Advances in monitoring to understand flow paths in karst: Comparison of historic and recent data from the valley and ridge of Pennsylvania

Abstract

We revisited seven karst springs studied in 1971 to examine how advances in monitoring techniques influence our understanding of spring flow paths and recharge. These springs in the Valley and Ridge of Pennsylvania offer a variety of spring discharge volumes and physical appearance (visible conduits at the discharge site versus fracture networks). We focused on temperature for a comparison between historic and recent trends because it is the least likely to differ in value due to updated measurement techniques. High-resolution temperature data showed variations in storm responses (not observed with historic data) which distinguish among springs. We also used automatic samplers to track geochemical changes during storm events. Variations in CO2 concentrations and Mg/Ca ratios provided indicators of fast and slow recharge and changes in flow paths over time. Some springs showed similar response from storm to storm and some varied. Rare earth elements (REEs) were analyzed in baseflow samples to evaluate their potential for distinguishing spring source rock along flow pathways. The REE grouped springs differently than their temperature and storm response geochemistry. This study showed that classification of karst springs varied depending on the parameter monitored. This variation further points out the complexity of karst flow paths and recharge. Multiple methods and long-term monitoring are needed to interpret karst spring discharge and provide sampling schemes for source water protection.