Ground Water Quality in Mahakanumulla and Thirapane Tank Cascades in the Dry Zone of Sri Lanka

Abstract

Many people in the world are depending on the ground water as their source for domestic and agricultural activities. Ground water is an extremely valuable resource and pollution of ground water resources is a matter of serious concern. Twelve dug wells under six tanks (Siwalagala, Amanakkatuwa, Mahakanumulla in Mahakanumulla cascade and Meegasagama, Alisthana and Thirappane in Thirappane cascade) were selected for this study. Sampling had been carried out for two years from February 2010 to January 2012. Water samples were collected monthly intervals from dug wells. In all water samples, major plant nutrients viz. dissolved nitrate (N03) phosphate (P043) potassium (K*) and toxic elements; cadmium (Cdt2), and fluoride (F) were determined using standard laboratory techniques. N03 concentration of dug wells varied from 2.10 - 10.51 mg/ Land in this study, There is a moderate positive correlation between tank water N03 and dug well N03 ( r = 0.536). P043 concentration ranged from 0.003 - 0.46 mg/ L and K* concentration varies from 1.03 - 8.50 mg/ L .The most health detrimental element Cd‘2 which enters to water through phosphate fertilizer and organic manure also showed the significant temporal variation throughout study period. It varies from 0.001- 0.02 mg/ L and exceeded the permissible level of drinking water which is 0.003 mg/ L (WHO, 2004). Fluoride which has both beneficial and detrimental effect on human health varies from 0.49-2.39 mg/ L. In this analysis, all major nutrients and toxic elements (Cd and F) showed relatively high concentrations during the rainy season where the low concentrations were recorded in dry season. The highest concentration of plant nutrients and toxic elements occurred in ground water during the months of October, November, April, May and June, which are the months that farmers apply chemical fertilizers to croplands. It is evident from the results that major plant nutrients and toxic elements in ground water varied significantly with the bimodal rainfall, cropping seasons and fertilizer use. None of the nutrients exceeded permissible level for drinking water except Cadmium.