FLUVIAL DISTURBANCES IN KARST STREAMS: SEDIMENT TRANSPORT PROCESSES

Because of the perceived constancy of karst environments, the parameters of disturbance frequency and magnitude are critical to understanding the structure and function of karst hyporheic ecosystems. Disturbance processes are credited with maintaining biological diversity in aquatic ecosystems and they include environmental variations such as discharge, sediment transport, and thermal fluxes.

Understanding the ecology of hyporheic zones within karst environments requires investigation of their geomorphology. Fluvial processes in karst streams, however, have been largely unstudied in the past. This research evaluated sediment transport in karst streams and provides insight into a disturbance process that will aid stream ecologists in the integration of hyporheic zone concepts into those of karst aquatic ecosystems

Sediment transport was evaluated in two fluviokarst systems (the Devil’s Icebox, central Missouri, and Carter Caves, eastern Kentucky). Shear stress analysis shows that the 85th-percentile particle can be transported at bankfull stage at all but a few of the 59 stations surveyed. Frequency data indicate that bankfull discharges recur every 1.7 years and smaller discharges capable of entrainment occur as frequently as several times a year.

Integrating the analyses of the sediment transport processes with the results of a concurrent investigation of thermal variation in karst stream substrates allowed disturbance processes in karst hyporheic zones to be evaluated. Based on the frequency of disturbance events, and comparisons to reported values for non-karst systems, biologically-significant levels of disturbance should occur in the investigated systems. The characteristics and mechanisms of these disturbance processes are likely common to most fluviokarst systems.