Analysis of physicochemical parameters and selected potentially toxic elements to assess the water quality of Kattakaduwa reservoir in Hambanthota district, Sri Lanka

The study was aimed to assess the water quality of Kattakaduwa reservoir in Hambantota district, Sri Lanka. Reservoir water is not directly used for drinking purposes until purification, but people use it for different purposes such as bathing and irrigation. A comprehensive study on the water quality of this reservoir water was timely needed due to the scarcity of such information. Monthly variation in seven physicochemical parameters and five potentially toxic elements (Mn, Fe, Cu, Cd and Pb) of water at five different sites compared to treated reference water samples were studied for 2017. Sediment analysis of the five elements at four different sites was also carried out. At the site closer to the inlet of the pump house before purification (site 3S), the mean values (± SD) of water temperature, pH, dissolved oxygen, sulphate concentration, turbidity, conductivity, and alkalinity were 33 ± 1°C, 7.5 ± 0.1, 7.19 ± 1.80 mg/L, 57.40 ± 23.60 mmol/L, 36.74 ± 18.87 NTU, 605.3 ± 119.8 µS, and 176.0 ± 32.0 mg/L, respectively. The maximum Fe concentration was observed in March (1.73 mg/L) while the minimum was in January (0.70 mg/L) exceeding the United States federal limits (USFL) and Sri Lankan Standard level (SLSL) of Fe (0.3 mg/L) throughout the year. However, Mn concentration in the same site exceeded the USFL and SLSL (0.05 mg/L) slightly in May, July, and October. The concentrations of the rest of the elements were below the minimum detection limit (MDL) of 1 mg/L. All elements in the treated reference water sample (TR) were below MDL. The concentrations of Fe (15291 ± 10486 mg/kg) in sediments were greater than Mn (1178 ± 1007 mg/kg). These values reflect the higher Fe concentration in the reservoir water compared to Mn concentration that may be due to the leaching of Fe from the sediments to the water.