Ca Budget, Factors of Calcite Precipitation in a High Altitude Himalayan Lake

Hard water lakes are known to precipitate Ca through a complex number of factors. Dal, a shallow Himalayan hard water lake was observed to remain saturated with respect to calcium carbonate CaCO3 [(S.I.) range: 0.1 – 0.7, avg. 0.3] throughout the study period of Sept. 1999 to Aug. 2000. CaCO3 precipitating tendency of lake waters primarily results from high surface loading of 422.7g Ca m yr, which was mainly accounted by colossal export of 25.3 g Ca m yr from its Telbal-Dachigham sub-catchment. Maximum saturation levels of lake waters were observed from mid spring through summer, and were concomitantly brought about by Ca loading of 4169 tonnes (59.4% of total loading yr), high temperatures and photosynthetic activity of dense macrophyte biomass (3.2 kg m). Increase in the saturation level of lake waters during spring-summer period was observed to be a linear function of water temperature (r = 0.85, p <0.05) and hydraulic residence time (r = 0.93, p<0.05). Increase in the saturation levels of lake waters were observed to bring significant reductions in Ca (r = -0.88, p<0.05) and PO4-P (r = -0.93, p<0.05) through Ca-P precipitation. This loss of Caand PO4-P was also confirmed by observing high retention of 2021.5 tonnes of Ca yr, out of which about 1450 tonnes i.e. 72% flux was estimated during peak saturation levels. Keeping in view, the role of Ca in lake management, this paper therefore, describes Ca transport from various sub-catchment and inter alia interactions of Ca, macrophytes, PO4-P, temperature, and hydraulic residence within the lake system. The sequence of these interactions is used for suggesting management options for the lake.