The ecology and nitrogen - fixing capacity of freshwater blue-green algae in selected localities in Tanzania

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University of Dar es Salaam
In the vicinity of Dar es Salaan and near the town of Zanzibar, 23 taxes belonging to six families of the Cyanophyta were identified, In a survey of streams, ponds, lakes, and fields, many taxa were found to be ubiquitous. In an ecological study in a rice field, certain environmental parameter, Cyanophyta population characteristics, and in situ nitrogen-fixation rates were measured concurrently over time. Total filamentous algal ubunctance (measured using a direct microscopical method) reached a peak of 0.53 mm3cn-2 at the end of the principal rainy season. Forms of the genera Oscillatoria Lyngbya, Anabaena, and Nostoc were dominant. Nitrogen-fixation (measured using the acetylene reduction technique) occurred at I3,6 nmol C2H4 cm-2h-1 at the end of the principal rainy season and 1.1 nmol G2H4 cm- 2h-1 during the cool dry season. Controls indicated that the Cyanophyta were primarily responsible for the nitrogen-fixation. Soil moisture was the the key factor controlling seasonal variation in algal abundance. Rainfall and shading by rice and weeds were important through their effect on soil rnoisture. Tillage of the soil caused a major disturbance of legal growth. Seasonal variations in solar radiation, temperature, soil temperature, pH, cation exchange capacity, and exchangeable K+ were relatively unimportant. There was a very significant correlation tween heterocystous algal abundance and nitrogen-fixation. Forms of Aulosira and Cylindrospermum fixed nitrogen in situ at 161.2 and 4l.6 nmol C2H4 cm-2n-1, respectively, indicating their promising potential as biofertilzers. Blue-green algae, particularly Anabaena were found to be consistently associated with Utricularia inflexa. Epiphytic blue-green algae both inside the traps and on the outer surfaces of the plant fixed nitrogen in situ. The association showed a. nitrogen fixing capacity of 20'12 nmol C2114 g(dry wt.) 1-h-1. Recommendations are given concerning the development of free-living algae and the Utricularia -Cyanophyta association as bio fertilizers in agriculture in Tanzania.
Freshwater Blue-green algae, Freshwater biology, Research
Wagner, G. M. (1983) The ecology and nitrogen - fixing capacity of freshwater blue-green algae in selected localities in Tanzania, Masters dissertation, University of Dar es Salaam. Available at (