Physicochemistry and water quality of Loktak Lake water, Manipur, India
Bhagita Mayanglambam, Siva Siddaiah Neelam
Abstract
A total of 32 surface water samples (pre – and post-monsoon) from different locations of Loktak Lake, Manipur, were studied for physicochemistry and water quality to assess its potability. Parameters, namely, water temperature, pH, electrical conductivity (EC), major ions (Ca2+, Mg2+, Na+, K+, HCO3ˉ, Clˉ, NO3ˉ, PO43ˉ and SO42ˉ), dissolved silica (H4SiO4) and potentially toxic elements (Fe, Mn, Cu, Zn, Ni, Cr, Co, Cd and Pb) were analysed. The water is neutral to alkaline in pre-monsoon and slightly acidic to alkaline in post-monsoon. Twenty-five percent of the post-monsoon samples have a higher pH than the WHO acceptable limit. The water is soft with low EC and total dissolved solids (TDS). The pre-monsoon samples have a relatively higher concentration in the majority of parameters studied except HCO3ˉ, SO42ˉ, NO3ˉ, PO43ˉ, dissolved organic carbon and dissolved inorganic carbon. The concentration of cations (mg/L) follows an order of Ca2+> Mg2+> Na+ > K+ and that of anions HCO3ˉ > Clˉ > NO3ˉ > PO43ˉ > SO42ˉ. The concentration of Pb in the majority of samples was above the acceptable limit for drinking. The lake water chemistry is mainly derived from rock-forming minerals besides anthropogenic sources. Carbonate weathering dominantly influences the water chemistry along with a minor contribution from silicate weathering. The main hydro-geochemical facies is Ca-Mg-HCO3. The sodium adsorption ratio, Na%, residual sodium carbonate and the Wilcox diagram indicate the suitability of Loktak water for irrigation. Based on the water quality index, the majority of pre-monsoon samples are of poor category contrary to the post-monsoon samples which are of good category. Therefore, for its potability, pre-monsoon waters from the river inlets, the national park region and the lake’s northeastern portion and post-monsoon waters from the Phubala River inlet and near the Thanga Island require pre-treatment.