Abstract

Leaching of soil nutrients is a major problem for the agricultural prospects of many parts of tropical Africa. These nutrients do not simply cease to exist but are ultimately transferred to either the oceans or internal continental basins. The rift valley lakes of Eastern Africa provide excellent traps for these nutrients. Preliminary work suggests that the sediments of Lake Malawi may be a good source of phosphorous - one of the major limiting nutrients in most African soils. This project will determine the amount, distribution, form, and origins of phosphate in Lake Malawi sediments; and assess its potential for use as a low-cost fertilizer. Researchers will use the evidence gained from Lake Malawi and lakes elsewhere to develop models for phosphate accumulation in lake environments, especially in rift settings. These models can then be used as exploration guides for other such deposits, both in the region and elsewhere.

Post-Project Summary

Using data from echo sounding, "grab and shallow core" sampling, and previous investigations, researchers constructed a summary map of sediment distribution in Lake Malawi. They determined the characteristics of the three forms of phosphate minerals found: fish-bone concentrates; vivianite concretions and crusts; and insular guano. Of these, only the fish bone detritus in the southeast arm of the lake was likely to be recoverable. Large-scale exploitation of phosphates was deemed economically unattractive. The potential of shallow lagoons for small-scale artisanal use was not explored. Although the project did not meet all its objectives, it generated a great deal of useful academic and practical information. For example, evidence of the patterns of lake level fluctuations over the last 1 000 to 2 000 years indicated that the lake was at a historical high and could be expected to be lower in years to come, with extremely important implications for the regional economy. Also, the project alerted the Geological Survey of Malawi to the significance of the lake as a resource and prompted them to carry out further work on it.

Recipient Institution(s)