Assessment of biannual seasonal variations in hydrochemistry of Kerwa reservoir located in hard rock formations of Central India

Abstract

An investigation on the Kerwa reservoir water located in central parts of India (Bhopal, Madhya Pradesh) has been carried out to assess the hydrochemical variations in different seasons and possible influencing factors. Temporal chemical variations in reservoir water were evaluated for all the three seasons by analyzing two hundred forty surface water samples from ten different sites along the reservoir periphery covering inlet and outlet points. The analytical results indicate that Kerwa reservoir water is mildly alkaline, and the order of dominance for ions was found to be Ca2+ > Mg2+ > Na+ > K+ and HCO3− > Cl− > SO42−. The major chemical facies present are Ca-Mg-HCO3, Ca-Mg-Na-HCO3-Cl, Ca-Mg-HCO3-Cl, and Ca-Mg-Cl-HCO3. Piper and Chadha plots infer that seasonality exert a strong control on the water chemistry. Rainwater dominate the reservoir water chemistry during monsoon, evaporation dominates during summer, while multiple geochemical reactions control the reservoir water chemistry during winter. The extent of ion exchange was evaluated by chloro-alkaline indices as well as (Ca2+ + Mg2+)/(Na+ + K+) versus Na+-Cl− plot. Contribution of carbonate and silicate minerals was evaluated using characteristic ionic ratios and scatter plots. It is found that weathering of silicate rocks lead to higher Ca2+ and Mg2+ in the reservoir water, while evaporite dissolution and to a some extent ion exchange and base flows are found to control the Na+ and K+ concentrations. With the growing scenario of contamination in adjoining water bodies, the study on water quality and associated geochemical processes becomes necessary for Kerwa reservoir, which can form a potential freshwater reserve in this region for future generations.