Source areas and climatic effects in carbonate groundwaters determined by saturation indices and carbon dioxide pressures

A previous study of 14 carbonate springs in Nittany valley in central Pennsylvania showed that the feeder system for the springs could be characterized as conduit flow or diffuse flow on the basis of the variability in water chemistry. Saturation indices and CO 2 partial pressures calculated from the raw data of the previous study were then sorted into monthly groups and averaged. Conduit springwaters are always aggressive with respect to both calcite and dolomite, no seasonal trend being in evidence. The high variability reflects mostly variation in recharge, short residence time, and slow kinetics of equilibration between water and wall rock. Diffuse springwaters are somewhat aggressive with respect to calcite during the growing season but become somewhat supersaturated during the winter. Waters from diffuse‐flow springs in dolomite are nearly at saturation, whereas waters from diffuse‐flow springs in limestone are always undersaturated with respect to dolomite. The equilibrium CO 2 pressures of conduit springwaters show a regular seasonal trend having a pronounced maximum during the growing season. The CO 2 content of diffuse‐flow springs is highly variable, and although the summer maximum is present, the CO 2 content also reflects variations in the CO 2 production in the catchment areas of infiltrating waters.