K. D. N. Weerasinghe

Stresses over surface water sources in a human dominated environment: A case study in Hamilton canal, Sri Lanka

Purpose The Hamilton canal in the western province of Sri Lanka is a man-made canal situated in an area with immense anthropogenic pressures. The purpose of this study is to identify the quality variations of the water in Hamilton canal and human perception about the present status of the water of the canal. Design/methodology/approach Sampling has been carried out in seven locations in the canal during dry and wet periods for water quality analysis. In situ field-testing and laboratory analysis have been conducted for physicochemical, heavy metal, oil and grease analysis of water. Only Pb, Cd, oil and grease were tested in the canal sediments. The samples were analyzed as per the standard methods of the American Public Health Association (APHA) Manual: 20th edition. A semi-structured questionnaire survey has been carried out to assess the human perception on the water of the canal. Findings The results revealed that average EC, Turbidity, Total Hardness, TDS, F−, Fe2+, Cl−, SO42− and PO43− of the canal water remained above the threshold limits of inland water standards. Concentrations of Pb and Cd were also above the standards in some locations. Oil and grease were in a very high level in water and sediments. Originality/value The water of the canal has been affected by nutrient, heavy metal and oil and grease pollution at present. Discharge of domestic, industrial, municipal wastes and sewage are the prominent reasons which have encouraged the deterioration of the quality of water in the canal.

Mangrove Diversity Across Salinity Gradient in Negombo Estuary-Sri Lanka

The study was conducted in the Negombo estuarine lagoon locates in the Gampaha District of Sri Lanka. In this research, an investigation was carried out to identify and assess the distribution pattern of mangrove diversity across salinity gradient in the lagoon. A field survey was performed to collect primary data and vegetation sampling was carried out in two transects along the periphery of the lagoon. Located sample size is 5 m × 10 m. Fifteen samples were selected maintaining distribution of species heterogeneity. Only mangrove species were enumerated. In situ field-testing of salinity was carried out at monthly intervals during October 2012 to September 2013 for 15 samples. Shannon-Wiener diversity index was calculated to compare about the diversity of mangrove species. The Inverse Distance Weighted (IDW) interpolation technique in ArcGIS was performed to prepare spatial distribution maps. There are 18 mangrove species identified belonging to 14 genera and 12 families. Among them 14 species are “True” and 4 species are “Mangrove Associates”. Rhizophora mucronata, Rhizophora apiculata, Avicennia officinalis, Excoecaria agallocha and Acrostichum aureum are the most common species and Aegiceras corniculata, Aegiceras corniculata, Bruguiera sexangula and Xylocarpus granatom are the least common true mangrove species types found in the Negombo lagoon. Spatially the highest mangrove species diversity could be identified in the southern quarter and a small patch around the outlet of the lagoon. Relatively low species diversity is identified at the middle periphery of the lagoon. Spatial differences of the floristic composition and the diversity reflect the salinity tolerance ability of the different mangrove species.

Impact of Natural Processes and Human Activities on Groundwater Quality in the Negombo-Muthurajawela Region in Sri Lanka

Groundwater is an essential and finite resource in the world. Numerous knowledge gaps remain in the understanding of groundwater resources in Sri Lanka, mainly due to the lack of accurate data. The purpose of this study is to assess the water quality in groundwater and its spatial distribution in Negombo-Muthurajawela area in Sri Lanka. The data collection was conducted at the beginning and at the end of south west monsoon (May and September, respectively) in 2013. A pilot survey was carried out using 116 dug wells. A total of thirty-one dug wells were selected for physiochemical analysis. In situ field testing of electrical conductivity (EC), salinity, and pH were carried out and laboratory tests were performed for HCO3−, Na+, K+, Ca2+, Cl−, SO42−, Mg2−, PO43−, NO3−, and total hardness (TH). Principal component analysis (PCA) was performed to assess water quality and interpolation technique in ArcGIS was performed to analyze and prepare spatial distribution maps of water. Sri Lankan standards for drinking water were used to determine the threshold levels of physiochemical parameters. The results of the PCA reveal that thirty-one observation wells can be classified under three main components: the first based on the impact on EC, HCO3−, Na−, K+, Cl−, Mg2−, and TH; the second component considering the pH, HCO3, Ca2+, SO42−, PO43−, and TH; and the third component based on NO3−. These three components evidence the role of salt water intrusion, the influence of Muthurajawela wetlands, and the anthropogenic discharges on groundwater quality in the Negombo-Muthurajawela area.

Role of Sea Level Rise on the Groundwater Quality in Coastal Areas of Sri Lanka

Coastal areas are among the world’s most productive but ecologically fragile regions. Coastal groundwater is a dynamic and replaceable resource. Ground water is the largest source of fresh water available on earth, which is exploited to satisfy domestic, agriculture and industrial purposes. Ground water plays a significant role in the overall circulation of water through the hydrologic cycle. It is always considered as a readily available and safe source of water for domestic, agricultural and industrial use (Bear, 1979; Gavich et al., 1980). Groundwater will be less directly and more slowly impacted by climate change as compared to surface water, but in coastal areas ground water will be directly affected by sea level rise. Sea level rise would directly affect the coastal river basin areas and increase saline water intrusion to the coastal areas of Sri Lanka. Sea water intrusion in coastal areas of Sri Lanka cause serious problems to various sectors of natural and anthropogenic environments.