A study of water quality of Bolgoda North Lake

W.M.P. Gunatilaka, S. Chandrani Wijeyaratne


Bacterial populations were investigated in relation to the environmental parameters in BolgodaLake for a period of six months from January 2000 to June 2000. Surface water samples werecollected from six sampling stations in the Bolgoda Lake at monthly intervals. Total viablebacterial colony forming units (assumed to be equal to the density of bacterial population),total coliforms and faecal coliforms were studied as biological indicators. Physico-chemicalenvironment parameters included, temperature, pH, electrical conductivity, salinity, Secchidisk depth, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygendemand (COD), orthophosphate and nitrate contents. These were measured using standardmethods. Correlations among bacterial densities and selected water quality parameters wereinvestigated. High densities of bacterial populations were recorded at several sampling pointsin the vicinity of outlet drains which bring domestic and industrial effluents. Low densities ofbacterial populations were recorded in samples taken at upstream and downstream of the NorthLake. Results also revealed that some chemical parameters may have an effect in the density ofbacterial populations. Density of bacterial populations showed a significant negative correlationwith Biochemical oxygen demand (BOD) and with phosphate concentration. However, thedensity of bacterial population did not show a significant correlation with the nitrate content ofthe surface waters of the Lake. Further the DO, BOD values and PO4-3 content indicated organicand inorganic nutrient pollution of surface waters of Bolgoda Lake. However, samples collectedfrom downstream had lower values for above parameters indicating that self- purification istaking place to a certain extent in the Lake. However, results revealed that at present BolgodaLake is heavily exposed to pollution from industrial and residential effluents. To avoidcatastrophe, measures should be taken to reduce pollution by curtailing sewage disposal andtreatment of effluents of nearby factories before being discharged into this Lake.
Key words: water quality, Bolgoda Lake, evaluation of water quality


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