Trophic Status of Beira Lake

Abstract

Beira Lake is located in the heart of the city of Colombo.and in an highly urbanized catchment of 432 ha. Beira Lake covers 65.4 ha and comprises four main basins the East Lake, the Galle Face Lake, the West Lake and the South West Lake. The objective of the study was to determine the trophic status of the lake using the, physical, chemical and biological properties of the water. The mean water transparency depth of the lake was 15.2±9.2 ern. The euphotic zone was approximately 41.8 cm. Water temperature ranged from 26°C to 32°C. Conductivity ranged from 212 to 500 IlS. pH value ranged from 7.2 to 9.8 Dissolved Oxygen, BOD and Orthophosphate values of the lake ranged from 7.82 to 14.41 mg/I, 33.45 to 68.35 mg/1 andO.014 to 0.08 mg/l respectively. The highest and lowest Sulphate values recorded were 4.04 ppm and 2.33 ppm. The Chloride content ranged from 29.02 to 53.09 mg!. The phytoplankton community of the Biera Lake composed of the dominant blue green algae and the green algae. Blue green algae represented 99 percent ofthe total phytoplankon population. The major zooplankton groups observed werecladocerans, Copepods and Rofiters. Copepods were the most dominant zooplankton group. According to the physical chemical and biological properties obtained for Beira Lake, it is at the advanced stage of eutrophication process.