The impact of land use changes on watercourses is poorly documented in Cameroon. Therefore, this study examines the effects of agriculture and urbanization on water quality, the structure and functional organization of macroinvertebrates of streams in the coastal zone of Cameroon. Nine sampling stations including three per catchment area with different land occupations (agricultural, urban and forest) were selected. Benthic macroinvertebrates were sampled monthly from February to July 2018 and the physicochemical variables were measured simultaneously. The urban and agricultural streams showed highly polluted waters with high nutrient and suspended matter content, whereas the forest stream waters are moderately polluted. In addition, the hierarchical ascending classification indicated a proximity in water quality between the agricultural and forest streams for which the main physicochemical variables did not vary significantly. With regards to macroinvertebrates, the forest watercourse is characterized by the proliferation of pollution-sensitive taxa, high diversity indices and complex trophic structuring, indicating its good ecological status. In contrast the urban watercourse, heavily polluted is characterized by low diversity indices reflecting a simplification of the structure of stands dominated by the pollution-tolerant collector-gatherer stands. The majority of biological indices and functional feeding groups were not significantly different between the agricultural and forest streams, sug

The abundance dynamic of some freshwater invertebrates in relation with the abiotic factors of the medium was studied from March 2013 to March 2014 on the main streams of the Wouri and Sanaga basins. Individuals of Copepoda, Atyidae, Chironomidae and Physidae were collected, identified and counted. Samplings were carried out monthly; meanwhile measurements of the environmental variables were taken. Results of the physico-chemical analyses revealed that water of the Sanaga basin is globally well oxygenated (77% -92%) and faintly mineralized (14 -107 µS/cm), excepted in the stations receiving household pollutants. Inversely, in the Wouri basin, waters are hypoxic with high content of organic matters (27.79 ± 9.43 mg/L). During rainy season (June-September), there is a dilution-dispersion of the organic matter due to stormwaters. Concerning biological analyses, the families of Physidae and Chironomidae were more abundant in urban stations than in stations situated in suburban area, especially during low water level period, showing that they are well adapted to anthropogenic and organic pollutions. The hypoxic conditions of urban waterways do not favor the proliferation of sensitive taxa such as Atyidae and Copepoda. These taxa preferred well oxygenated waters with rapid flow, and are more abundant during rainy season in stations located in suburban area or which are less subjected to anthropogenic disturbances.

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In this study conducted in the coastal zone of Cameroon, biological indices and functional feeding groups of benthic macroinvertebrates were used to assess the health status of two urban streams. For a better diagnosis, two streams located in coastal forest zone were used as a reference. Benthic macroinvertebrates were sampled monthly over a 3-month period (from May to July 2017) in six urban stations and six forest stations. Measurements of the physicochemical variables were done simultaneously. Physicochemical analysis revealed that urban streams are strongly polluted with high content of decaying organic matters, while forest streams are slightly polluted as indicated by the Principal Component Analysis. Concerning benthic macroinvertebrates, urban streams are poorly diversified with the proliferation of taxa tolerant to water pollution and belonging to the functional feeding groups of collectorsgatherers. Inversely, forest streams are more diversified and dominated by sensitive taxa, most belonging to the functional feeding groups of predators and shredders. These marked differences between biological indices and feeding mode of benthic macroinvertebrates in forest and urban rivers confirm the reliability of benthic macroinvertebrates as good indicators of freshwater ecosystem in the coastal zone of Cameroon.

Le bouleversement des conditions de la vie aquatique dû à la construction des barrages sur les cours d’eau a conduit à des déséquilibres de plus en plus graves, menaçant même la survie de certaines espèces comme les poissons migrateurs. L’étude de la qualité des eaux et des peuplements planctoniques dans la zone d'emprise du barrage de Memve’ele a été menée dans le but d’apprécier des éventuels impacts liés à son aménagement. Pour cela des prélèvements saisonniers ont été effectués aux mois de janvier et juin 2016, sur quatre zones étalées de l'amont vers l’aval du barrage en cours d'aménagement. Les analyses physico-chimiques ont été réalisées suivant les méthodes standards. L’échantillonnage du plancton s’est fait suivant les techniques appropriées et les analyses de laboratoire ont permis l'identification et le dénombrement des espèces. Les résultats révèlent que dans le réservoir en cours de formation, la pollution organique est substantielle et serait due principalement à la décomposition des feuilles, brindilles, branches et troncs morts abattus durant la préparation du site à aménager. Cette charge en matière organique a conséquemment entrainé la prolifération du peuplement zooplanctonique, notamment des larves nauplius et des Rotifères Rotaria rotaria, R. neptunia, R. citrina et Euchlanis meneta. Ce début de perturbation est également marqué par la prolifération de quelques indicateurs phytoplanctoniques tels que les Cyanophycées à l’instar de Planktothrix rubescens, Oscillatoria sp., O. splendida, O. subtilissima, Lyngbya sp., Schizothrix sp., Gloeotrichia sp. et Nostoc piscinale ; de même que certains Diatomées tels que Frustulia sp., Neidium affine et Cyclotella sp. Il est recommandé de mettre en place un programme de suivi de la qualité des eaux afin de suivre l’évolution du réservoir et d’anticiper les risques de bloom algal. The disruption of the conditions of aquatic life due to the construction of dams on the rivers has led to increasingly serious imbalances, threatening the survival of certain species such as migratory fishes. The study of water quality and plankton communities in the area of influence of the Memve'ele dam was carried out in order to assess the possible impacts related to its construction. To this end, seasonal samples were taken in January and June 2016, in four areas spread out from upstream to downstream of the dam under construction. Physicochemical water quality analyzes were done following standard methods. Plankton sampling was done using appropriate techniques and laboratory analyzes allowed the identification and counting of species. Results revealed that in the reservoir being formed, the organic pollution is substantial and could be due mainly to the decomposition of dead leaves, twigs, branches and trunks felled during the preparation of the site under construction. This organic matter load subsequently led to the proliferation of the zooplankton community, in particular the nauplius larvae and some rotifers species such as Rotaria rotaria, R. neptunia, R. citrina and Euchlanis meneta. This early stage of disturbance is also marked by the proliferation of some phytoplankton indicators such as Cyanophyceae species like Planktothrix rubescens, Oscillatoria sp., O. splendida, O. subtilissima, Lyngbya sp., Schizothrix sp., Gloeotrichia sp. and Nostoc piscinale; as well as certain Diatoms such as Frustulia sp., Neidium affine and Cyclotella sp. It is recommended to set up a water quality monitoring program in order to follow the evolution of the dam and anticipate the risks of algal bloom.