Recovery of aquatic macroinvertebrate communities from drought in Georgia Piedmont headwater streams

Drought is an important disturbance in stream ecosystems. From 1998-2002 Georgia suffered a major drought, causing many headwater streams to experience reduced flows or to dry completely. Six headwater streams in the Georgia Piedmont were selected and paired based on similarities in substrate structure (sand, bedrock or gravel substrate). Each pair consisted of a stream that dried completely during the drought and one that retained at least some surface water. Riffles were sampled with a core sampler, runs and pools were sampled with a Hess sampler and wood was sampled by randomly collecting pieces of at least 1 cm diameter. Samples were collected within 15 d of reflooding, then after 45, 75, 165, 255, 345 and 435 d. Cluster analyses were used to assess the relative effects of drought history (dried or residual water), stream condition and temporal change. In terms of drought recovery, all streams followed the same pattern of recovery, with a rapid recolonization period following the onset of surface flow. Community compositions were initially similar in most streams, but after 15 d each stream began to develop unique recovery patterns. The number of new taxa colonizing these streams began to level off around 165 d after rewetting. Neither the presence nor absence of residual water nor substrate composition appeared to significantly influence drought recovery patterns of invertebrates.