The geochemistry of Lake Bosumtwi, a hydrologically closed basin in the humid zone of tropical Ghana

Autor: E. R. Blood, Leonard Robert Gardner, W. E. Sharp, Benjamin F. Turner
Rok vydání: 1996
Předmět:
Zdroj: Limnology and Oceanography. 41:1415-1424
ISSN: 1939-5590
0024-3590
DOI: 10.4319/lo.1996.41.7.1415
Popis: Lake Bosumtwi lies in an isolated, hydrologically closed basin formed by a meteor impact ∼1 x 10 6 yr ago. Comparison of lake-water samples taken in 1993 with one from 1934 shows a decrease in the concentrations of dissolved solutes, most likely owing to an estimated 13% increase in lake volume. A mass balance calculation that uses an estimate of the average chloride composition of the rainfall shows that the most recent overflow of the lake occurred within the last 3,000 yr. Evaluation of the sources and sinks of major solutes suggests that deposition of harmattan dust may be an important component of the influx of ions into the lake. Although the lake is homogeneous with respect to major ion composition, it is stratified into an upper oxygenated layer and a lower anoxic layer, and there is an abrupt change in the concentration profiles of pH, NH 4 + , PO 4 3- , NO 3 - , and Mn at a depth of 16 m. This chemical stratification is apparently caused by photosynthesis in the upper layer and respiration and reducing conditions below. The stable isotopic composition of the lake water is reasonably well simulated by a simple isotope balance model for the lake. The model is used to show that the δ 18 O composition of the lake is relatively insensitive to changes in the water balance, but is highly sensitive to relative humidity and the isotopic composition of atmospheric moisture.
Databáze: OpenAIRE
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