Deciphering the inland salinity of a semi-arid area in North Karnataka

This study aimed at understanding the reason(s) behind saline groundwater of the study area. Groundwater samples (n = 21) were collected in both Pre-Monsoon and Post-Monsoon seasons from abstraction structures tapping the shallow, unconfined aquifer throughout the study area. Dataset of chemical analyses was utilized to compute Schoeller indices, Gibbs ratios, various inter-ionic ratios viz. non-isotopic approach for narrowing down the source(s) of Sodium and Chloride ions that are dominant amongst cations and anions respectively. Hydrochemical dataset reveals that rock-water interaction dominates the hydrochemical processes and sodium ions have arisen from silicate weathering, mainly Albite plagioclase mineral whereas Chloride ion was a result of weathering of non-Halite, Plagioclase mineral rich rock source. Secondary geochemical data of fluvial sediments was also utilized to understand the parent rock chemistry and alteration of minerals responsible for groundwater salinity. Four indices, namely Plagioclase Index of Alteration, Chemical Index of Alteration, Index of Compositional Variation and K ₂ O/Al ₂ O ₃ ratio were utilized for secondary dataset that reveal initial and moderate alteration of Plagioclase minerals in addition presence of rock forming minerals in parent source and pre-dominance of clay minerals in soil respectively. The dissolved salts in groundwater of the study area have arisen as a result of semi-arid climate, prolonged rock-water interaction and cation exchange processes between aquifer rock(s) and groundwater.