Abstract:
Lake Nainital is one among a group of lakes occurring in the southern fringe of the Kumaun Lesser Himalaya. The maximum length of the lake is 1.4 km, maximum width 0.45 km, maximum depth 27.3 m and mean depth 18.52 m. The lake surface area is 0.46 km2 and total catchment area is 4.7 km2. Lake Nainital is the only source of drinking water for the city. In the past few decades, unplanned developments and urbanisation in the lake catchment have caused serious problem related to pollution, eutrophication and accelerated sedimentation etc. The temperature data revealed that Nainital lake undergoes two distinct stages, viz., complete mixing stage during December to February and stratified stage in other months during a year. pH indicates alkaline nature of lake water. Among the major cations, Ca++ and Mg++ dominate over Na+ and K+, and among the major anions HCO3" dominates followed by SO4, CI- and NO3". The seasonal variation in HCO3" is mainly due to the phytoplankton activity in the lake. The chemical data of the lake water since 1950 revealed that there is continuous increase of nutrients (nitrogen and phosphorus), due to domestic and other effluents discharged in to the lake through various drains. Higher concentration of K+ observed in monsoon as compared to other seasons is also due to increased transport of refuse by the storm runoff into the lake. The total phosphorus recorded, more than 127 14/1, indiCates that the lake has entered in the hypereutrophic condition. The Carlson TPTSI used for determining trophic state index of the four lakes revealed that lake Nainital is the most eutrophic lake in the Kumaun region (74) followed by Bhimtal lake (51), Khurpatal (44), Sattal (32) and Naukchiatal (20). Thus the hypereutrophic stage of lake, continuous increase in nutrients, decrease in secchi depth clearly indicates that the anthropogenic activities have greatly affected the lake physico-chemical characteristics.
