Spatial and temporal variation of physicochemical parameters of coastal waters in the southwestern region of Sri Lanka

Abstract

Physicochemical parameters of coastal water in the southwestern area of Sri Lanka were studied from January to November 2016. Surface water samples from 15 selected locations were analysed according to standard methods. The ranges of the values recorded were; water temperature (WT) 26.5-33.9 ºC, pH 7.1-8.4, dissolved oxygen (DO) 4.4-7.4 mg L-1, salinity 14-38 ppt, electrical conductivity (EC) 27.1-53.8 mS cm-1, total suspended solids (TSS) 50.2-403.4 mg L-1, turbidity 1.2-64.9 NTU, nitrate nitrogen (NO3--N) 0.00-0.57mg L-1, nitrite nitrogen (NO2--N) 0.00-0.035mg L-1, ammoniacal nitrogen (NH4+-N) 0.00-1.72mg L-1, dissolved inorganic phosphorous (DIP) 0.00-0.65 mg L-1, biochemical oxygen demand (BOD) 0.1-11.6 mg L-1 and chemical oxygen demand (COD) 40-768 mg L-1. Results of Two-way ANOVA showed that there was a seasonal variability in parameters such as water temperature (p<0.001), dissolved oxygen (p<0.001), BOD (p<0.001), COD (p<0.001), nitrite nitrogen (p<0.001), nitrate nitrogen (p<0.001), dissolved inorganic phosphorous (p<0.001), turbidity (p<0.001), TSS (p<0.001) and Chlorophyll a (p<0.001). Spatial variation was identified in parameters, pH (p<0.001), turbidity (p<0.001), dissolved oxygen (p=0.004) and nitrite nitrogen (p<0.001) whereas the interaction between time and location was significant in pH (p=0.005) and turbidity (p=0.007). However, EC, salinity and ammoniacal nitrogen were not significant by either of the factors of consideration. In conclusion, the physicochemical characteristics of water are highly variable over time and location due to both natural and human factors. Water quality near fish processing areas such as fishery harbours and fish markets relatively deteriorated in terms of pH, DO, turbidity and nitrite nitrogen compared to recreational beaches. It is recommended to regulate any discharges of sewage and industrial wastewater directly into the sea. A long-term coastal water quality monitoring programme is vitally important to comprehensively characterise the coastal segments for a long-term strategic plan for sustainable development.