Seasonal disturbance of a lake outlet benthic community

Abstract

Disturbance has both evolutionary (as part of the habitat templet) and ecological implications (as a reset mechanism of community succession) for ecosystem processes. The hierarchical nature and seasonality of stream ecosystems suggests a strong system specific response to ecological disturbance. We tested this idea experimentally by disturbing the substratum along a series of transects in a lake outlet during summer, spring, and winter. Our results showed a strong influence of season on the recovery dynamics of the benthic community. Disturbance reduced periphyton biomass only in winter and spring. No disturbance affect was found in summer when algal biomass remained at low levels because of a dense riparian canopy that attenuated solar radiation. In winter and spring, periphyton attained high standing crops only in the absence of disturbance. Benthic organic matter recovered within 30 days regardless of season, primarily due to the rapid accumulation of coarse particulate organic matter. A seasonal response to disturbance also was reflected in the macroinvertebrate community. We found no affects of disturbance on macroinvertebrate densities or species richness in summer, but significant affects on these parameters in winter and spring. The seasonal response in macroinvertebrate parameters corresponded to structural changes in periphyton biomass, and also reflected macroinvertebrate life histories. The results suggest that the recovery of macroinvertebrate communities from physical disturbance is primarily a function of changes in habitat conditions and seasonal shifts in life history.