Salinity, pH and Turbidity changes of water in the Negombo lagoon



The Negombo lagoon is a lagoonal estuary, situated in the Gampaha District. It receives surface water runoff mainly from the Dandugam Oya, Ja-ela, Hamilton Canal, and the Dutch Canal. The present study was carried out to identify salinity, pH and turbidity of water in the lagoon during October 2012 and March 2013. Sampling was carried out in 20 locations.The overall average salinity levels of water varied between 15.34ppt and 15.53ppt in the surface and middle layers of the lagoon and 17.23ppt in the bottom layer. pH of water of all three layers fluctuated between 7.68 and 7.75. The highest overall average turbidity of water was 24.99 NTU that was recorded in the bottom layers. Average turbidity levels fluctuated between 10.44 NTU and 12.89 NTU in the surface and middle layers.Spatially, water salinity decreased from the outlet towards the southern periphery of the lagoon due to dilution. However, it was comparatively high in the south west region possibly due to the influx of water from the Hamilton Canal. Water salinity increased from top to bottom of the lagoon due to the density of water. In the northern half of the lagoon, a relatively high pH was observed. However, a considerable relationship of pH could not be identified from surface to bottom layers during the considered period. The turbidity of lagoon water demonstrated an increasing trend from the northern outlet towards the southern fringe. The water in the lagoon appears to be directly influenced by the sediment discharged by Dandugam Oya, Ja-Ela Canal, and Hamilton Canal. Based on the salinity, pH and turbidity of the wate,r the Negombo lagoon can be differentiated into two regions. Overall, the spatial distributions of salinity and pH levels of lagoon water have a negative relationship with turbidity.