Intermittent streams support an aquatic community dominated by species that are adapted to cycles of drying and rewetting. For the southeastern US, climate projections along with increasing human water demand may increase the frequency and severity of stream drying. Regionally the prevalence of intermittent stream reaches may expand, and affect species distributions. By increasing the frequency and severity of drying certain longer-lived taxa and those with poor dispersal abilities may be excluded from previously suitable habitat. In an intermittent stream in the Gulf Coastal Plain of southwestern Georgia, we examined invertebrate assemblages before and after a drying event at the end of a severe drought. Invertebrate samples were collected monthly from three reaches across available habitats (rock, wood, sand and organic matter) and identified to the lowest feasible taxonomic level. Traits relating to voltinism and the ability to withstand drying were examined using mixed-effect models in relation to community recovery to identify taxa more susceptible to increased drying. Non-metric multi-dimensional scaling (NMDS) followed by ANOSIM (in R) was used to identify community changes over the time period.
Results/Conclusions
Following flow resumption, we found no significant difference in total abundance or richness compared to pre-drying measures; however, community composition was significantly different over the 96 day recovery period (F=6.1882, df=8, p=0.01). Within 11 days of flow resumption, taxa capable of surviving dry periods were at pre-drying levels and abundance recovered within 36 days mostly comprised of Chironomidae and Simulidae. Multivoltine taxa incapable of surviving drying recovered within 96 days and were largely comprised of Baetidae (Acerpenna and Baetis) and Cheumatopsyche. Finally, those taxa that are most drought sensitive (not desiccant resistant and univoltine) varied in recovery. Some did not reach pre-drying levels during the 96 day sampling period while others returned within 65 days. Identifying life history traits that facilitate resistance and the ability to recolonize will be important in understanding how increased drying will affect regional stream networks. While total richness and abundance recovered within a few weeks of flow resumption, recovery of the pre-drying community took longer depending on the life cycle and adaptations of individual taxa. In future climate scenarios, increasing the frequency and duration of drying could exclude certain taxa from increasingly intermittent stream segments, reducing their population distribution regionally.