Papers by Cherie Westbrook
Authorea (Authorea), Jul 8, 2023
Beavers modify stream channels and their floodplains by building dams that alter downstream fluxe... more Beavers modify stream channels and their floodplains by building dams that alter downstream fluxes of water and sediment. Where beavers have been lost and stream channels degraded, beaver dam analogues (BDAs) are being used to mimic the effects of beaver engineering. Central to the success of these structures in accelerating stream recovery is creating similar channel responses as beaver dams. Unknown is the importance of beaver actions versus erosion in the catchment in generating the retained sediment. This study tested the viability of sediment fingerprinting to determine the source of sediment retained by beaver dams and BDAs at a watershed in Alberta, Canada. Elemental concentrations were determined in potential sediment sources (forest, grassland, floodplain, stream bank, and beaver canal) and sediment collected from the upstream face of beaver dams and BDAs. Of the 29 elements evaluated, only Se and Ti could discriminate potential sediment sources in this watershed. Mixing models showed that about 55% of the sediment retained by the beaver dams originated from floodplains, 23% from upland sources, and 13% from beaver canals whereas about 89% of sediment retained by the BDAs originated from eroding stream banks. Our findings indicate that sediment fingerprinting is a viable technique for identifying sources of sediment retained by beaver ponds and BDAs. The actions of beavers, a known geomorphic agent, are important in actively eroding the sediment that becomes retained by their dams. The study has implications for determining the processes by which BDAs cause channel aggradation.
<p>Beavers profoundly alter streams by building dams. Beaver dams change how water, sedimen... more <p>Beavers profoundly alter streams by building dams. Beaver dams change how water, sediment, nutrients and energy flow through stream corridors enhancing both habitat diversity and landscape connectivity. Humans are captivated by learning from nature and trying to mimic it, especially in human-degraded environments. There is considerable eagerness for using beaver dam analogues (BDAs), also called simulated beaver structures, as low-tech, low cost solutions for restoring the functioning of degraded streams where beavers are not present and cannot survive. The use of BDAs in stream enhancement projects, especially in the western United States, is outpacing the research, leading to questions about whether BDAs do, in fact, yield similar ecosystem-scale effects as natural beaver dams. We review the different names used for BDAs, discuss the many ways these structures can be built and how different types function, and how they compare to real beaver dams. We conclude the talk by exploring what we can expect from various types of BDAs in the short and long term and whether these structures can lead to stream and riparian zone restoration that can facilitate the return of beavers.&#160;</p>
River Research and Applications, 2020
Beaver dam analogues (BDAs) are intended to simulate natural beaver dam ecohydrological functions... more Beaver dam analogues (BDAs) are intended to simulate natural beaver dam ecohydrological functions including modifying stream hydrology and enhancing stream‐riparian hydrological connectivity. River restoration practitioners are proactively deploying BDAs in thousands of degraded streams. How various BDAs or their configurations impact stream hydrology and the riparian water table remains poorly understood. We investigated three types of BDA configurations (single, double and triple) in a spring‐fed Canadian Rocky Mountain stream over three study seasons (April–October; 2017–2019). All three BDA configurations significantly elevated the upstream stage. The deepest pools occurred upstream of the triple‐configuration BDAs (0.46 m) and the shallowest pools occurred upstream of the single‐configuration (0.36 m). Further, the single‐BDA configuration lowered stream stage and flow peaks below it but raised low flows. The double‐BDA configuration modulated flow peaks but had little influenc...
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Populations of beaver and willow have not thrived in riparian environments that are heavily 1 bro... more Populations of beaver and willow have not thrived in riparian environments that are heavily 1 browsed by livestock or ungulates, such as elk. The interaction of beaver and elk herbivory may be an 2 important mechanism underlying beaver and willow declines in this competitive environment. We 3 conducted a field experiment that compared the standing crop of willow 3 years after simulated 4 beaver cutting on paired plants with and without intense elk browsing (~85% utilization rate). 5 Simulated beaver cutting with intense elk browsing produced willow that was small (biomass and 6 diameter) and short with far fewer but longer shoots and a high percentage of dead biomass. In 7 contrast, simulated beaver cutting without elk browsing produced willow that was large, tall, and 8 leafy with many more but shorter shoots (highly branched) and a low percentage of dead biomass. 9
Mountain lakes are distinctive water bodies that not only serve as a crucial water resource for t... more Mountain lakes are distinctive water bodies that not only serve as a crucial water resource for the inhabitants of the upland regions but also as an important destination for millions of tourists who are attracted by their beauty. Mountain lakes are fragile water bodies that are experiencing changes in their hydrological processes owing to global warming. Understanding the consequences is important as it can help identify whether climate change causes degradations in lake hydrological functioning. The interactions of hydrological processes in mountain lakes with external drivers are usually hard to explain explicitly owing to their complexity. To deal with that problem, scholars develop conceptual frameworks. The focus was on the Canadian Rocky Mountains where 5155 lakes were identified using GIS. To identify factors influencing lake hydrological function and their sensitivity to changing climate, a literature review was undertaken. Identified in the literature review were 13 natura...
Land Use Policy, 2021
Abstract Ecosystem services valuation is not new, but few approaches have been developed to suppo... more Abstract Ecosystem services valuation is not new, but few approaches have been developed to support ecosystem service consideration at the strategic level of futures-based planning. This paper demonstrates a practical, strategic environmental assessment approach to incorporate the valuation of ecosystem services in a futures-based assessment to support land use planning decisions for urban ecological areas. The application is based on the Northeast Swale, a valued natural area consisting of prairie grasslands and ephemeral wetlands in Saskatoon, Saskatchewan, Canada, which is subject to the cumulative pressures of urban development. Land use attributes or end points are adopted as proxies for ecosystem services to simplify the complexity of ecosystem services and to ensure outcomes that are practical and relevant to those who make land use decisions. The value of land use attributes is assessed using a choice experiment that incorporates visual interpretations of alternative land use futures, from which residents’ marginal willingness to pay for attributes are determined. Using compensating surplus values, tradeoffs between alternative future scenarios are explored and a range of preferred land use futures identified that depict different land use attributes and thus the suite of benefits residents derive from ecosystem services. Lessons are discussed for improved integration of ecosystem services valuation in strategic land use planning, and for translating complex ecosystem service concepts into practical directions for urban residents and for those responsible for land use policy and planning decisions.
Journal of Urban Ecology, 2021
Beavers have recolonized much of their historic range throughout the northern hemisphere and nume... more Beavers have recolonized much of their historic range throughout the northern hemisphere and numerous studies have documented their habitat preferences and foraging behavior in rural riparian areas. Beavers, however, are also recolonizing waterways in cities, yet there has been little study of habitat use and foraging practices in these managed, urban systems. We studied beaver lodge distribution and riparian foraging preferences along the South Saskatchewan River, Canada, comparing a reach (24 km) passing through the City of Saskatoon where beavers and trees are managed with an upstream reach (29 km) passing through a conservation area where neither beavers nor trees are managed. In a canoe-based census at low flow, we found that beaver density in the conservation area was twice that in the city. Lodges were dispersed in the city with longer water-based distances between them. We found both differences and similarities in beaver foraging behavior. Riparian tree sampling along trans...
Hydrological Processes, 2020
It is becoming increasingly popular to reintroduce beaver to streams with the hopes of restoring ... more It is becoming increasingly popular to reintroduce beaver to streams with the hopes of restoring riparian ecosystem function or reducing some of the hydrological impacts of climate change. One of the risks of relying on beaver to enhance ecosystem water storage is that their dams are reportedly more apt to fail during floods which can exacerbate flood severity. Missing are observations of beaver dam persistence and water storage capacity during floods, information needed to evaluate the risk of relying on beaver as a nature‐based flood solution. A June rainstorm in 2013 triggered the largest recorded flood in the Canadian Rocky Mountains west of Calgary, Alberta. We opportunistically recorded hydrometric data during the rainfall event at a beaver‐occupied peatland that has been studied for more than a decade. We supplemented these observations with a post‐event regional analysis of beaver dam persistence. Results do not support two long‐held hypotheses—that beaver ponds have limited flood attenuation capacity and commonly fail during large flood events. Instead we found that 68% of the beaver dam cascade systems across the region were intact or partially intact after the event. Pond fullness, in addition to the magnitude of the water‐sediment surge, emerged as important factors in determining the structural fate of dam cascade sequences. Beaver ponds at the instrumented site quickly filled in the first few hours of the rain event and levels were dynamic during the event. Water storage offered by the beaver ponds, even ones that failed, delayed downstream floodwater transmission. Study findings have important implications for reintroducing beaver as part of nature‐based restoration and climate change adaptation strategies.
River Research and Applications, 2019
River management based solely on physical science has proven to be unsustainable and unsuccessful... more River management based solely on physical science has proven to be unsustainable and unsuccessful, evidenced by the fact that the problems this approach intended to solve (e.g., flood hazards, water scarcity, and channel instability) have not been solved and long-term deterioration in river environments has reduced the capacity of rivers to continue meeting the needs of society. In response, there has been a paradigm shift in management over the past few decades, towards river restoration. But the ecological, morphological, and societal benefits of river restoration have, on the whole, been disappointing. We believe that this stems from the fact that restoration overrelies on the same physical analyses and approaches, with flowing water still regarded as the universally predominant driver of channel form and structural intervention seen as essential to influencing fluvial processes. We argue that if river restoration is to reverse long-standing declines in river functions, it is necessary to recognize the influence of biology on river forms and processes and re-envisage what it means to restore a river. This entails shifting the focus of river restoration from designing and constructing stable channels that mimic natural forms to reconnecting streams within balanced and healthy biomes, and so levering the power of biology to influence river processes. We define this new approach as biomic river restoration.
Hydrological Processes, 2017
Modeling nutrient transport during snowmelt in cold regions remains a major scientific challenge.... more Modeling nutrient transport during snowmelt in cold regions remains a major scientific challenge. A key limitation of existing nutrient models for application in cold regions is the inadequate representation of snowmelt, including hydrological and biogeochemical processes. This brief period can account for more than 80% of the total annual surface runoff in the Canadian Prairies and Northern Canada and processes such as atmospheric deposition, over-winter redistribution of snow, ion exclusion from snow crystals, frozen soils, and snowcovered area depletion during melt influence the distribution and release of snow and soil nutrients, thus affecting the timing and magnitude of snowmelt runoff nutrient concentrations. Research in cold regions suggests that nitrate (NO3) runoff at the field scale can be divided into five phases during snowmelt. In the first phase, water and ions originating from ion-rich snow layers travel and diffuse through the snowpack. This process causes ion concentrations in runoff to gradually increase. The second phase occurs when this snow ion meltwater front has reached the bottom of the snowpack and forms runoff to the edge-of-the-field (EOF). During the third and fourth phases, the main source of NO3 transitions from the snowpack to the soil. Finally, the fifth and last phase occurs when the snow has completely melted, and the thawing soil becomes the main source of NO3 to the stream. In this research, a process-based model was developed to simulate hourly export based on this five-phase approach. Results from an application in the Red River Basin of southern Manitoba, Canada shows that the model can adequately capture the dynamics and rapid changes of NO3 concentrations during this period at relevant temporal resolutions. This is a significant achievement to advance the current nutrient modeling paradigm in cold climates, which is generally limited to satisfactory results at monthly or annual resolutions. The approach can inform catchment-scale nutrient models to improve simulation of this critical snowmelt period. Nutrient exports Winter Snow Nitrate Agriculture Nutrient model
Hydrology and Earth System Sciences Discussions, 2016
Beaver ponds are surface water features that are transient through space and time. Such qualities... more Beaver ponds are surface water features that are transient through space and time. Such qualities complicate the inclusion of beaver ponds in local and regional water balances, and in hydrological models, as reliable estimates of surface water storage are difficult to acquire without time and labour intensive topographic surveys. A simpler approach to overcome this challenge is needed, given the abundance of the beaver ponds in North America, Eurasia and southern South America. We investigated whether simple morphometric characteristics derived from readily available aerial imagery or quickly measured field attributes of beaver ponds can be used to approximate surface water storage among the range of environmental settings in which beaver ponds are found. Studied were a total of 40 beaver ponds from four different sites in North and South America. The Simplified V-A-h approach, originally developed for prairie potholes, was tested. With only two measurements of pond depth and corresponding surface area, this method estimated surface water storage in beaver ponds within 5% on average. Beaver pond morphometry was characterized by a median basin coefficient of 0.91, and dam length and pond surface area were strongly correlated with beaver pond storage capacity, regardless of geographic setting. These attributes provide a means for coarsely estimating surface water storage capacity in beaver ponds. Overall, this research demonstrates that reliable estimates of surface water storage in beaver ponds only requires simple measurements derived from aerial imagery and/or brief visits to the field. Future research efforts should be directed at incorporating these simple methods into both broader beaverrelated tools and catchment scale hydrological models.
The Science of the total environment, Jan 13, 2016
The North American beaver (Castor canadensis) is an invasive species in southern Patagonia, intro... more The North American beaver (Castor canadensis) is an invasive species in southern Patagonia, introduced in 1946 as part of a program by the Argentine government to augment furbearers. Research focus has turned from inventorying the beaver's population and ecosystem impacts toward eradicating it from the region and restoring degraded areas. Successful restoration, however, requires a fuller determination of how beavers have altered physical landscape characteristics, and of what landscape features and biota need to be restored. Our goal was to identify changes to the physical landscape by invasive beaver. We analyzed channel and valley morphology in detail at one site in each of the three major forest zones occurring on the Argentine side of Tierra del Fuego's main island. We also assessed 48 additional sites across the three forest biomes on the island to identify a broader range of aquatic habitat occupied and modified by beaver. Beaver build dams with Nothofagus tree branch...
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Papers by Cherie Westbrook