Evaluation of single- and multi-metric benthic macroinvertebrate indicators of catchment disturbance over time at the Fort Benning Military Installation, Georgia, USA

Stream benthic macroinvertebrates are useful indicators of the impacts of disturbances on catchment and stream conditions because they integrate many catchment-scale ecological processes. We tested the ability of macroinvertebrate assemblages over a 3-year period to indicate the impacts of a range of disturbances resulting from military training at the Fort Benning Military Installation, Georgia. We studied seven small streams that drained catchments spanning disturbances that ranged from light infantry movements to heavy disturbances from tracked vehicle movements. The main disturbance to streams was influx of sediment associated with training and use of unpaved roads. We quantified disturbance level as the % of catchment occurring as bare ground on slopes >3% and as unpaved road cover. Disturbance level values ranged from about 3 to 15%. Nonmetric multidimensional scaling ordinations revealed macroinvertebrate assemblages were associated with catchment disturbance. Irrespective of season, several richness measures (e.g., number of Ephemeroptera, Plecoptera, and Trichoptera taxa and richness of Chironomidae) negatively corresponded with catchment disturbance, however except for chironomid richness all measures showed high variation among seasons and annually. Compositional and functional feeding group measures also showed high seasonal and annual variation, with only the % of macroinvertebrates clinging to benthic habitats (=% clingers) corresponding with disturbance. Both tolerance metrics tested, the Florida index and North Carolina biotic index, showed little seasonal and annual variation, however only the Florida index related to disturbance. A regional multimetric, the Georgia stream condition index, consistently corresponded with catchment disturbance and showed the least temporal variability. Our results further suggest a threshold at 8–10% of the catchment as bare ground and unpaved road cover, a disturbance threshold similar to that reported for other land uses.