November 08, 2022

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Beaver Dams Overshadow Climate Extremes in Controlling Riparian Hydrology and Water Quality

Expanding beaver populations may counteract climate-driven degradation of riverine water quality in the western United States.

Beaver dam on the East River at the Watershed Function Science Focus Area field site in Crested Butte, Colo.

[Reprinted under a Creative Commons Attribution 4.0 International License (CC BY 4.0) from Dewey, C. et al. "Beaver Dams Overshadow Climate Extremes in Controlling Riparian Hydrology and Water Quality." Nature Communications 13 (6509), (2022). DOI:10.1038/s41467-022-34022-0.]

The Science

Warming temperatures and frequent drought are degrading riverine water quality in the western United States. Simultaneously, climatic shifts and changes in ecosystem management are expanding the range of American beavers, whose dams are known to improve riverine water quality. By comparing the water quality impacts of a beaver dam and historically low river levels, which likely represent river levels of a future hotter climate, researchers found that the beaver dam increased removal of reactive nitrogen, a freshwater contaminant, by 44% compared to low river levels. The beaver dam pushed an enormous volume of river water and reactive nitrogen into surrounding soils, where microbial processes converted reactive nitrogen to nitrogen gas, eliminating its potential as a freshwater contaminant and rendering it harmless.

The Impact

Researchers demonstrate that ecosystem feedbacks to climate change, such as expansion of beaver populations, alongside ecosystem management practices, such as legal protections for beavers, can partially reverse detrimental effects of climate change on water quality. By illustrating the interplay between beavers’ ecosystem services, climate change, and water quality, this research informs and supports land and ecosystem policies that aim to address water quality impacts of climate change.

Summary

Scientists monitored hydrologic and geochemical conditions along a reach of Colorado’s East River over multiple years (2018-2019), which captured a historic drought and construction of a beaver dam at this site. Using these field measurements, they developed a reactive transport model to quantify dissolved oxygen and reactive nitrogen fluxes through riparian soils during the drought and construction of the beaver dam (2018), as well as during unusually wet conditions (2019). The model demonstrated that the beaver dam imposed hydraulic gradients across the riparian subsurface which were more than 10 times greater than gradients imposed by low- and high-water conditions. By imposing a steep hydraulic gradient, the beaver dam increased flux of water and nitrate into riparian soils relative to seasonal extremes, where microbial processes converted nitrate to nitrogen gas through denitrification. The overall nitrate flux increase from the beaver dam led to a 44% increase in nitrate removal compared to seasonal extremes. Finally, researchers evaluated the beaver dam’s nitrate removal under a range of denitrification rates, finding that the dam’s relative effects were largely insensitive to microbial process rates.

Principal Investigator

Christian Dewey
Stanford University
cwdewey@stanford.edu

Co-Principal Investigator

Eoin Brodie
Stanford University
elbrodie@lbl.gov

Program Manager

Jennifer Arrigo
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
jennifer.arrigo@science.doe.gov

Funding

This work was supported by the Watershed Function Science Focus Area, which is funded by the Biological and Environmental Research (BER) Program within the U.S. Department of Energy’s (DOE) Office of Science under Award Number DE-AC02-05CH11231. Support was also received from the BER Environmental System Science Program under Project Award Number DE-SC0016544 and DOE Office of Science Graduate Student Research Program. The Rocky Mountain Biological Laboratory in Gothic, Colo., provided field support for this research.

References

Dewey, C., et al. "Beaver Dams Overshadow Climate Extremes in Controlling Riparian Hydrology and Water Quality." Nature Communications 13 6509  (2022). https://doi.org/10.1038/s41467-022-34022-0.