COMPARISON OF STORM BEHAVIOR IN THREE KARST SPRINGS

Storms create stresses on karst systems that allow us to observe threshold behaviors. These thresholds provide clues to the complex pathways that occur in karst through conduits, fractures, and the matrix. We sampled three different karst springs during storms using data loggers for conductivity and water level, and stormwater samplers for water quality and suspended sediment. The three springs have substantially different baseflows: Arch Spring approximately 200 L/s, Nolte Spring approximately 40 L/s, and Bushkill Spring approximately 3 L/s. The springs are located in Paleozoic carbonates of central and eastern PA.

The largest spring had the most predictable variation in conductivity and highly variable suspended sediment load (10 to 30 mg/L with multiple peaks). The middle size spring had considerable variation in conductivity response and the lowest suspended sediment load, less than 10 mg/L during storms. The smallest spring had predictable conductivity but varied in the timing and concentration of suspended sediment (on the order of 10 mg/L to 50 mg/L). The stormwater pathways do not seem to be constant from spring to spring or from storm to storm. Master conduit systems appear to have well integrated pathways and so give the same chemical response to a variety of storms while smaller springs with less well integrated conduit systems seem to have alternate pathways which respond differently depending on storm magnitude, distribution across the recharge area, and antecedent conditions.