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Role of Apatite Weathering in the Eutrophication of Lake Victoria

  • Josh Holtzman
  • John T. Lehman
Part of the Monographiae Biologicae book series (MOBI, volume 79)

Abstract

We investigated biogenic and geochemical constituents of a short sediment core obtained during 1992 from a nearshore region in northern Lake Victoria. Diatom stratigraphy reveals disappearance of Aulacoseira from near surface layers, consistent with neolimnological observation of the lake. X-ray fluorescence, dry combustion, and wet chemical methods were used to measure bulk composition, as well as C, N, H, non-apatite P, and biogenic Si. Organically-bound P has increased somewhat in the top 10 cm, but the main Total-P increase appears to have been caused by increased amounts of apatite weathered from carbonatite minerals that are abundant in the region. Increases in non-biogenic Si and Ti in the top 10 cm indicate increased importance of terrigenous inputs during the 20th Century. Our data are consistent with the explanation that modern changes in land use practices, coupled with rainfall and lake level changes, have accelerated erosion of phosphate rich mineral soils into the lake. Weathering of these phosphate rich minerals are probably the source of persistent and elevated offshore P concentrations in Lake Victoria and other historically P rich lakes in East Africa. The main removal mechanism for lake P is sedimentation and burial, resulting in a residence time for P of 25 years. Loss rates of P parallel those of biogenic Si, indicating that elevated P concentrations are partly a consequence of floristic changes, especially the loss of fast-sinking diatoms.

Keywords

Nile Perch East African Rift Terrigenous Input Lake Level Change African Great Lake 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media Dordrecht 1998

Authors and Affiliations

  • Josh Holtzman
    • 1
  • John T. Lehman
    • 1
  1. 1.Department of BiologyUniversity of Michigan Natural Science BuildingAnn ArborUSA

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