There are thousands of dams throughout the rivers of the U.S., and they affect two essential aspects of the way rivers work: the natural flow of the river is disrupted, and the connection of upstream-to-downstream habitats are severed, impeding the movement of fish, macroinvertebrates and other aquatic organisms. However, the number of dams that are being decommissioned and removed is accelerating, and once the dam is gone, river channels and their floodplains are being restored to improve water quality, reconnect upstream and downstream habitats, and return the river to a more natural flow regime. Here in Columbus, the 75-year-old 5th Avenue dam on the Olentangy River (pictured above left) was removed in the fall of 2012, clearing the way for the river channel and floodplain to be restored (right next to Ohio Stadium on the OSU campus, see pictures below). We have been following several ecological responses of the river and its restoration after dam removal. One aspect of the river we tracked was the macroinvertebrate community, which is often used as an indicator of water quality.
Check out our new article about how macroinvertebrate communities responded after the 5th Avenue dam was removed:
(2017) Seasonally distinct taxonomic and functional shifts in macroinvertebrate communities following dam removal. PeerJ 5:e3189 https://doi.org/10.7717/peerj.3189
Abstract: Dam removal is an increasingly popular restoration tool, but our understanding of ecological responses to dam removal over time is still in the early stages. We quantified seasonal benthic macroinvertebrate density, taxonomic composition, and functional traits for three years after lowhead dam removal in three reaches of the Olentangy River (Ohio, USA): two upstream of former dam (one restored, one unrestored), and one downstream of former dam. Macroinvertebrate community density, generic richness, and Shannon–Wiener diversity decreased between ∼9 and ∼15 months after dam removal; all three variables consistently increased thereafter. These threshold responses were dependent on reach location: density and richness increased ∼15 months after removal in upstream reaches versus ∼19 months downstream of the former dam. Initial macroinvertebrate density declines were likely related to seasonality or life-history characteristics, but density increased up to 2.27× from year to year in three out of four seasons (late autumn, early spring, summer) across all reaches. Macroinvertebrate community composition was similar among the three reaches, but differed seasonally based on non-metric multidimensional scaling (NMDS) and analysis of similarity (ANOSIM). Seasonal differences among communities tended to decrease after dam removal. We detected community-wide shifts in functional traits such as multivoltinism, depositional habitat use, burrowing, and collector-gatherer feeding mode. We observed that these traits were expressed most strongly with Chironomidae, which was the most abundant family. Our results suggest that seasonal environmental conditions can play a role in the response and recovery of macroinvertebrate communities—often used to monitor ecosystem condition—following dam removal. In particular, macroinvertebrate density and diversity can show recovery after dam removal, especially in seasons when macroinvertebrate density is typically lowest, with concomitant changes to functional trait abundance. Thus, we recommend scientists and managers consider responses to dam removal throughout the year. Further, similar density, generic richness, and functional traits among reaches suggest that channel restoration after dam removal may initially have equivocal effects on invertebrate communities.