DISTURBANCE IN SPRING-RUN AND SUBTERRANEAN ECOSYSTEMS

Disturbance has a central role in the structure and function of stream ecosystems. Disturbance is defined as an event that results in death or dispersal of individuals within an ecosystem. In stream ecology, research has focused on the role of flooding as a natural disturbance, although changes in geochemistry and temperature of the water can also cause disturbance.

In surface streams, floods have been found to profoundly affect stream biota particularly when the streambed is mobilized during a scour disturbance. Few studies have focused on spring-run or on subterranean ecosystems where unique and in some cases endemic species reside. In southern Missouri, spring runs are the habitat of the Ozark hellbender (Cryptobranchus alleganiensis bishopi) that prefers a stable thermal and geochemical habitat. In subterranean ecosystems, there is a high percentage of endemic species, such as the pink planaria (Macrocotyla glandulosa Hyman) and Illinois cave amphipods (Gammarus Acherondytes Hubricht and Mackin). The objectives of this study were to determine the frequency of scour, thermal, and geochemical disturbance events in aspring-run and in two subterranean ecosystems.

For spring-run and two subterranean ecosystems, the stability of streambed sediment was assessed by comparing basal shear stress (stage) to critical shear stress (particle diameter). Based on a twenty-eight month record of stream stage and Wolman cobble counts near the gaging stations, scour disturbance events occurred annually for the subterranean ecosystems. For the spring-run ecosystem, scour disturbance events occurred every six months over a three-year period. Geochemical and thermal disturbances as recorded by dataloggers occurred with each and every storm event that occurred over the period of the records, on average every two weeks. Comparing the timing and frequency of disturbance processes, particularly scour disturbance, to the timing and frequency of the reproductive cycles of the animals will provide insight into the poorly known life histories of these animals.