Ecological Risk Assessment of Heavy Metals in Sediments from the Soubeira Reservoir, a Small-Scale Reservoir in North Central Burkina Faso, West Africa

Small-scale reservoirs play a central role in socio-economic development of Burkina Faso. In the absence of a best environmental management plan, these reservoirs can be potential factors of water pollution and ecological deterioration. In the present study, we investigated ecological status of sediments from the Soubeira reservoir, using concentrations of a series of heavy metals. Concentrations of the metals ranked as follows: Fe> Mn> Cr> Zn> Cu> Pb> As ~ Co> Hg ~Mo> Cd. Based on the correlation analysis, Fe, with weaker relationships with other metals, may be derived from the local ferruginous soil, whereas Cd, Cu and Cr could be mainly originated from anthropogenic sources and carried by clay minerals into the reservoir. In contrast, Hg and As abundance could be related to artisanal gold mining in the surrounding environment. Negative correlations between heavy metals (except As) with pH were consistent with desorption and mobility of the majority of heavy metals under low pH values. The significant negative correlations were also observed between CEC and As (r = - 0.75) and between clay and As (r = -0.64). This could be an indication of As mobility under the physico-chemical conditions of the reservoir. Both potential ecological risk and adverse effect indices suggested that the reservoir sediments were highly polluted. Five heavy metals (As, Cd, Cu, Cr and Hg) could cause adverse effect to biota, whilst only Hg and Cd appeared to show high and moderate potential ecological risk indices, respectively. The study demonstrated that the Soubeira reservoir requires a heavy metal pollution control program.