Conservation of the African Great Lakes: A Limnological Perspective

The limnology of Lakes Malawi Tanganyika, and Victoria is discussed with the objective of examining how the physical, chemical, and biological properties of the lakes will determine the response of these ancient great lake ecosystems to human activities. Of the physical properties discussed, large dilution capacities and long flushing times can make the detection and removal of chemical pollutants in these lakes difficult. The outflows of all three lakes are small because of high evaporation losses, and as a result lake levels are responsive to climate changes that would alter evaporation:precipitation ratios. Increased nutrient input to these lakes will likely result in a decrease in the volume of oxygenated water and available fish habitat. Plankton community composition will also change, probably toward dominance by cyanobacteria. While the effects of eutrophication on fish production are difficult to predict, changes in plankton composition would almost certainly be accompanied by changes in fish community structure. Recent studies of water chemistry and plankton productivity in Lake Victoria provide evidence of possible eutrophication. Because land use has a diffuse but potentially large impact on these lakes, conservation strategies must take into account human activities within entire drainage basins. This requires cooperation between riparian countries and technological and financial input from the international community. An immediate need is the establishment of monitoring programs to determine the impact, real or potential, of human activities around the lakes.