Divergent Geochemical Pathways of Carbonate Aquifer Evolution in a Classic Karst Terrain: (2) Groundwater Source Delineation Using Regional Water Chemistry Data.

Springs provide ideal monitoring points for groundwater chemistry, which are important for managing groundwater resources. The chemistry of these spring waters aggregate geochemical reactions along the flow path. In this paper, part two of a two-part investigation, 104 perennial springs in the classic karst landscape of the Mitchell Plateau, Indiana, USA were sampled at base flow. Many of these springs are historically important for domestic, agricultural, commercial, and recreational use. Multifactor analysis of field measurements, principal ions, and stable isotopes revealed five primary clusters of springs emerging from the Mitchell Aquifer. Two clusters represented earth-alkaline-type karst groundwater that were discriminated by temperature and inorganic carbon concentration. Two other clusters comprised mineralized alkaline-earth-type groundwater with excess alkalis and elevated sulfate. The fifth cluster appeared to be groundwater that included meteoric and mineralized sources. Using the longitudinal data over two years from part one of this investigation, two mixing lines were used to describe the data set. The mixing lines pointed to sources of sulfur in mineralized springs from deep brines and from evaporite dissolution. Collectively, these regional data allow for a better delineation of water types and differentiation between the Upper and Lower Mitchell Aquifer. [ABSTRACT FROM AUTHOR]