Multiple stress response of lowland stream benthic macroinvertebrates is dependent on habitat type

Summary

Worldwide, lowland stream ecosystems are exposed to multiple anthropogenic stress due to the combination of water scarcity, eutrophication and fine sedimentation. The understanding of the effects of such multiple stress on stream benthic macroinvertebrates has been growing in the recent years. However, the interdependence between multiple stress and stream habitat characteristics has received little attention, although single stressor studies indicate that it may be decisive in shaping the macroinvertebrate response. We conducted an experiment in large outdoor flumes to assess the effects of low flow, fine sedimentation, and nutrient enrichment on the structure of the benthic macroinvertebrate community and how the response varied in riffle and run habitats of lowland streams. We found a negative effect of low flow on the macroinvertebrate abundance for most taxa in the riffle habitat, an effect which was reduced by fine sedimentation for the dominant shredder species (Gammarus pulex) and by nutrient enrichment for the dominating grazer species (Baetis rhodani). In contrast, fine sediment in combination with low flow rapidly affected macroinvertebrate composition in the run habitat, with decreasing abundances for many species. We conclude that the effects of typical multiple stressor scenarios on lowland stream benthic macroinvertebrates are highly dependent on habitat conditions, and that a high habitat diversity need priority if the resilience of the stream macroinvertebrate community to multiple stress should be maximized.