Assessment of water quality and trophic state in Sooriyawewa reservoir in the Southern province of Sri Lanka

Trophic state of a reservoir is one of the important factors in limnological perspective in order to understand its healthiness. This study was focused to understand the dynamics of trophic state and water quality in Sooriyawewa reservoir in the Southern province of Sri Lanka. Water quality was evaluated in six sampling sites from August 2014 to March 2015 using standard methods. Significant temporal variation (p -1 ), NO 3 - (2.77±1.4 mg L -1 ), PO 4 3- (0.21±0.1 mg L -1 ), total suspended solids (15.24±10 mgL -1 ), conductivity (253.75±86.2 µScm -1 ) and temperature (29.90±0.5°C). PO 4 3- , NO 3 - and chlorophyll-a concentrations showed their highest levels in September, October and November respectively. Water Quality Index (WQI) values ranged from 11.62 (December) to 22.78 (November, January, February, March) indicating very poor water quality. The Trophic State Index (TSI) changed from slightly eutrophic to hyper-eutrophic status in October and November respectively coinciding higher chlorophyll-a concentration. Results showed that Sooriyawewa reservoir is not suitable to be used as a drinking water source under conventional treatment and continuous monitoring of water quality parameters should be carried out.