History and timing of human impact on Lake Victoria, East Africa

Abstract

Lake Victoria, the largest tropical lake in the world, suffers from severe eutrophication and the probable extinction of up to half of its 500+ species of endemic cichlid fishes. The continuing degradation of Lake Victoria's ecological functions has serious long-term consequences for the ecosystem services it provides, and may threaten social welfare in the countries bordering its shores. Evaluation of recent ecological changes in the context of aquatic food-web alterations, catchment disturbance and natural ecosystem variability has been hampered by the scarcity of historical monitoring data. Here, we present highresolution palaeolimnological data, which show that increases in phytoplankton production developed from the 1930s onwards, which parallels human-population growth and agricultural activity in the Lake Victoria drainage basin. Dominance of bloom-forming cyanobacteria since the late 1980s coincided with a relative decline in diatom growth, which can be attributed to the seasonal depletion of dissolved silica resulting from 50 years of enhanced diatom growth and burial. Eutrophication-induced loss of deep-water oxygen started in the early 1960s, and may have contributed to the 1980s collapse of indigenous fish stocks by eliminating suitable habitat for certain deep-water cichlids. Conservation of Lake Victoria as a functioning ecosystem is contingent upon large-scale implementation of improved land-use practices.

Primary production in a tropical large lake: The role of phytoplankton composition

“…However, the annual primary production in Lake Kivu was in the same range as that in lakes Tanganyika or Malawi and no statistical difference can be observed between the phytoplankton production of these lakes (Table 5). Severe eutrophication of Lake Victoria, resulting into the highest pelagic Chla biomass for the East African great lakes (Table 4), arose from an important increase of human-population and agricultural activity from the 1930s onwards in its drainage basin (Verschuren et al, 2002). Higher phytoplankton biomass is still observed in the littoral areas and in closed bays (see e.g.…”

Anthropogenic impacts on the contextual morphological diversification and adaptation of Nile tilapia (Oreochromis niloticus, L. 1758) in East Africa

“…5 management are the Great Lakes of Eastern Africa, which are vital for the rapidly increasing human population in the region, but are also biodiversity hotspots with a remarkable number of endemic fish species (LoweMcConnell 2003). Over the past six decades the resources have been impacted majorly by anthropogenic activities (Mugidde 1993;Ogutu-Ohwayo et al 1997;Verschuren et al 2002). One of the most affected fish species in the region is Nile tilapia, which has had a significant impact following translocation to various habitats including aquaculture.…”

Spatial optimization of carbon-stocking projects across Africa integrating stocking potential with co-benefits and feasibility

“…These all occur in the equatorial belt areas with high rainfall and warm temperatures, and thus high potential productivity, but have been subjected to considerable degradation [22][23][24][25] . In contrast, much of the Congolian rainforests, which also receive high rainfall, exhibited relatively low levels of C-stocking potential due to their comparatively low levels of degradation 24 , while the Sahel's low potential for C stocking could be attributed to its low rainfall.…”

“…It has seen a human population explosion since the 1930s due to improved accessibility and health conditions 22,37 , resulting in extensive deforestation and soil degradation 22,38 . Thus, while much of this region achieved top priority in terms of C-stocking potential alone, its high population density and intense agricultural productivity underlie substantial land values.…”