Meta-analysis of the impacts of water management on aquatic communities

Systematic meta-analyses were conducted on the ecological impacts of water management, including effects of (i) dewatering on macroinvertebrates, (ii) a hypolimnetic release on downstream aquatic fish and macro invertebrate communities, and (iii) flow modification on fluvial and habitat generalists. Our meta-analysis indicates, in general, that (i) macroinvertebrate abundance is lower in zones or areas that have been dewatered as a result of water fluctuations or low flows (overall effect size, -1.64; 95% confidence intervals (CIs), -2.51, -0.77), (ii) hypolimnetic draws are associated with reduced abundance of aquatic (fish and macroinvertebrates) communities (overall effect size, -0.84; 95% CIs, -1.38, -0.33) and macroinvertebrates (overall effect size, -0.73; 95% CIs, -1.24, -0.22) downstream of a dam, and (iii) altered flows are associated with reduced abundance of fluvial specialists (-0.42; 95% CIs, -0.81, -0.02) but not habitat generalists (overall effect size, -0.14; 95% CIs, -0.61, 0.32). Publication bias is evident in several of the meta-analyses; however, multiple experiments from a single study may be contributing to this bias. Fail-safe Ns suggest that many (> 100) studies showing positive or no effects of water management on the selected endpoints would be required to qualitatively change the results of the meta-analysis, which in turn suggests that the conclusions are reasonably robust.