Phytoplankton as Bio-Indicators of Water Quality of Lake Mboandong, Cameroon

Water quality and phytoplankton community structure of a tropical lake in Cameroon (Lake Mboandong) were evaluated using phytoplankton and environmental factors. Water samples were collected from 4 sampling sites, in January (dry season) and August (rainy season) in 2024 at the top 10 cm and analysed for physicochemical parameters. Algal identification was done with the light microscope at different magnifications, using relevant identification manuals. Results of the physicochemical characteristics of this study showed that the lake’s water was poorly oxygenated in the dry (2.35 mg/l) than the rainy season (3.78 mg/l), lower temperatures in the rainy (18.38˚C ± 0.52˚C) than dry season (19.04˚C ± 0.44˚C). Water pH was neutral to slightly basic, 7.49 ± 0.28 and 8.66 ± 0.07 in the rainy and dry seasons respectively. Higher turbidity occurred during the rainy season (10.93 ± 3.82 NTU) than in the dry season 6.56 ± 0.44 NTU. Nitrates were higher in the rainy (1.92 ± 0.99 mg/l) than in the dry season (0.52 ± 0.2 mg/l). Orthophosphate was rather higher in dry (3.08 ± 1.87 mg/l) than rainy season (1.53 ± 0.5 mg/l). A total of 77 phytoplankton were identified from 7 divisions. Bacillariophyta (18 taxa), Chlorophyta (23 taxa) and Cyanophyta (11 taxa) were the major groups. Total dry season abundance (7600 cells/L) was higher than that of the rainy season (3586 cells/L). Shannon-Weiner diversity was higher during the rainy (3.41) than during the dry season (2.51). Cyanobacteria contributed the largest (56.31% and 28.13%) in dry and rainy seasons respectively, mainly dominated by Microcystis aeruginosa and Synechococcus sp. Chlorella sp, Tetraedron caudatum, Selenastrum sp and Pediastrum duplex were common chlorophytes while Aulocoseira granulata and Cocconeis pediculus were common diatoms. The lake is a mildly polluted but productive lacustrine ecosystem that supports high phytoplankton diversity. The primary source of the pollution is the entry of inorganic and organic wastes from surrounding farmlands around the lake, as well as possible excessive nutrient levels due to the lake’s geological background.