Relationships between surface water abstraction and aquatic macroinvertebrates

The abstraction of surface water from rivers to meet human demands is widespread and predicted to increase in extent and intensity in the future. Indeed, the combined impact of increasing abstraction and climate change is one of the greatest threats to river ecosystems. Therefore, it is important to understand how rivers respond to increasing magnitudes of abstraction as well as other aspects of abstraction including duration, season, and river condition. I conducted a meta-analysis on the relationships between abstraction and macroinvertebrates to examine 1) the strength and shape of the relationship with increasing abstraction magnitude, 2) the relationship with abstraction duration, 3) whether season influenced the relationship, 4) whether river condition influenced the relationship, and 5) whether small-scale experimental abstraction had similar relationships with macroinvertebrates as larger-scale institutional abstraction. Abstraction magnitude was negatively associated with 3 of 6 macroinvertebrate metrics. Increasing duration of abstraction was related to decreased Ephemeroptera, Plecoptera, and Trichoptera density and drift concentration. Most studies examined abstraction during the summer, making it difficult to compare seasonal effects of abstraction except for its effects on benthic density, for which there was no difference between spring and summer. There was also no effect of river condition on macroinvertebrate responses to abstraction. Finally, small-scale experimental studies generated a different relationship of abstraction magnitude on Diptera density than larger-scale studies, calling into question the usefulness of small-scale experimental studies. Although there were some generalities in the response of macroinvertebrates to abstraction, there was variability in both the strength and direction of response among studies. This finding suggests that it will be difficult to develop prescriptive rules regarding the amount, duration, and timing of abstraction that provides water for human uses but has little impact on river ecosystems. Further work should explore whether rivers with similar attributes (e.g., size, ecoregion, climate) respond to abstraction in similar fashions. In addition, there is a great need to explore the mechanistic factors driving the response of biota to abstraction.