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

Abstract

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.

Quantifying hydrological responses to monsoon‐controlled precipitation across the soil‐groundwater‐stream continuum with long‐term high‐frequency hydrometric monitoring

“…Water levels responded to precipitation inputs in most rainfall events, though rise magnitude and intensity of groundwater level were far larger than those of stream stage (Figures 3b, 6, S1 and Table 2), hampered by the nearby dam (Dewey et al, 2022; Dott et al, 2022; Lu & Chua, 2021). Initial response activation threshold (Rt and Ti) for stream water and groundwater were small compared with soil moisture responses, especially in the groundwater during heavy rainstorms with large TP and rainfall intensity (Figures 5, 7a).…”

Mountainous Floodplain Connectivity in Response to Hydrological Transitions

“…The activity of beavers is widely associated with the enhancement of key riparian zone functions (Larsen et al., 2021), including water storage (Westbrook et al., 2006), fire suppression (Fairfax & Whittle, 2020), flood mitigation (Graham et al., 2022), and enhanced biodiversity (Jordan & Fairfax, 2022). Beaver dams may also help mitigate nitrogen loading of surface waters by increasing their connectivity to riparian sediments where nitrate can be reduced (Dewey et al., 2022). However, beavers alter the hydrology of river corridors in complex ways that may change the water balance through increased evapotranspiration and impact water quality due to increased stream temperatures and metal release (Briggs et al., 2019; Grudzinski et al., 2022).…”

Catchment concentration–discharge relationships across temporal scales: A review

“…Biological regulation of Q occurs primarily via transpiration, altering the timing and amount of water reaching streams on daily, seasonal, and inter‐annual time scales (Flewelling et al, 2014; Ward et al, 2019). Animal‐mediated impacts on Q include flow alteration by beaver dams (Dewey et al, 2022; Majerova et al, 2015) and cascading ecological effects of predator–prey interactions (e.g., wolf reintroduction; Beschta & Ripple, 2019), while animal‐mediated impacts on C include the influence of top‐down controls within stream food webs that lead to algal growth limitation by grazers, altering nutrient uptake (Mulholland et al, 1983).…”