SEDIMENT CHARACTERISTICS AND STATUS OF WATER QUALITY IN NORTH REGION OF NEGOMBO ESTUARY, SRI LANKA

Abstract

Input of land based pollutants such as domestic and industrial sewage can have adverse impacts to the estuarine environment and detrimental impacts to species living in estuaries. The objectives of this research were to evaluate physico-chemical parameters and heavy metal contents of overlying water and sediments to identify the sediment characteristics, status of the water quality and to identifying its suitability for aquatic organisms in the north region of Negombo estuary during January to March 2019. Physico-chemical parameters and heavy metals in overlying water as well as sedimentary composition and four (4) heavy metal concentrations in six locations in the north region of Negombo estuary were investigated using appropriate standard techniques. The underlying patterns of physico-chemical parameters in both overlying water and sediment was examined using univariate and multivariate approaches. Results indicated that, mean temperature, salinity, electrical conductivity, turbidity, Total Suspended Solids, pH, Dissolved Oxygen, BOD5, ammonical-N, nitrate-N, nitrite-N and orthophosphate in overlying water within the permissible levels of CEA Ambient Water Quality Standards for Inland Waters in Sri Lanka (2017). Also, the concentrations of Chemical Oxygen Demand and Oil and Grease are slightly higher than the desirable levels. Further, the concentrations of Cd, Pb and Cu in overlying water and sedimentary Cd and Pb found to be exceeded of their acceptable levels. The average percentage of sand, silt and clay in the estuary sediment was 84.4 ± 2.7%, 1.15 ± 0.90% and 14.50 ± 2.33% in respectively. Average amount of Total Organic Carbon (TOC %) in the sediment was found as 2.05 ± 1.24%. However, TOC % showed significant positive correlation with clay (r = 0.928) but significant negative correlation with sand (r = –0.974). Further, sedimentary Pb showed significant positive correlation with TOC % (r = 835) while significant negative correlation with sand (r = –893). In conclusion, both overlying water and sediment of the north region of the Negombo estuary are contaminated in terms of heavy metals most probably due to anthropogenic activities and not suitable for the survival of aquatic organisms