As climate change worsens water quality and threatens ecosystems, the famous dams of beavers may help lessen the damage.
That is the conclusion of a new study [nature.com] by Stanford University scientists and colleagues, publishing Nov. 8 in Nature Communications. The research reveals that when it comes to water quality in mountain watersheds, beaver dams can have a far greater influence than climate-driven, seasonal extremes in precipitation. The wooden barriers raise water levels upstream, diverting water into surrounding soils and secondary waterways, collectively called a riparian zone. These zones act like filters, straining out excess nutrients and contaminants before water re-enters the main channel downstream.
This beneficial influence of the big, bucktoothed, amphibious rodents looks set to grow in the years ahead. Although hotter, arid conditions wrought by climate change will lessen water quality, these same conditions have also contributed to a resurgence of the American beaver in the western United States, and consequently an explosion of dam building.
"As we're getting drier and warmer in the mountain watersheds in the American West, that should lead to water quality degradation," said the study's senior author Scott Fendorf [stanford.edu], a professor of Earth system science at Stanford University. "Yet unbeknownst to us prior to this study, the outsized influence of beaver activity on water quality is a positive counter to climate change."
[...] "Completely by luck, a beaver decided to build a dam at our study site," said Dewey, who is now a postdoctoral scholar at Oregon State University (whose mascot, incidentally, is a beaver). "The construction of this beaver dam afforded us the opportunity to run a great natural experiment."
[...] To understand how beaver dams may affect water quality in a future where global warming produces more frequent droughts and extreme swings in rainfall, the researchers compared water quality along a stretch of the East River during a historically dry year, 2018, to water quality the following year, when water levels were unusually high. They also compared these yearlong datasets to water quality during the nearly three-month period, starting in late July 2018, when the beaver dam blocked the river.
[...] While in place, the beaver dam boosted removal of unwanted nitrogen from the studied East River section by 44% over the seasonal extremes. Nitrogen is an especially pernicious problem for water quality as it promotes overgrowth of algae, which when decomposed starve water of the oxygen needed to support diverse animal life and a healthy ecosystem.
[...] "We would expect climate change to induce hydrological extremes and degradation of water quality during drought periods," said Fendorf, "and in this study, we're seeing that would have indeed been true if it weren't for this other ecological change taking place, which is the beavers, their proliferating dams, and their growing populations."
Dewey, C., Fox, P.M., Bouskill, N.J. et al. Beaver dams overshadow climate extremes in controlling riparian hydrology and water quality. Nat Commun 13, 6509 (2022). DOI: 10.1038/s41467-022-34022-0 [doi.org]