Short-term dynamics of beaver dam flow states.

Beavers (Castor canadensis and C. fiber) build dams that modify catchment and pond water balances, and it has been suggested that they can be a nature-based solution for reducing flood hydrographs, enhancing low flow hydrographs and restoring hydrological functioning of degraded streams. How water moves through a beaver dam is determined by its flow state (e.g., overflow, underflow). However, current conceptual models only consider flow state as changing over the beaver site occupation-abandonment cycle. To assess whether flow state changes at shorter timescales and identify possible triggers (e.g., rainfall, animals), we integrated camera trap imagery, machine learning, water level measurements, and hydrometeorological data at beaver dams in a montane peatland in the Canadian Rocky Mountains. Contrary to current models, we found that flow states changed frequently, changing a maximum 12 times during the 139-day study period, but that changes had limited synchronicity amongst the dams in the same stream. More than two-thirds of the changes coincided with rainfall events. We observed no changes in flow state in response to beaver activity or wildlife crossings perhaps due to the camera positioning. Our findings augment the long-term oriented framework, which links changes to the occupancy cycle of a beaver pond and frequent and hydrological-driven changes. To develop realistic predictions of hydrological impacts of beaver dams, ecohydrological models should update their representation of the influence of beaver dams to include short-term dynamism of flow states and potential triggers. Our study advances the understanding of the important, yet understudied, role of beaver dams in stream restoration and climate change initiatives.

Comparison of trace elements in tissue of beaver (Castor canadensis) and local vegetation from a rural region of southern Ontario, Canada.

Beavers have been analyzed in several studies examining trace elements (TEs) in wildlife; however, most of these studies were undertaken in areas with known environmental pollutants. To understand and quantify natural enrichments of TEs in beaver tissue, samples of kidney, liver, muscle from 28 animals were compared with bark from 40 species of trees and shrubs, from the same, uncontaminated watershed. Pearson correlation and factor analysis show that conservative, lithophile elements such as Al, Ga, Th, and Y, all surrogates for mineral dust particles, explain 61% of the variation in the bark data. In contrast, Cd, Co, Cu, Mn, Mo, Ni, Rb, Se, Sr, and Tl in bark are independent of Al, and therefore most likely occur in non-mineral forms. Comparing tissue concentrations of beaver and bark, the organs are enriched in micronutrients such as Cu, Fe, Mo, Se, and Zn, but also non-essential, benign elements such as Cs and Rb, and potentially toxic elements such as Cd and Tl. Thus, the elements most enriched in beaver organs are those that apparently occur in biological form in the plant tissue. The elements enriched in these animals, relative to bark, appear to offer the most promise for monitoring environmental contamination by TEs using beavers. The majority of TEs of environmental relevance are most abundant in beaver kidney. However, monitoring studies must consider the variation in TE concentrations in beaver tissue, including those due to sex and age. Also, due consideration must be given to background concentrations of TEs in the vegetation composing the diet of the animals. The natural enrichment in the case of elements such as Cd, in beaver tissue relative to bark, is profound. These data establish critical baseline values for TEs in beavers in an unpolluted environment, thereby allowing for their use as model organisms in tracking how heavy metal pollutants may affect wildlife.