251 Something for Everybody: The Many Faces of Karst Science in all its Multidisciplinary Glory (Posters)

Tuesday, 27 September 2016
9:00 AM - 6:30 PM
Exhibit Hall E/F

CO2 STORM HYSTERESIS IN KARST SPRINGS

Paper number: 251-7
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Studying how the chemistry of karst spring water reacts to periods of increased discharge can provide insights into how these systems store and transmit water. Changes in the partial pressure of carbon dioxide (PCO2) in karst spring water during storm events, in combination with cation analysis, is helpful in discriminating soil water, epikarst water, point recharge storm event water, and matrix water during storm events. Comparing arrival times of these source waters can be used to infer recharge and flow patterns within karst systems.

Direct, prolonged, high frequency field PCO2 data is difficult to acquire and CO2 degassing from automatically-collected storm samples inhibits meaningful PCO2 measurements. To assess CO2 in storm samples, PCO2 values are calculated through solution modeling in PHREEQc using alkalinity measurements, temperature, ion, and pH data. Storm events were captured at Springhouse Spring and Smullton Sinks, located in Centre County, PA, under both dry and wet antecedent conditions. Under dry antecedent conditions, Springhouse Spring exhibited stable Mg/Ca and PCO2 values throughout the storm response. This indicates that unmixed recharge in small- to medium-sized storm events did not reach the spring. This is in contrast to other events at the spring during wet periods which exhibit hysteresis in Mg/Ca ratios. Clockwise Mg/Ca hysteresis was observed in storm samples taken from Smullton Sinks, over the course of a rain event, with an initial rise in Mg/Ca, suggesting matrix flushing (piston flow). The same storm event exhibited counterclockwise PCO2 hysteresis. PCO2 data support the piston flow interpretation with low PCO2 matrix water arriving at the spring first, followed by high PCO2 soil/epikarst water.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-285299

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