Abstract
Temporal changes in the pattern and distribution of tropical wetland vegetation in four small impoundments over a 28-year period were documented for a wetland ecosystem in the Olezoa drainage basin in Yaounde, Cameroon, West Africa. These impoundments were constructed along the Olezoa stream for the purpose of aquaculture and ranged in size from 1.4 to 3.0 ha, had depths between 200 to 400 cm, and were devoid of vegetation. Evaluation of the impoundments and the surrounding catchment was accomplished using low altitude aerial photographs for the years 1964, 1974, and 1986 and field surveys for the periods 1985 through 1992. The results reveal a progressive decline in open water surface area of the impoundments ranging from 70 to 100% due to plant colonization and expansion. Measured impoundment depths along profiles show more than 50% reduction from original depths of 300–400 cm to less than 150–200 cm in 1992. We suggest that vegetation colonization and expansion in the impoundments is a function of the reduction of water depth due to siltation accompanying increasing urbanization. During the period of evaluation, urbanization in the surrounding catchment tripled. Siltation in the impoundments resulted mainly from the accumulation of soil eroded from the upland accompanying devegetation and construction activities. The shallowing of the impoundments by siltation provided a favorable water-depth regime and substrate for colonization by aquatic and emergent wetland vegetation. Continued shallowing resulted in development of vegetation zones along a water-depth gradient, and the migration of these zones toward the interior of the impoundments. The history of degradation of the catchment area and siltation of the impoundments is thus recorded by temporal changes in vegetation.
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Atekwana, E.A., Agendia, P.L., Atekwana, E.A. et al. Wetland vegetation colonization and expansion in small impoundments in Yaounde, Cameroon, West Africa. Wetlands 15, 354–364 (1995). https://doi.org/10.1007/BF03160890
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DOI: https://doi.org/10.1007/BF03160890