Changes in the phytoplankton of the developing Volta Lake
1970
BISWAS, S., Volta Lake Research Project, Akosombo
The phytoplankton of the developing Volta Lake consisted of more than twice the number of taxa found in the river system before the impoundment. Such an increase in taxonomic diversity was not uniform in all the classes as the green algae increased four times the euglenoids eight times and the blue-green algae more than twice. The flagellates barely increased while the diatoms decreased due to the disappearance of some of the taxa common in the tributaries. There was a greater abundance of phytoplankton in the lower reaches than In the upper ones. In general, classes of algae represented by a few taxa showed a high density of populatIOn. This was especially the case with the diatoms in the lower reaches and occasionally the flagellates in all parts of the lake. In the river the phytoplankton varied from a near absence to a high peak of short duration before the flood. Such extreme variations were not observed in the lake. The peak initially showed no definite seasonal pattern but later it settled to the dry season following the flood. In the lower reaches of the lake the dominant organisms changed from the blue-green algae to the diatoms and then again to the former. Quantitatively, however, there has been a considerable decline of bluegreen algae. Most of the organisms occurred vegetatively in all parts of the lake throughout the year. They were present in the uppper layers during the months of stratificatIOn. Periodic mixing distributed them throughout the depth, especially during the months of floods and wind-action.
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