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Phytoplankton Dynamics of Mokolo and Mopa Ponds in Bertoua City (East-Cameroon)

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Document pages: 15 pages

Abstract: This study aims to improve the understanding of algal community’sdynamics in response to different environmental factors in two dam ponds(Mokolo and Mopa) in the city of Bertoua (East-Cameroon). Physicochemical andbiological analyzes were carried out monthly by direct sampling at the surfaceand using Van Dorn bottle at 1 m depth. The organisms were collected usingtransparent glass vials of about 500 ml and fixed with 2.5 ml of a lugol solution,then analyzed using the Utermôhl method. Physicochemical analyzes show lowtransparency (75 cm) of theponds despite their shallow depth (≤150 cm), high levels ofdissolved oxygen (>60 ), BOD5 (>30 mg L) and chlorophyll “a” (>30 μg L). These data made itpossible to categorize the Mokolo and Mopa ponds as hypereutrophic withnitrogen as the limiting factor for eutrophication. Biological data show quitediversified ponds with 138 species identified inMokolo Pond and strongly dominated by Diatoms with 2951 ind. representing 46 of the total abundance. In Mopa Pond, 147 species were identified, mainlyrepresented by Chlorophyceae with 3629 ind. representing 52 of the totalabundance. Azpeitia africana (Mokolo) and Eresmophaera gigas (Mopa) were the mostrepresented taxa during the study. This study will have deduced that thestructure and dynamics of algal communities are under the control of differentfactors or processes that interact simultaneously, namely ascending factors orbottom-up corresponding to nutrient resources and sunlight and descendingfactors or top-down that are exerted by grazing and active physiologicalsubstances produced by other algae that are known to influence phytoplankton.

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