Responses of macroinvertebrate communities to small dam removals: implications for bioassessment and restoration

1.Small dam removals are increasing on a global scale; yet general predictions of organism response to dam removal are constrained by heterogeneity of study designs, implementation strategies, geographies, and characteristics of dams and their removals.

2.Macroinvertebrate data extracted from 29 studies including 34 small dam removals over a broad geographical range was re-analysed utilizing dam removal effect sizes (a quantified change from before to after removal). Effect sizes of 10 metrics of community structure were calculated to investigate the spatiotemporal extent of small dam removal effects and if responses differ with characteristics of the dam and environmental settings.

3.We found that dam removal had initial negative effects on total macroinvertebrate density and EPT (Ephemeroptera, Plecoptera, and Trichoptera) density, both downstream and upstream; however recovery to pre-removal values was reached and exceeded after ca 15-20 months. Mean annual discharge, land use ...