Augustin KOUAME N’guessan^1,, KOUAME Mathias Koffi^{1, 2}, Marius Tanoh KAMELAN¹, Valentin N’DOUBA¹

A study on some physical and chemical variables of water quality was conducted on North-western Ivory Coast. The objective was to assess the physico-chemical quality of Bagoue watershed subjected to artisanal and clandestine gold mining. Data were collected during four sampling campaigns at six stations from August 2018 to April 2019. Twelve physicochemical variables were measured in-situ and two (total mercury and total suspended solids) were measured in the laboratory. The principal component analysis was carried out in order to classify the watershed in an area. The Kruskall-wallis test was applied to determine spatial variation in physicochemical parameters. Spearman’s test assessed the level of correlation between physicochemical variables. The results suggested a spatial variation in transparency and total suspended solids. In areas heavily impacted by illegal gold mining, in downstream, water is less oxygenated (3.86±0.42 mg/L), less transparent (25.25±4.24 cm) with heavy loads of suspended solids (92.62±26.81 mg/L). The average level of mercury was estimated at 0.68±0.03 µg/L for this study. Ultimately, strong correlations have been observed between dissolved substances and transparency (r = +0.84), between total phosphorus and resistivity (r = -1.00) among other things. In the overall, the results showed that Bagoue watershed has not yet reached the critical threshold of physicochemical pollution. Nevertheless, a greater pollution gradient downstream than upstream has been observed. In addition, waters of the basin are gradually enriching in mercury.

water quality, mercury, artisanal gold mining, Bagoue River, Côte d’Ivoire