Geochemical characteristics of groundwater in different climatic zones of Sri Lanka

Sri Lanka is characterized by well-demarcated climatic zones based on the rainfall pattern known as wet zone, dry zone and intermediate zone. Groundwaters in these three zones are extracted mainly for drinking and irrigation from metamorphic hard rock aquifers and saprolite developed on metamorphic rocks. Detailed hydrogeochemical investigations were carried out covering these three climatic zones in order to characterize the groundwater. A total of 166 groundwater samples were collected representing three climatic zones and analyzed for their major and trace element geochemistry. The results indicate a clear difference in the geochemistry of groundwater between climatic regions, whereas semiarid dry zone groundwater is characterized with higher dissolved mineral contents compared that of the wet and intermediate zones. Low pH levels were noticed in the wet zone areas, while high calcium and fluoride contents were observed in the dry and intermediate terrains. Remarkably, high phosphate contents were observed in all three regions, indicating the influence of fertilizer application on groundwater. Particularly in the dry zone regions, the groundwater chemistry is mainly controlled by rock-water interactions and ion exchange processes in which high mineral contents are added from underlying metamorphic rocks to the drinking and irrigation water. The results indicate that groundwater in the dry zone area is under stress compared to other climate areas, but in the wet zone groundwater shows remarkable influence of anthropogenic activities.