Monitoring of The Safety and Quality of Water of La Ferme Impounding Reservoir of Mauritius

Water supply from La Ferme impounding reservoir is primarily intended for agricultural use. Unfortunately, there is a concern that the reservoir water is potentially befouled by agrochemicals and pollutants from nearby farms, feeder canals and a solid waste transfer station. The nutrient influx into La Ferme could favour the growth of toxin-producing cyanobacteria which could eventually jeopardize human and animal health. This research is aimed at assessing the water quality of La Ferme reservoir. Water was sampled at the intake tower and two rivers that discharge into La Ferme during summer/rainy (November–April) and winter/dry (June–September) seasons. The mean cyanobacterial count and level of orthophosphate, nitrate and total organic carbon in the reservoir were 63,738 cells/mL, 0.065 mg/L, 0.125 mg/L and 4.8 ppm, respectively. Orthophosphate and total organic carbon levels were significantly positively correlated with cyanobacterial cell counts. The mean orthophosphate level in reservoir water was found to be significantly higher (p ≤ 0.05) during rainy seasons (0.08 mg/L) compared to dry seasons (0.04 mg/L). Residues of herbicide tebuthiuron and cyanotoxin microcystin-LR were also detected with a mean concentration of 0.15 and 0.3 mg/L, respectively. This study highlights the potential eutrophic status of La Ferme reservoir and contamination of its watersheds by microalgal toxin and herbicide that could compromise the ecological integrity of the reservoir and negatively impact the sustainable use of this natural resource.