Dam Removal

Navigating boundaries after dam removal

The theme for the 2018 Society for Freshwater Science meeting in Detroit, MI was “navigating boundaries in freshwater science”. A strong contingent of STRIVE lab members presented research that fit well within this theme, ranging from nutrient dynamics in linked reservoir-stream systems (K. Stefanik, R. Czaja), ecological networks (T. Kenly), upstream-downstream connections driven by aquatic insect drift (L. Rieck), urbanization effects on fish (L. Bajakian), cross-boundary effects of invasive species (K. Diesburg), and water quality and aerial insectivorous birds (J. Corra, D. Manning). Congrats to all for a successful and productive meeting! Check out the STRIVE lab twitter feed for action photos and more!

Speaking of navigating boundaries – we are continuing to learn more about the 5th Ave dam removal and how the Olentangy River ecosystem is responding to the removal of this conspicuous upstream-downstream boundary. Our work (and several other dam-removal studies) has previously focused on the importance of restoring upstream-downstream connections within the stream channel (see our blog post from last year, as well as recent article by Cook and Sullivan, below). But, we wanted to know more about how removing the dam could have effects that cross from the river to the riparian zones directly adjacent to the stream channel. To figure this out, we measured a few key responses: one was the number and biomass of aquatic insects that emerged from the river, and another was the spiders and birds (tree swallows) that live near the river and rely on aquatic insects for food. We also measured the chemical signatures (stable isotopes) of the algae and detritus in the river, the emergent insects, and spiders and swallows; these signatures allowed us to piece together the diets of spiders and swallows to understand how much of their food comes from the river, vs. terrestrial sources.

An orb-weaving spider of the family Tetragnathidae. These spiders often live in the margins of rivers, eating emerging aquatic insects. After dam removal, we observed a nearly 10-fold decline in their densities adjacent to the river. Photo: A. Kautza

So what happened to the river after dam removal that crossed aquatic-terrestrial boundaries? Well, mostly we found that the contraction of the river channel, and loss of vegetation at the edge of the river channel was bad news for the spiders (pictured left) – we saw close to a 10-fold decline in spider densities after the dam was removed, particularly where there was extensive floodplain restoration (pictured below).

The other responses we measured were less clear. By and large, spider and swallow diets were unchanged post-dam removal, and the variation we did observe was explained more by regional factors like annual temperatures, precipitation, and the river’s discharge. Nevertheless, we think that navigating across boundaries in this way could be an important aspect of future dam-removal monitoring and restoration efforts, particularly for larger dam-removal projects that prompt drastic changes to river morphology, and functioning.

Looking upstream toward Lane Avenue during extensive riparian restoration of the Olentangy River a few months after dam removal. Photo: SMP Sullivan

For more information, you can read the paper (open access) online:

Sullivan, S. M. P., D. W. P. Manning, and R. P. Davis. 2018. Do the ecological effects of dam removal extend across the aquatic-terrestrial boundary? Ecosphere 9(4):e02180 DOI:10.1002/ecs2.2180.

On the topic of dam removal, also check out another recent paper (also open access) from STRIVE on the ecological effects of dam removal:

Cook, D.R., and S.M.P. Sullivan. 2018. Associations between riffle development and benthic macroinvertebrate and fish assemblages following lowhead dam removal. Environmental Monitoring and Assessment 190: 339.

 

Tracking seasonal responses of macroinvertebrate communities after dam removal

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:

Sullivan SMP, Manning DWP. (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.