Mapping of Water and Soil Quality Parameters in the Gampaha-Ihalagama East and Eldeniya East Grama Niladhari Divisions, Sri Lanka

Water and soil are important natural resources, and the study of their distribution is of great interest. The Grama Niladhari Divisions, Ihalagama-East and Eldeniya-East, located in the Gampaha district, are selected as the study areas, and this is done as a pilot study. Different water and soil quality parameters are investigated followed by the construction of contour maps. As water quality parameters, pH, conductivity, phosphate content, nitrate content, and Ca2+ hardness were determined, and as soil quality parameters, pH, nitrate, organic matter, water-soluble Na+ and K+, extractable Na+ and K+, and water-soluble Ca2+ ion contents were determined. The pH of water samples lies within the range of 4.41 - 7.11 and 3.79 – 7.18 in the Ihalagama-East and Eldeniya East divisions, respectively. Almost all the samples have acidic pH values, with some falling below the lower limit of the WHO guidelines for safe drinking water (6.5 - 8.5). Conductivity values vary from 52.0 - 277.0 µS/cm and between 54.0 – 403.0 µS/cm, respectively, which is below the WHO permissible level of 1500 µS/cm. The phosphate content varies from 1.374 - 3.986 mg/L in Ihalagama-East and water-soluble phosphate was not detected in Eldeniya-East, indicating a very low range and suggesting that the water samples are less contaminated with phosphate-containing substances. Considerably high values in the range of 1.24 - 279.00 mg/L for Ihalagama-east and 59.5 mg/L - 168.0 mg/L for Eldeniya-East, are obtained for the nitrate content where most of them are beyond the safe level of drinking water, 50 mg/L. The soil pH in all the samples falls within the acidic range, varying from 2.99 - 6.73 in Ihalagama-East and 3.07 – 6.68 in Eldeniya-East.  Most of the soil samples contain high nitrate contents, indicating significant contamination. The percentage soil organic matter content varies between 0.60% and 13.27% in both areas. Many fertile agricultural soils typically have an organic matter content ranging from 3% - 6% revealing that most of the samples are beyond the standard levels. The distribution of water-soluble and extractable cations does not exhibit a wide range. According to the findings, though two Grama Niladhari Divisions are selected, they also display a huge variation. This reveals the importance of mapping to address contaminations, effects of natural disasters which lead to changes in the studied water and soil quality parameters.