Assessment of ecohydrogeochemical status of freshwater Loktak Lake of Manipur, India.

Abstract

The present study has been carried out to assess the ecohydrogeochemical status of Loktak Lake, the largest freshwater lake in the Northeastern region of India, based on the water quality parameters, hydrogeochemistry, water quality indices (WQI) and trophic state index (TSI). The spatio-temporal variations of physicochemical parameters have been assessed, and it was found that parameters such as pH, turbidity, dissolved oxygen, biological oxygen demand, iron, fluoride and coliform concentrations in the water exceeded the permissible limits prescribed by the World Health Organization (WHO) and Bureau of Indian Standards (BIS) during both pre-monsoon (PM) and post-monsoon (PoM) seasons. The water hardness lies within the soft category, except for a few samples found to be moderately hard. WQI values of lake water ranged between 38.19 and 155.47 during PM and 39.48 and 432.26 during PoM. Based on the WQI classification during PM, 8.6% of the samples were in the unsuitable category, 14.3% very poor, 45.7% poor and 31.4% in the good category. During PoM, 22.9% of thesamples were in the unsuitable category, 25.7% very poor, 31.4% poor and 20% in the good category. The irrigation water quality was evaluated using indices such as sodium percentage, sodium adsorption ratio, residual sodium carbonate, permeability index and Kelly's ratio, and the results indicated that the lake water could be used safely for agricultural purposes. The trophic state evaluation revealed an oligotrophic condition of the lake waters during PM (TSI 37.9) and a mesotrophic condition during PoM (TSI 46.9).