Surface water quality analysis of an urban lake; East Beira, Colombo, Sri Lanka
2019
Weerasinghe, V.P.A. | Handapangoda, Kosala
The Beira lake is an urban lake as a sponge to control flooding in the area as well as one of the wastewater receiving water bodies in Colombo, Sri Lanka. Present study, aims to assess the spatial and temporal variability of water quality parameters of East Beira lake. Selected surface water quality parameters of the East Beira lake namely, temperature, pH, total dissolved solid, conductivity, salinity, Secchi disc visibility, biochemical oxygen demand, chemical oxygen demand, dissolved oxygen, nitrate-Nitrogen, and total phosphorous were measured at 08 judgmental sampling sites for a period of 06 months from May to October 2017. Sampling frequency was 06 weeks. Spatial and temporal variability was assessed using two-way ANOVA followed by Tukey’s pairwise comparison. To derive continuous surfaces for water quality parameters, Kriging interpolation technique was applied using GIS software. Moran’s index was used to observe the spatial autocorrelation and revealed that surface temperature, salinity, conductivity and total dissolved solids show clustered spatial pattern and total phosphate and COD show slightly clustered spatial pattern of the lake. Kriging interpolated maps show similar pattern of distribution as shown by Moran’s index since both geostatistical methods use autocorrelation statistics. Cumulative effect of anthropogenic activities, lake morphology and catchment characteristics, might be resulted in the spatial variability in lake surface water TDS, conductivity, salinity, COD, and total Phosphate mean values. Rainfall pattern affected for the temporal variation of the surface water temperature, pH, total dissolved solids, conductivity, salinity, visibility, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand and total phosphate. Management strategies of pollution reduction are proposed for the point sources which create clustering pattern of pollution, in combination with systematic real time monitoring, in order to upgrade the eco system of the East Beira Lake.
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