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SIMULTANEOUS FLUORESCENT DYE, CONDUCTIVITY AND THERMAL TRACES IN A KARST SPRINGSHED
Data logging of water level, temperature and conductivity show significant event-scale variability following recharge events, with discharge sometimes increasing by an order of magnitude. Temperature may show event-scale minimums or maximums depending on recharge temperature, indicating ineffective heat exchange along the flow system during these intervals. Minimums in conductivity occur because of relatively dilute recharge water. Following recharge events, it may take hours to weeks for each of these parameters to return to pre-event conditions. Outside of recharge periods, these parameters show smaller, cryptic fluctuations.
A springshed or karst groundwater basin delineation for Freiheit Spring is currently underway. To date two positive traces have reached the spring. Uranine injected in an ephemeral sinking stream 1.3 km southwest of the spring was recovered at the spring. Sulforhodamine B was recovered at the spring after it was injected into a sinkhole (MN23:A2631) about 100 m south of the spring.
Temperature and conductivity traces were conducted on 2 July 2009 in conjunction with the Sulforhodamine B dye trace. A pool containing approximately 4,500 liters of water was filled several days before the trace so the water would heat up above groundwater temperature. In addition to the Sulforhodamine B, NaCl and NaBr were added to the pool to increase its conductivity. When the pool was emptied into the sinkhole its temperature and conductivity were 6.3°C and 1.55 mS/cm higher than the spring water. 0.17°C temperature and 0.144 mS/cm conductivity pulses were detected at the spring. Water temperature reacted along the flow path and peaked later than conductivity at the spring. Water conductivity was more conservative, illustrating that heat and solute transport operate under different processes. Information from this trace can provide geometrical properties along the flow system.