Gallery forest species and water quality of the Okpara River in northern Benin

Abstract

This study aims to understandf the relationships between water quality, vegetation and human activity in the forest gallery of the Okpara River in northern Benin. Within this framework, floristic surveys and measurements of physicochemical parameters were carried out on 48 sites along the watercourse, located in 8 villages bordering the river. Sociodemographic surveys were also carried out among neighboring populations. The densities of Khaya senegalensis, Mitragyna inermis, Vitellaria paradoxa, Cola laurifolia and Isoberlinia doka of the wooded stratum and the recoveries of Andropogon gayanus, Cassia mimosoïdes, Panicum maximum, Andropogon tectorum, Hyptechis suaveolens and Aptechis suaveolens increased from upstream to downstream. The water can be considered as water of average quality according to the parameters measured. It emerged that the density of Berlinia grandiflora, Isoberlinia doka and Combretum glutinosum on one hand, and the recovery of Andropogon gayanus, Cassia mimosoïdes, Detarium microcarpa and Gynandropsis gynandra on other hand were particularly linked to the physicochemical parameters of water. There was a relative strong relationship between the two groups of parameters with the first canonical coefficient estimated at 0.75. The species richness of shrubs and herbaceous plants, water temperature, Biochemical Oxygen Demand for 5 days and, to a lesser extent, dissolved oxygen contributed to the relationship between the two groups of variables. The importance of human activities from upstream to downstream was also a factor that had a detrimental effect on water quality and on the composition of riparian flora. This information is important for a good sustainable management of these resources.

Keywords

• Okpara river
• Water quality
• Gallery forest
• Human activity
• Benin