title: 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 high-resolution 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.
authors.affiliation: Large Lakes Observatory, University of Minnesota, 10 University Drive, Duluth, MN 55812, USA. dirk.verschuren@rug.ac.be
authors.forename: Dirk
authors.initials: D
authors.lastname: Verschuren
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Johnson
authors.forename: Hedy J
authors.initials: HJ
authors.lastname: Kling
authors.forename: David N
authors.initials: DN
authors.lastname: Edgington
authors.forename: Peter R
authors.initials: PR
authors.lastname: Leavitt
authors.forename: Erik T
authors.initials: ET
authors.lastname: Brown
authors.forename: Michael R
authors.initials: MR
authors.lastname: Talbot
authors.forename: Robert E
authors.initials: RE
authors.lastname: Hecky
mesh_terms: D000351:Africa, Eastern; D000383:Agriculture; D000693:Anaerobiosis; D000818:Animals; D005075:Biological Evolution; D023681:Cichlids / Q000502:physiology; D000458:Cyanobacteria / Q000502:physiology; D017377:Diatoms / Q000502:physiology; D017753:Ecosystem; D005068:Eutrophication; D005618:Fresh Water / Q000382:microbiology* / Q000469:parasitology*; D006802:Human Activities; D006801:Humans; D010100:Oxygen / Q000378:metabolism; D010163:Paleontology; D010839:Phytoplankton / Q000502:physiology; D011158:Population Growth
chemical_list: D010100:Oxygen