Environment: Beaver dams may maintain river water quality in western USA

Beaver dams may effect river water quality by controlling the river flow and fluxes of nitrogen and oxygen when compared to hydrologic extremes caused by climate, a paper published in Nature Communications suggests. The findings, based on a river course in Colorado, USA, indicate that the expanding range of beavers may help mitigate the negative effects of climate change on water quality in river systems.

Hydrological extremes, such as rapid snowmelt and severe rain events, are known to impact water quality in major river systems. Increasing climate variability, alongside other anthropogenic impacts, is altering hydrologic extremes — with both droughts and flooding becoming more frequent and intense. Additionally, an overall drier, hotter climate in the western US is expanding the range of American beavers, whose dam building efforts are known to affect local water flow and quality.

Scott Fendorf and colleagues monitored the effects of climate-induced hydrological extremes between 2018⁠–2019, both during low water and snowmelt-induced flood periods, in a mountainous watershed of the East river, Colorado, USA, before and after beavers built dams in the area. They found that the hydrologic response of the watershed is impacted by climate change, altering river flows and the export of carbon, nutrients, and contaminants and that beaver dams may mitigate the impacts of this. The authors found that beaver dams increase the hydraulic gradient of the river over 10 times more than seasonal hydrologic extremes. This increases nitrate removal by nearly 50%, relative to seasonal extremes alone, and improves water quality for oxygen-breathing aquatic organisms.

The authors suggest that although climate change is projected to alter seasonal hydrologic extremes, precipitation and temperature patterns, the presence of beaver dams may help mitigate the impacts predicted under future climate conditions and protect downstream water quality.