VARIATIONS IN THE TIMING OF KARST SPRING RESPONSE TO STORM FLOW IN TERMS OF SUSPENDED SEDIMENT AND CHEMISTRY

Suspended sediment fluxes through springs interest us for two primary reasons. They are vectors for contaminant transport and potentially a way to determine transport pathways behind a spring mouth. Few studies have attempted to quantify the timing and nature of suspended sediment transport in different karst aquifers under a variety of conditions. To remedy this, monitoring of three springs in Pennsylvania documents the suspended sediment response in each spring during storm flows. Monitoring consists of automatic samplers collecting water samples in response to an increase in water level, and data logging of conductivity, temperature, stage, and turbidity at 15- to 20-minute intervals. The three springs, in ascending order of size Bushkill Spring, Nolte Spring, and Arch Spring, differ from each other in response to storm events, and each spring shows different behavior and response time based on the type of precipitation event.

Data from Arch show that the chemical response of the spring in terms of conductivity does not match the timing and pattern of the sediment response. The sediment pulse lasts several hours while the conductivity effect persists longer and has a more complicated pattern with a sharp initial rise and fall and a longer gradual recovery. Bushkill also shows different timing in sediment and chemical response, though the two springs have different arrival times. Time lags between precipitation and Bushkill sediment concentration peaks can vary by more than five hours when similar size storms occur under dissimilar conditions. Different storms appear to activate different transport pathways for water and sediment. Nolte differs from the other springs in that new sediment laden water takes up to a day to reach the spring.

Preliminary work indicates that the notion of a single characteristic lag time for a spring may be a flawed idea. The size of the spring alone does not predict the behavior of sediment and chemistry without consideration of the storm type and season. Additional storms at each site and further characterization of the sediment should yield additional information on the timing and character of sediment flows. This work should ultimately provide insight into whether travel times and pathways in the spring system can be gleaned from the sediment output and chemistry at the spring.