Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
About Tutorial Glossary Documents Images Maps Google Earth Please provide feedback! Click for details You are here: Home>The River Basin >Ecology & Biodiversity >Aquatic Ecology > The River Basin Factors Affecting Aquatic Ecosystems Introduction Geography Climate and Weather Hydrology Water Quality Ecology & Biodiversity Ecology Dams Aquatic Ecology Building Blocks The building of dams can negatively affect ecosystems. It can result in the inundation Aquatic Habitats of habitats of limited distribution. If the water flow is interrupted during the Life in Aquatic construction or filling of a dam, a biodiversity hotspot such as the Kunene River Ecosystems Factors Affecting Aquatic mouth could fall temporarily dry with potentially devastating long- term effects for its Explore the sub- basins of the fauna. Dams would also obstruct the movement of fish species which could result in Kunene River Ecosystems the loss of certain species, some of which may be endemic, for example the Kneria Environmental Flows Maydelli in the Kunene River basin. On the other hand dams can create new lake Wetlands habitats and can have other positive effects such an improved fishery potential or Biodiversity regulated flows. Watersheds References Factors Affecting Aquatic Ecosystems Abstraction of water The abstraction of water for water supply to settlements and for irrigation can also have a negative impact on the ecosystems with effects similar to those described above. The high demand of water for the arid parts of the Lower Kunene especially in Namibia needs to be balanced with the demands in the upper sections of the watershed Video Interviews about the integrated and transboundary in Angola. Water volumes (supply/ debit versus demand/ extraction) need to be management of the Kunene carefully managed to avoid negative effects on the ecosystems. River basin Explore the interactions of living organisms in aquatic environments Water is abstracted from the Kunene River to supply Northern Namibia. Source: GTZ 2006 ( click to enlarge ) Degradation of riparian vegetation send a general website comment report a specific comment about this page In general population densities are low to very low especially in the Lower Kunene basin. However, human activities in agriculture and pastoralism lead to the degradation of the riparian vegetation. This can have negative effects such as the reduction or fragmentation of habitats for wildlife in the floodplains of the Middle and Upper Kunene watershed, where population pressure is highest. Alien species A significant threat to aquatic ecosystems in southern Africa (and elsewhere) lies in the invasion of alien species. The most prominent example for problems with invasive species is the Nile Perch in Lake Victoria. After being introduced to the lake this species has out- competed most of the indigenous fish population and robbed the lake Examine how the hydrologic cycle moves water through and around the earth A significant threat to aquatic ecosystems in southern Africa (and elsewhere) lies in the invasion of alien species. The most prominent example for problems with invasive species is the Nile Perch in Lake Victoria. After being introduced to the lake this species has out- competed most of the indigenous fish population and robbed the lake of its formerly high fish diversity. Another well known invader is the water hyacinth (Eichhornia crassipes ) which has spread in most African fresh water habitats leading to clogged waterways, eutrophication and problems for hydropower schemes resulting in economical and ecological losses. The water hyacinth is for the moment absent from the Lower Kunene. Compared to other regions, Namibia has been relatively spared from invasive species. The integrity of forest ecosystems is relatively unscathed by the impact of evasive aliens with the exception of ephemeral river forests with severe infestation of Mesquite (Prosopis sp.) (Kohli et al 2008). Factors Affecting Aquatic Ecosystems Factor Impact Dams, interbasin transfers, hydro- electrical flow releases, Modified flow regime or hydrology irrigation and mining abstraction Alien species Pioneer alien species out- compete indigenous species for space, nutrients and sunlight 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. Degradation of riparian and inLoss of indigenous trees and gallery forest in the riparian belt stream because of reduced floods (moisture), reduced seed dispersal, more vegetation 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 Source: UNDP- GEF (2008) For more information refer to section Threats to Biodiversity . Next: Environmental Flows