Effect of Urbanization on Water Quality of Selected Canals in Colombo and its Suburbs; with Special Reference to Diatoms

Abstract

Diatoms are widely used in monitoring environmental contamination and serve as bio-indicator for water quality and pollution status and they are more sensitive to the small variations in the environment as compared to other macrophytes and benthic algae. Objectives of this study were (a) to identify diatom species found in canals of Colombo with varying water quality and (b) to identify the species variations within rural, suburban and urban canals. Variations in water quality parameters, nutrient content and organic matter content were expected between canals due to different degrees of urbanization. Three canals were selected in Colombo area according to the varying degree of urbanization and four sites in each canal were selected. Diatom, water and sediment samples were collected, whereas, diatoms were analysed and abundance values were taken. Dissolved oxygen (DO %), DO (mg/L), pH, conductivity and salinity values were determined as the water quality parameters. Weight ignition method was used to measure organic carbon content of canal bottom sediment. There was no significant difference observed in mean values of the trophic diatom index (TDI) between the three canals. Furthermore, water quality parameters between canals except for salinity and conductivity were observed with no significant difference between the canals. A significant difference in nutrient content and the organic matter content was identified between canals. Furthermore, nine diatoms were identified up to genus level according to their morphology. Even though it was expected to have species distribution differences between three canals credited to varying water quality parameters, there was no significant difference in species distribution was observed between the canals. Identification of diatom species up to their species level might help to have more accurate diatom diversity and environmental evaluation within and between canals. Furthermore, it is recommended to continue this study in both monsoon and inter-monsoon with more environmental parameters to have a better understanding about the variation on environmental parameters with species diversity and to determine more parameter changes according to the degree of urbanization.