Human Impacts on Biodiversity

The impacts of human activities on biodiversity can be broadly characterised as: 

• Water quality
• Water quantity
• Alien Invasive Species
• Land use change

The main human activities driving these impacts are:

• Agriculture
• Mining
• Industry
• Infrastructure development
• Urbanisation

These two aspects of human influence are discussed below, along with the preliminary assessment of ecological status of the Limpopo River basin.

Human Impacts on Biodiversity

Water quality

Water quality is known to play a prominent role in determining the distribution of aquatic organisms. According to UNDP-GEF 2008, changes in Total Dissolved Solids (TDS) can affect aquatic organisms at three levels:

• Impacts on and affects the adaptations of individual species.
• Impacts on community structure.
• Affects microbial and ecological processes such as metabolic rates and nutrient cycling processes.

Aquatic biota is also affected by the presence of heavy metals, Persistent Organic Pollutants (POPs) and other chemical pollutants. They may reduce biodiversity (species richness) and change species composition – even selectively eliminating less tolerant species.

Agricultural effluents and return-flows can be unnaturally high in nutrients, causing eutrophication.  This is manifest through an accelerated and unbalanced growth of aquatic plants, reducing the availability of oxygen in the water and destroying the natural balance between plant and aquatic animal life in the water body.

Water Quantity

Reduction in streamflow for irrigation and water supply results in an overall reduction in the availability of water in the downstream ecosystems.  As water is a fundamental building block of aquatic life, reduction in streamflow has a direct impact on the biodiversity resources, limiting growth in all organisms.

Furthermore, attention of season flows caused by flow regulation of storage dams can have a negative effect on aquatic and riparian ecosystems.  Seasonal fluctuations in water availability are often a fundamental part of the growth cycle of plants, particularly those adapted to living in the riparian zone and on the floodplains of a river the size of the Limpopo.

Alien invasive species

Alien invasive species often do not have natural enemies in the invaded region. They can however compete with indigenous species for space, nutrients and sunlight. Dense invasions of aquatic plants can alter the flow of rivers and streams, disrupting the aquatic ecosystem. Reduction of light penetration reaching the deep portions of the water systems, and changes in bank vegetation resulting in erosion, alter and affect the aquatic environment.

Invasion by alien species has important socio-economic consequences (UNDP-GEF 2008).

Land use change

One measure of the impact of human activities on the landscape is reflected in the Human Footprint Index, undertaken by SEDAC at Columbia University in the United States (Last of the Wild Data Version 2, 2005b), shown in the map below.  This analysis shows the direct impact of human activities on the WWF biomes, clearly illustrating the wide scale transformation of the western Limpopo River basin through urbanisation and agriculture.

Human Activities Resulting in Biodiversity Loss

Agriculture

Agriculture has a series of known impacts on biodiversity:

• Water quality from agricultural effluents (live stock and arable agriculture) can modify the nutrient cycle of aquatic and terrestrial ecosystems.
• Change of land cover, modifying hydrological and runoff regimes.
• Introduction of alien species into ecosystems that can out-compete indigenous species.
• Pesticides and insecticides can damage adjacent plant communities and the chemical composition of these substances can be toxic to biota.

Mining

Mining has a series of known impacts on biodiversity:

• Water quality can be negatively impacted by heavy metals and acid mine drainage, causing significant damage to ecosystems; poisoning fish and mammals through bio-accumulation.
• Water quantity can be reduced caused by draw-down of groundwater or streamflow reduction for operational mining and use in processing facilities.
• Land change from mining activities causes profound disturbance to the landscape. Excavations for extraction, waste rock and tailings ponds all modify the shape and hydrology of the landscape.

Industry

Industry has a series of known impacts on biodiversity:

• Water quality can be negatively impacted by industrial effluents, causing damage to ecosystems; poisoning fish and mammals through bio-accumulation.
• Some industrial activities use significant volumes of water, which can reduce streamflow.
• Land change from industrial activities causes disturbance to the landscape.

Infrastructure development

Infrastructure developments have a series of known impacts on biodiversity:

• Reduction or modification of streamflow from storage dams limits or changes the availability of water for ecosystems.
• Water quality can be negatively impacted, particularly in terms of temperature
• Furthermore, water quality can be negatively impacted by transportation networks - spills and surface accumulation of fuels and automotive pollution (Ashton et al. 2001).

Urbanisation

Urbanisation has a series of known impacts on biodiversity:

• Land cover change for urban developments, obviously means removal of elements of the landscape.
• Modification of hydrological regime can mean more or less water available for biodiversity due to the introduction of impervious surfaces
• Water quality degradation from sanitation and polluted run-off can impact biodiversity.

Ecological Status

A preliminary assessment of the ecological status of the sub-basins of the Limpopo River basin is shown in the map below. This subject is discussed in more depth in the Environmental Flows section of this chapter.