Beavers Mitigate Global Warming

Beavers provide a natural feedback that protects
water quality downstream, scientists find

The protection of water quality by beaver dams is much greater than the protection offered by seasonal extremes in river flow. And as global warming grows, there will be more beavers to build more dams, expanding the beneficial feedback effect.

Beaver dams overshadow climate extremes in controlling riparian hydrology and water quality (Dewey et al., Nature Communications, 8 November 2022).

This surprising paper explores a natural feedback system that compensates for rising temperatures in the climate. Led by Scott Fendorf of Stanford University, a team measured the flow of nitrate pollutants downstream during wet and dry seasons at the East River near Crested Butte, Colorado, a location where meanders invite beavers to build their dams. They made measurements before a beaver dam was built, during its operation, and after it collapsed. The measurements were surprising: the beaver dams increased the hydraulic gradient by 10 to 13 times, resulting in nitrate removal 44% greater than climatic factors alone.

Hydrologic extremes [i.e., wet and dry periods] dominate chemical exports from riparian zones and dictate water quality in major river systems. Yet, changes in land use and ecosystem services [e.g., by beaver dams] alongside growing climate variability are altering hydrologic extremes and their coupled impacts on riverine water quality. In the western U.S., warming temperatures and intensified aridification are increasingly paired with the expanding range of the American beaver—and their dams, which transform hydrologic and biogeochemical cycles in riparian systems. Here, we show that beaver dams overshadow climatic hydrologic extremes in their effects on water residence time and oxygen and nitrogen fluxes in the riparian subsurface. In a mountainous watershed in Colorado, U.S.A., we find that the increase in riparian hydraulic gradients imposed by a beaver dam is 10.7–13.3 times greater than seasonal hydrologic extremes. The massive hydraulic gradient increases hyporheic nitrate removal by 44.2% relative to seasonal extremes alone. A drier, hotter climate in the western U.S. will further expand the range of beavers and magnify their impacts on watershed hydrology and biogeochemistry, illustrating that ecosystem feedbacks to climate change will alter water quality in river systems.

Beavers cannot reduce global warming itself, of course. They are just limiting the damage of nitrate pollutants reaching downstream water supplies with their dams. It’s amazing that this natural feedback system is compensating for climate change, however. It’s a factor that climate modelers didn’t consider.

Due to the extreme hydrologic conditions that beaver dams impose, it is probable that beaver dams will overshadow future climate extremes in controlling exports of reactive N from mountain riparian zones. Growing beaver populations are likely to lead to greater hyporheic nitrate removal and reduced nitrate loading to downstream watersheds, potentially protecting freshwater quality. Our findings indicate that the impacts of beaver dams dwarf the direct hydrologic impacts of warming temperature and increased aridification, which decrease snowpack and peak discharge, on riparian water quality in mountain watersheds. As future impacts of climate change on river hydrology and water quality are assessed, feedbacks from ecosystem changes, including those induced by management, need to be included.

What other natural feedbacks from biological “ecosystem services” need to be included in climate models?

Meanders on the East River, Colorado, near where the scientists measured the effects of beaver dams.

Other Beaver Benefits

Beavers can do wonders for nature – but we should be realistic about these benefits extending to people (The Conversation, 26 Sept 2022). Three biologists from English universities (Joshua and Annegret Larson and Matthew Dennis) also talked about the wonders that beavers do for nature.

The beaver is a unique ecosystem engineer that can create a landscape that would otherwise not exist, thanks to the animal’s ability to build dams. As we experience more frequent heatwaves and drought, the potential role of beavers in safeguarding against these risks has captured widespread attention.

Beaver habitats are claimed to lower local stream and air temperatures, and by maintaining water supplies, provide insurance against drought. Greater water storage may also improve the resilience of a landscape towards wildfire.

These authors wrote their article over a month before the Stanford study was published. They caution, however, that beavers cannot save humanity from climate change.

However, it is important to consider the significance of beaver habitats as a solution to our changing climate from both human and wildlife perspectives. It’s not as simple as saying beavers can protect human society against the effects of extreme weather.

The impacts of the beaver are complex: their ponds lower local temperatures, but they also open tree canopies to sunshine. There will never be enough beaver dams to store the water needs of society in a warming climate, nor can they prevent all wildfires. That being understood, the authors still appreciate all that beavers do for nature.

However, it would be wise to temper expectations for the role of beavers as a drought solution for human settlements. Nevertheless, by offering a local buffer against the ravages of drought, heatwaves, and wildfire, beaver habitats carry the potential to help stimulate nature recovery and reverse biodiversity loss.

A simple 45-second animated video in the article illustrates how a beaver transforms its landscape and creates a new ecosystem.

One beaver dam can impound a lot of water. Photo by David Coppedge, Lundy Canyon, California.