The Chlorophyll-a Content, Species Composition and Population Structure of Phytoplankton in Randenigala Reservoir in Sri Lanka

Abstract

Preliminary investigations of phytoplankton composition their population densities, chlorophyll - a, content and seasonal fluctuation of the phytoplakton were carried out in Randenigala reservoir. Vertical and horizontal sampling was performed at different locations,in three major stations and in eight sub stations at monthly intervals from May to December 1992. The phytoplankton groups in the reservoir belong to Chlorophyceae, Cyanophyceae and Bacillariophyceae. The most abundant taxonamic group in the reservoir was Chlorophyceae and the Straurastrum limneticum was the most prominent species. When the vertical distribution was concerned, the highest phytoplankton density was observed in the surface epilimnetic waters upto about 10m depth and it declined with increasing depth.Fluctuation of seasonal phytoplankton densities and production of phytoplankton pulses ofCosmarium species andstraurastrum species were observed during May to June and September to October 1992.The highest chlorophyll - a content was recorded in May and it remained at a low level bellow 0.1 ug/l through out the investiga tion period. During _some occasions there was no clear-cut inverse relationship between chlorophyll a content and transparancy values of the reservoir. The species diversity, high transparancy values and low nutrient conditions of Randenigala reservoir indicates that its trophic nature is perhaps far from eutrophic status.