Bio-ecology of epilithic diatoms in the Mfoundi River (Yaoundé, Cameroon): diversity, spatial distribution and influence of organic pollution
The Mfoundi River is used for the disposal of solid wastes and waste waters from domestic and industrial activities, which can alter its water quality and biodiversity. The aim of this study was to assess the structure of diatom communities in the Mfoundi River in relation to some physico-chemical variables, i.e., analyzing the changes in species composition and the dominance profile of the main species along a pollution gradient. The diversity metrics (species richness, Shannon’s diversity index, evenness) and the percent pollution tolerant valves (%PTV) were also tested to characterize the water quality and the response of diatoms to environmental enrichment in organic matter. The physico-chemical analyses of the waters revealed a gradient of increasing pollution from upstream to downstream of the river. The upper reach presented turbid waters with high levels of suspended solids. The middle and the lower reaches were highly contaminated with organic matters originating from domestic sewage and industrial effluents. A total of 237 epilithic diatom taxa, mostly cosmopolitan, belonging to 39 genera distributed among 25 families were inventoried. The development in the upper reach of the Mfoundi of taxa such as Gomphonema parvulum (Kützing) Kützing and varieties, Gomphonema gracile Ehrenberg, and Navicula radiosa Kützing reflected in particular the turbid waters of this section. The distribution of Nitzschia palea (Kützing) W. Smith, Navicula geoppertiana (Bleisch) Grunow, Navicula mutica Kützing, and Pinnularia subcapitata Gregory in the middle and lower reaches was closely related to the organic load and high degree of mineralisation of the waters. N. palea was the most abundant species at the stations Mf5 (66%) and Mf6 (53%), indicating a significant organic contamination of these sites under the effect of discharges from brewery and wine-making industries operating within their vicinity. The spatial variation of diversity metrics did not reflect the full extent of the alteration of water quality, but the analysis of the %PTV revealed that incremental inputs of nutrients and organic matter in the middle and lower reaches of the Mfoundi may be contributing to the start of the eutrophication process in these sectors. This study showed that epilithic diatoms are sensitive to the variations in water quality of the Mfoundi, and can be used as bioindicators of the health status of urban streams in Cameroon.