Nuisance algae in water supply projects in Sri Lanka

Abstract

Sri Lanka is a tropical continental island which consists of 103 rivers and about ten thousand man made tanks. There are over 250 water supply systems constructed using these water bodies since later part of the nineteenth century, reservoirs which are used extensively for domestic and agricultural practices. It is reported that most of these water sources are constantly becoming contaminated with different types of algae making the water unsuitable for human consumption. The present study was carried out to identify toxin producing, filter clogging, taste and odor forming nuisance algae and some physico-chemical parameters in some selected water bodies namely Labugama, Kalatuwawa, Parakramasamudra, Kondawatuwana, Mahaweli intake at Neelapola and Kantale. Sampling for algae and physico cemical parameters were carried out for a period of one year from April 2009 to April 2010. The results of the present study showed that all physico-chemical parameters in the water bodies were within the drinking water quality standards recommended for Sri Lanka. However Species diversity and density of phytoplankton was different in the water bodies. In Labugama and Kalatuwawa, total algae population consisted 10% of cyanotoxin producing Microcystis aeruginosa, 10%, 20% and 60% of taste and odor forming Peridinium sp., Microcystis sp. and Staurastrum species respectively. In contrast, 89% of cyanotoxin producing cyanobacteria in Kondawatuwana tank, 50% in Parakramasamudra, 40% in Neelapola and 95% in Kantale were detected. Total filter clogging algae in Parakramasamudra, Neelapola, Kondawatuwana and Kantale were 29%, 69%, 72% and 15% respectively while taste and odor forming algae were 22%, 36%, 72% and 11% respectively. Among the water bodies under study Neelapola recorded the highest occurrence (34%) of filter clogging diatom while the highest percentage of cyanotoxin producing M. aeruginosa (62%) and Cylindrospermpsis sp. (85%) were recorded from Kondawatuwana and Kantale tanks respectively. During the study period, the lowest percentages of toxic producing algae were recorded from Labugama and Kalatuwawa reservoirs which are exclusively used for drinking purposes indicating their suitability as drinking water sources. In contrast, the highest percentages of toxin producing, filter clogging and taste and odor forming algae were recorded in Kondawatuwana drinking water tank. As for the other water bodies studies showed that there is no immediate threat due to algae.