Observations of Hot Moments of Beaver-Driven Biogeochemical Activity in a Mountainous Floodplain Using In Situ Sensors

Authors

Zach Perzan¹* (zperzan@stanford.edu), Tristan Babey^1,2, Sam Pierce², Lijing Wang¹, Brian Rogers¹, Kristin Boye², Kate Maher¹

Institutions

¹Stanford University, Stanford, CA; ²SLAC National Accelerator Laboratory, Menlo Park, CA

URLs

• https://sites.slac.stanford.edu/bargargroup/

Abstract

In many mountainous watersheds, warming temperatures and declining snowpack have led to reduced river flow through the late summer and early fall, decreasing the volume of water available for agriculture, energy, recreation, and human consumption. However, in many regions, warming temperatures also coincide with an expansion in populations of the North American beaver (Cercis canadensis). As ecosystem engineers, beavers build dams that increase seasonal floodplain storage and that may support late-season, groundwater-fed baseflow. These hydrologic changes can also alter biogeochemical cycles within the floodplain, impacting floodplain greenhouse gas release and the export of nutrients and contaminants to surface water. In particular, sudden pulses of biogeochemical activity associated with beaver dam construction (or failure) remain poorly characterized, largely because these transient events are difficult to observe via manual sampling.

To address this gap, researchers instrumented a beaver-impacted floodplain along the Slate River, CO, with an array of in situ sensors monitoring water content, dissolved oxygen concentrations and carbon dioxide concentrations within fine-grained sediments. Construction of a new beaver dam in 2018 inundated portions of the floodplain and coincided with the onset of anoxic conditions in the floodplain sediments. Then, in 2021, migration of the river channel cut off the beaver dam from the main river, causing a large (20 m x 50 m) pond behind the dam to drain and allowing oxygen incursion into previously anoxic sediments. The large pond then refilled in less than 2 hours during a fall rainstorm, returning the floodplain sediments to anoxia once again. With the frequent cycling between oxic and anoxic conditions, these transient events induce pulses of biogeochemical activity that impact water quality in the adjacent river, further highlighting beavers’ impact on ecosystem function.