Assessment of Surface Water Quality by Evaluating the Physico-Chemical Parameters and Identify the Impacts of Water Pollution

Abstract

Lunawa lagoon is situated about 19Km from Colombo city. It is about 2500m in length and about 100-250m in width. The lagoon is one of small wetlands site in Sri Lanka. In present the lagoon environment has become deteriorated by human and natural phenomena. The Lunawa lagoon and its catchment area in Rathmalana are compacted with various industrial zones and homestead.  It has therefore become necessary to assess the quality of water in the lagoon and the surrounding fresh water aquifer.  This lagoon was a main source of fishery before 1980's. There are three main cannels directly connected to the lagoon, Elu Ela, Lunawa Ela, Hemin galena Ela. Surface water quality in this region is largely determined both by natural processes (weathering and soil erosion) and by anthropogenic inputs (municipal and industrial waste water discharge). The objectives of this study have been evaluated the surface water quality in terms of physiochemical parameters of the Lunawa lagoon.  Beside this, the work also highlights and draws attention towards the correlation with rainfall and the water quality index. Some physical parameters measured in situ and some selected chemical parameters were done in laboratories. Water quality was surveyed from October 2015 to March 2016 by using at eight different sample points. A total of six water quality parameters namely, water temperature, pH, Electrical Conductivity (EC), Dissolve Oxygen (DO), Salinity, Turbidity were measured in-situ. While for laboratory analysis there were five chemical parameters namely, nitrate, phosphate, Total Dissolve Solids (TDS), Biological chemical oxygen demand (BOD), and Chemical oxygen demand (COD). Along with this work identified the major impacts of water pollution in the lagoon. According to the results, the results of various water quality parameters of the Lunawa lagoon considerably fluctuation in pH among 8 sample points. The pH level range falls into 7.1-7.7. The average range of EC was 3µs/cm-32µs/cm. TDS were recoded high values in stagnant water locations. Water Temperature was having an average 29.4°c – 29.6°c respectively. DO average level was 1.4mg/l – 3.2mg/l across the sites. Turbidity range was 27.4NTU-7.3ntu respectively. The salinity average range was 10.4ppm-28.4ppm. The nitrate concentration was high in the southern part and the phosphate concentration was high in the northern part of lagoon. The BOD and COD in pure water should be within 15mg/l-30mg/l and 3mg/l-5mg/l, but average in the lagoon was 281.81mg/l and 44.81mg/l respectively. There were high negative correlations between   pH and rainfall (r = -0.81), EC / rainfall (r = -0.83) and high positive correlation between turbidity / rainfall (r = 0.99), dissolve oxygen / rainfall (r = 0.92). According to the Water Quality Index in the lagoon, water is not suitable for drinking, bathing, aquatic and agricultural purposes.