NFEPA Atlas 5.3_20111025_FINAL.indd - Biodiversity GIS - SANBI

1.3.3 Destruction or degradation of natural habitat1.3.4 Invasive alien species1.3.5 Climate changeHabitat destruction or degradation includes direct impacts (such as bulldozing andplanting of crops in wetlands or river channels) and indirect impacts (such as clearingnatural vegetation in the surrounding catchment, resulting in increased sedimentloads and erosion). Wetland ecosystems have been particularly hard hit: in agriculturalareas they have been predominantly dammed or drained for cultivation, and in urbanareas they are frequently completely transformed by infrastructure development. Thewidespread destruction and modification of river banks is a major problem as thisreduces the filtering capacity that healthy buffers of natural vegetation provide anddestroys freshwater plant and animal habitat (see principle 4 in Section 1.2).Destruction of river banksand wetlands, for example by ploughingor building infrastructure, results inoften irreversible damage to freshwaterecosystems and their ability to provideecosystem services.Invasive alien plant species have a substantial impact on riverine habitat and wateryield, consuming an estimated 7% of South Africa’s total annual runoff. The Workingfor Water programme in South Africa has created considerable awareness of theproblems associated with invasive alien plant water use.Invasive alien plants impact on riverhabitat and water yield. Invasive alien fishsuch as bass and trout, often introducedfor aquaculture or recreational fishing,disrupt ecosystem functioning and arethe number one threat to indigenous fishspecies.Less awareness exists around the threats posed to freshwater ecosystems by invasivealien fish, such as trout, bass and carp. These species are often introduced to riversystems for aquaculture and recreational fishing. Even when invasive alien fish arenot directly introduced in rivers, they often escape from farm dams in which they arestocked (e.g. when the dam wall is breached in floods). Invasive alien fish now occurextensively in most large rivers in South Africa, and impact on indigenous freshwaterplants and animals through altering habitats, competing for resources and eatingindigenous plants and animals. Invasive alien fish present a grave threat to indigenousfish species and have led to local extinctions in some river systems. Invasive alien fishhave also been associated with loss of invertebrates such as dragonflies. Un-invadedstreams (often the smaller tributaries of large rivers) frequently serve as the lastremaining refuges for indigenous freshwater species. Preventing invasions of alienfish in un-invaded streams is crucial, as controlling or eradicating invasive alien fishis difficult and expensive. Weirs can be useful for preventing upstream invasions,although an assessment of the environmental impact of the weir to the entirefreshwater ecosystem should be done prior to construction.Predicted changes in rainfall and temperature will impact on water resources. Thesechanges are likely to have a disproportionately large impact on runoff and river flow(Schulze 2005), with implications for future planning and management of water resources,especially around extreme events such as droughts and floods. For example, keepingrivers and wetlands healthy will help to regulate flow and reduce the risk of flooding.Climate change is also likely to impact on freshwater species. Animals may need to moveto rivers at higher altitude with cooler stream temperatures, and barriers in the riverchannel (such as dams) could restrict such movement.Changes in rainfall and temperature as aresult of climate change are likely to havea large impact on river flows. Keepingfreshwater ecosystems healthy will help themadapt to these changes with least disruptionto ecosystem services.Roxanne KleinAlien vegetation Obstructing river flow Habitat destructionErnst SwartzErnst SwartzIntroduction - 6 -