Conditions and Resource Factors Associated With the Spatio-Temporal Variability of Phytoplankton Community Composition and Abundance in the Tropical Meromictic Lake Bosomtwe (Ghana, West Africa)

Factors affecting phytoplankton community composition and abundance in Lake Bosomtwe (Ghana)

Abstract

Phytoplankton community abundance and composition of Lake Bosomtwe (Ghana), West Africa, were investigated on spatio-temporal scales for two years from water samples obtained from a central index station and 12 other stations to determine their annual, seasonal, and spatial signature and to assess environmental conditions and resource factors which affect their natural variability. In the laboratory, phytoplankton were identified, counted, and analyzed using an inverted microscope. Our study indicates seven phytoplankton groups with abundance dominated by the cyanobacteria composing at least 86% of it at all sampling times during the study. Mean cell abundance of 59958±31041 (n=51; CV=62.74%) for temporal studies and 16531±8734 (n=26; CV=52.84%) for spatial studies are consistent with other studies. Seasonally, mixed layer depth, euphotic depth, ratio of euphotic to mixed layer depths, water transparency, light intensity in mixed layer, extinction coefficient, surface temperature, total phosphorus, total nitrogen, ratio of total nitrogen to total phosphorus varied significantly (p˂0.05) with high variabilities. Phytoplankton abundance showed a clear seasonality associated with the mixing and stratification regime with significant differences (p˂0.05) occurring during the temporal study specifically between the restratifying period and the stratified and mixing periods respectively but not between the mixing and stratified periods. Variabilities of the meteorological factors showed no significant relationship with the abundance. Also, of the physicochemical and biological parameters, only variabilities in the ratio of euphotic to mixed layer depths (r²=7.60%; n=51), light intensity in the mixed layer (r²=9.31%; n=51), total phosphorus concentration (r²=14.41%; n=43) and the mixed layer depth (r²=9.31%; n=51) had a significant but weak relationship with the variabilities in the phytoplankton cell abundance at p˂0.05. Our study indicates that the spatio-temporal variability of the phytoplankton abundance of Lake Bosomtwe is mostly affected by the variability in a mixture of hydrographic and nutrient factors.