Limnology of Kandy Lake before the outbreak of cyanobacteria bloom in May 1999. I. Physicochemical characteristics

The Kandy Lake, a man-made water body, located in the heart of the second largest city of the island adjoining the world-renowned Buddhist temple, was examined for its physicochemical characteristics. Monthly sampling was carried out at four sites for a period of two years (September 1996-August 1998) and physicochemical characteristics and nutrient concentrations were analyzed to determine the spatial and temporal patterns of the basic limnological features. Physicochemical characteristics of surface water in the Kandy lake did not show significant spatial variability depicting a homogeneous nature but, marked vertical gradients of some parameters were noted in the deeper basin. Although, annual range of surface temperature varied within the tropical range, a temperature/ density micro-stratification was prominent under calm conditions.
Bicarbonate and calcium dominant alkaline lake water was about three fold conductive than the inland surface waters found at similar elevations. Alkaline water becomes acidic in the deeper layers and the water column of the deep basin was characterised with a clinograde oxygen profile with the incidents of anoxia. The ratio of total inorganic-N to total-P indicated phosphorous limiting conditions but concentrations of reactive phosphorous were available for 'rapid uptake by phytoplankton. The dynamic fluctuations of NO2-N and NO3-N and the upper limit of NH4-N, the most dominant nitrogen species indicate extremely high heterotrophic potential in the bottom water under less oxygen conditions.