Limnology of Kandy Lake before the outbreak of cyanaobacteria bloom in May 1999. II Photosynthetic primary production

In situ photosynthetic rates and chlorophyll-a contents of planktonic algae were determined monthly for two consecutive years (September 1996 — August 1998) employing light-dark bottle technique in Kandy Lake. The objective of the study was to determine the photosynthetic characteristics and subsequent primary production under prevailing climatic and hydro-ecological regime of this urban man-made eutrophic water body.

Photosynthesis occurred mainly to a 4 m depth with light saturated maximum rate at subsurface water under clear sky indicating surface inhibition. Chlorophyll-a (chl-a) content, and photosynthetic rates were relatively low during the rainy 'seasons compared to dry weather conditions. However, both parameters showed a progressive increase towards the end of the study period. With respect to chl-a content (16-45 µg l-1) and specific photosynthetic rates (4-42 mg mg-1 chl-a hr-1), Kandy lake was eutrophic during the study period. However, area based net primary production was always positive (0.073-1.775 g 02 m-2 hr- 1) with a daily mean gross value of 9.80 g 02m-2 d-1 (± 6.20).