Groundwater trace element chemistry of the karstified limestone of Andhra Pradesh, India

Abstract

Groundwater trace element geochemistry was evaluated in the Narji Limestone which possesses a range of substituted trace elements in the mineral matrix. The data indicate three interrelated processes control water–rock interactions and elemental concentrations in this aquifer. Dissolution influenced by pH–Eh, recharge processes and residence time controls Ca2+, Mg2+, Mn, Al, Cd, Ba, Sr, Co, Li, Rb, V, Fe, Pb, As, Si and Cu concentrations, while the weathering of quartzites and shales releases minute quantities of Na+, K+, Cl−, Si and F into groundwater. A significant amount of Na+, K+, Cl−, NO3 −, SO4 2−, Al, Fe, Cd, As, Pb, Ni, Zn, Mn, Sr, Cl, Br, Sb, Ag, Mo, Co and Cu has leached into groundwater from the use of fertilizers/manures and decayed organic matter in cultivated areas. High evapotranspiration has concentrated the chemicals by about 84%. Urbanization, land-use changes, mining and local industries have significantly increased Cd, Se, Ni, Zn, V, Fe, Cd, Sb, Ag and Cr concentrations in groundwater. The composition of groundwater is also affected by sewage, waste disposal and industrial and commercial activities. The chemical properties of about 18% of groundwater samples suggest the role of dissolution/weathering, 46% of samples have been influenced by the effects of evaporation and agricultural activities while 29% of the samples have been affected by natural hydrogeochemical processes and the effects of agricultural and industrial contamination. The quality of groundwater in the area generally conforms to the WHO recommended limits for drinking. Increasing anthropogenic interactions are likely to degrade the groundwater as karst is highly prone to contamination. This demands further investigations to ensure that the groundwater remains suitable for its intended uses in the future.