Data from: 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 in the catchment, and distance from the dam affected the magnitude and
direction of responses of four community metrics: total density, EPT
density, %EPT density, and Family Biotic Index. 4.Synthesis and
applications. Our study provides evidence that macroinvertebrate community
recovery from dam removal is mediated by catchment characteristics and
system size, which may correlate with sediment flushing efficiency.
Negative impacts were observed in smaller systems or those with a high
percentage of undisturbed catchment areas, conditions that may benefit
from sediment management prior to dam removal. Significant responses in
reaches upstream of the impoundment clearly indicate that caution be
applied to interpretations of response in sampling designs that utilize
upstream sites for reference condition.