequent hot fires because of increase in reed beds and less cooling effect as previously moist riverbanks are drier

Increased agricultural encroachment into the riparian belt because of reduced flooding and waterlogged soils

Invasion by alien vegetation, notably Mesquite (Prosopis spp.), exacerbated by a loss of indigenous vegetation and disturbance (e.g., through fires and agricultural activities)

Changes in species composition and abundance as a result of fertilizers and salts draining into the river, with for example Common Reed (P. australis) and Wild Tamarisk (Tamarix usneoides) increasing and having a negative effect on safsaf willow, Kaapse wilger or Cape Willow (Salix mucronata).

Source: UNDP-GEF 2008

In addition to eutrophication, a significant threat to aquatic ecosystems in southern Africa (and elsewhere) lies in the invasive species Water Hyacinth (Eichhornia crassipes) and Water Fern (Azolla filiculoides).

 



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