Beaver dams overshadow climate extremes in controlling riparian hydrology and water quality

Hydrologic extremes dominate chemical exports from riparian zones and dictate water quality in major river systems. Yet, changes in land use and ecosystem services 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. Beaver dams increase water flow gradients and nitrate removal far more than seasonal climate extremes. An expanding beaver range is an ecosystem feedback to climate change which could improve water quality.

Automated summary

Beaver dams have a greater impact on water residence time and oxygen and nitrogen fluxes in riparian subsurface than seasonal hydrologic extremes. With climate change, the expanding range of beavers will further alter watershed hydrology and biogeochemistry, illustrating that ecosystem feedbacks to climate change will change water quality in river systems.