Effects of beaver activity and beaver dam analogs on water quality and macroinvertebrate diversity in urban streams

Background/Question/Methods

Beaver populations are rebounding throughout the US and seem well adapted to living in urban streams. By retaining stormwater and sediment, increasing microbial processing, and returning stream channels towards pre-colonial geomorphology, beaver dams could improve water quality and habitat in impacted urban streams. Beaver dam analogs (BDAs) are a human attempt to use beaver dams as a model of process-based restoration in locations not currently colonized by beavers. If they work similarly to natural beaver dams, they could prove to be useful, less expensive, and less impactful than traditional form-based restoration. In Atlanta, GA, USA, we sampled stream macroinvertebrates in 2018 and 2021 upstream and downstream of urban beaver dams and BDAs, which were installed in 2020. We also sampled stream water chemistry monthly 2017-2021 upstream and downstream at the same sites and additional beaver sites.

Results/Conclusions

We found some positive changes in the macroinvertebrate community following the BDA installation, but the beaver dam site had declined in both abundance and diversity. The water quality trends at all sites were complicated, with some indications of improved downstream water quality, in particular nitrogen retention, but these trends were also affected by hydrology, in particular large, dam-removing storm events, a common occurrence for urban beavers that decreases the water quality benefits of beavers seen in less hydrologically impacted systems.