In the upper reaches of the Skykomish River in Washington state, a pioneering team of civil engineers is keeping things cool. Relocated beavers increased water storage and lowered stream temperatures, indicating that such schemes can be an effective tool for mitigating some of the effects of climate change.
In just one year after their arrival, the new recruits brought average water temperatures down by about 2 degrees Celsius and raised water levels as much as about 30 centimeters, researchers reported in July. Ecosphere. While scientists have discussed beaver dams as a means of restoring streams and bulking up groundwater, the effects of a large, targeted relocation had been relatively unknown (SN: 26.3.21).
“That water storage is so critical in the drier periods because it’s what can keep the ecosystem resilient to drought and fire,” says Emily Fairfax, an ecohydrologist at California State University Channel Islands in Camarillo who was not involved in the study.
The Skykomish River flows down the west side of Washington’s Cascade Mountains. Climate change is already transforming the region’s hydrology: the snowpack is shrinking, and the snowfall is turning to rain, which drains quickly. The waters are also getting warmer, which is bad news for salmon populations struggling to survive in warm water.
Beavers are known to tinker with hydrology as well (SN: 27.7.18). They build dams, ponds and wetlands, and dredge streams for their caves and cabins (complete with underwater entrances). The dams slow the water, store it upstream longer and cool it as it flows through the ground below.
From 2014 to 2016, aquatic ecologist Benjamin Dittbrenner and colleagues relocated 69 beavers (Castor canadensis) from lowland areas of the state to 13 upstream sites in the Skykomish River basin, some with relict beaver dams and others untouched. Since beavers are family-oriented, the team relocated entire clans to increase the chances that they would stay.
The researchers also matched singletons with potential mates, which seemed to work well: “They weren’t picky at all,” says Dittbrenner, of Northeastern University in Boston. Fresh logs and woodcuts got the beavers started in their new neighborhoods.
At the five sites that saw long-term construction, beavers built 14 dams. Thanks to these dams, the volume of surface water—streams, ponds, wetlands—increased to about 20 times greater than streams without new beaver activity. Meanwhile, underground, wells in three locations showed that after dam construction, the amount of groundwater grew to more than double what was stored on the surface in dams. Stream temperatures downstream of the dams dropped by an average of 2.3 degrees C, while streams not exposed to beaver fixation warmed by 0.8 degrees C. All of these changes occurred within the first year after relocation.
“We’re achieving restoration goals almost immediately, which is really cool,” says Dittbrenner.
Crucially, the dams lowered the temperature enough to almost completely take the streams out of the harmful zone for salmon during a particularly hot summer. “These fish also experience heat waves in the water system, and the beavers protect them from that,” says Fairfax. – It was big for me.
The study also found that small, shallow abandoned beaver ponds were actually warming streams, perhaps because the cooling system had broken down over time. Targeting these ponds as potential relocation sites may be the most effective way to bring temperatures down, the researchers say. When displaced populations establish and breed, young beavers that leave their homes may seek the abandoned sites first, Dittbrenner says, since it uses less energy than starting from scratch. “If they find a relic pond, it’s game on.”