Diversity

Physical and chemical factors The lakes of sub-Saharan Africa can be divided into two broad categories of low and high relief conditions. The low relief areas occur in sedimentary basins and upland plains that are below 600 m above sea level and are represented by catchments of Nile, Chari, Niger, Senegal, Volta, and Zaire. Few mountainous regions such as the Guinean highlands occur here. The south and east are classified as high with relief of above 1000 m, and two major faultlines running NE/SW from Ethiopia to Zimbabwe are a major feature. The Western and Eastern Rift Valleys form trenches of about 1000 m below the top of escarpments bearing remains of intense volcanic activity. Such trenches are ideal traps of freshwater that harbor most of the lakes.

Owing to chemical constituents, Lake Tanganyika is classified as a soda lake, and is sometimes more closely associated with the Indian Ocean when compared with other adjoining lakes. The shallowness of Lake Victoria makes it one of the most productive as it undergoes complete mixing owing to current movement initiated by wind and internal seiches. Horizontal currents are influenced by wind speed and density-based buoyancy, resulting in upwelling and recycling of nutrients to sustain the food web. In deeper lakes, there is almost permanent stratification except for localized upwelling that sometimes generates catastrophic consequences as witnessed in August-September 1999 in central Lake Malawi,

Figure 1 The two Rift Valleys of eastern Africa and their associated lakes.

Figure 1 The two Rift Valleys of eastern Africa and their associated lakes.

where thousands of fish died from chemically reduced anoxic gases such as CO2, CH4, and H2S. A similar episode was reported from around Nkhata-Bay in northern Malawi in 1937.

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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