Impact de l’exploitation du sable fluvio-lagunaire sur la qualité physico-chimique de l’eau des écosystèmes aquatiques du sud-Bénin

Abstract

Impact of fluvio-lagoon sand exploitation on the physico-chemical quality of water in aquatic ecosystems in south-Benin Description of the subject. The study of the physico-chemical quality of water aims to understand the ecological risks that sand extraction activity can generate on the environment and its resources. Objectives. To assess the impact of river-lagoon sand extraction on the physico-chemical quality of aquatic ecosystems in southern Benin. Method. Data were collected monthly from December 2018 to November 2019 at 16 stations, comprising eight dredged stations and eight undredged stations (reference stations). Thirteen physico-chemical parameters were analyzed: nine (temperature, pH, transparency, depth, salinity, dissolved oxygen, electrical conductivity, Total Dissolved Solids, current velocity) in situ and four others (NO2-, NO3-, NH4+, PO43-) in the laboratory. The Kruskal-Wallis test, Correlation Matrix, Ascending Hierarchical Classification and Principal Component Analysis (PCA) were used for the analysis of the collected data. Results. The results made it possible firstly, to identify the effects of sand extraction activity on the physico-chemistry of water in aquatic ecosystems through the analysis of the stations and secondly, to separate these stations into two groups. The first group consists of undredged stations and the second group consists of dredged stations. Undredged stations have highly mineralized waters, also associated with nitrogen and phosphorus pollution, which could create an imbalance in aquatic fauna. On the other hand, the stations subject to the sand extraction activity have the characteristics of well-oxygenated water, a pH that tends towards basicity, and highly transparent and deep waters. The results of this study show that the waters of dredged environments are well oxygenated. This means that these environments could become very favorable over time for the appropriate development of aquatic species, as the waters gradually regain their stability and become rich in minerals and nutrients again. Conclusions. This study will allow researchers and technical services responsible for monitoring the environment to better understand the effects of sand extraction activity on the physico-chemical quality of water in hydrosystems, leading to better management of these environments.

Keywords

• aquatic ecology
• lagoons
• water pollution
• eutrophication
• environmental factor