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.

Relative Effectiveness of Four Different Guards In Preventing Beaver Cutting of Urban Trees.

Beavers are expanding into cities as they recolonize their historic range. While they increase the ecological functioning of urban green areas, human-beaver conflicts occur. Public support to deal with conflicts has shifted from population to forage control. Tree guards are becoming popular with management personnel in North America and Europe to reduce damage to valuable trees. The problem is that this management technique has not been studied. We inventoried the tree guard types in use in natural and manicured river parks in the City of Saskatoon, Canada, determined their adherence to an installation protocol by measuring guard dimensions, and assessed the relative effectiveness of guards in protecting trees from beaver cutting. The inventory revealed that four types of tree guards are in use, ranging from light gauge chicken wire to heavy gauge chain link fencing. Overall, 11% of the trees with guards that we inventoried were cut by beavers, but variation among guard types was observed. Less than 10% of trees with type i and ii guards were beaver cut whereas 17% of trees with types iii and iv guards were beaver cut. Fewer trees were cut when there was adherence to installation protocol, regardless of guard type. Cut trees with guard types i, iii and iv experienced both minor and major damage whereas cut trees with guard type ii experienced only minor damage. The study results have implications for developing effectiveness and implementation monitoring plans for tree guards as part of an overall beaver management plan.

Beaver dams: How structure, flow state, and landscape setting regulate water storage and release.

Beaver (Castor canadensis and Castor fiber) are regarded widely as ecosystem engineers and the dams they create are well-known for their ability to drastically alter the hydrology of rivers. As a result, beaver are increasingly being included in green infrastructure practices to combat the effects of climate change and enhance ecosystem resilience. Both drought and flood mitigation capabilities have been observed in watersheds with beaver dam structures; however, how dams possess contrasting mitigation abilities is not fully understood since most studies neglect to acknowledge variation in beaver dam structures. In this study, an extensive cross-site survey of the physical and hydrologic properties of beaver dams was conducted in the Canadian Rocky Mountains in Alberta. This research aimed to improve the understanding of the hydrology of beaver dams by categorizing dams using their intrinsic properties and landscape settings to identify fundamental patterns that may be applicable across landscape types. The dam flow type classification from Woo and Waddington (1990) was evaluated in this new context and adapted to include two new flow types. The survey of intrinsic beaver dam properties revealed significant differences in dam structure across different sites. Physical differences in dam structure altered the dynamics and variance of pond storage and certain dam attributes related to the landscape setting. For instance, dam material influenced dam height and water source influenced dam length. However, a closer analysis of large rain events showed that the physical structure of dams alters seasonal dynamics of pond storage but not the response to rain events. Overall, this research shows that beaver dams can be both structurally and hydrologically very different from each other. Establishing broadly applicable classifications is vital to understanding the ecosystem resilience and mitigation services beaver dams provide.

Beaver dam capacity of Canada's boreal plain in response to environmental change.

Environmental changes are altering the water cycle of Canada's boreal plain. Beaver dams are well known for increasing water storage and slowing flow through stream networks. For these reasons beavers are increasingly being included in climate change adaptation strategies. But, little work focuses on how environmental changes will affect dam building capacity along stream networks. Here we estimate the capacity of the stream network in Riding Mountain National Park, Manitoba, Canada to support beaver dams under changing environmental conditions using a modelling approach. We show that at capacity, the park's stream network can support 24,690 beaver dams and hold between 8.2 and 12.8 million m3 of water in beaver ponds. Between 1991 and 2016 the park's vegetation composition shifted to less preferred beaver forage, which led to a 13% decrease in maximum dam capacity. We also found that dam capacity is sensitive to the size of regularly-occurring floods-doubling the 2-year flood reduces the park's dam capacity by 21%. The results show that the potential for beaver to offset some expected climatic-induced changes to the boreal water cycle is more complex than previously thought, as there is a feedback wherein dam capacity can be reduced by changing environmental conditions.

Flood Risk Management in Canada's Prairie Provinces: an Analysis of Decision-Maker Priorities and Policy Preferences.

If the aim of flood risk management (FRM) is to increase society's resilience to floods, then a holistic treatment of flood risk is required that addresses flood prevention, defence, mitigation, preparation, and response and recovery. Progressing resilience-based management to flood risk requires both diversity and coordination of policy across multiple jurisdictions. Decision makers and the types of FRM policy decisions they make play a key role in implementing FRM policies and strategies that progress flood resilience. This paper explores how policy preferences held by FRM decision makers relate to the characteristics of resilient FRM policy. The research was conducted in three flood-prone provinces in western Canada using a multi-criteria analytical approach. The results show that while decision maker FRM priorities are similar across the Canadian Prairies, their preferred FRM policies differ. Further, preferred FRM policies were largely resistance-based and influenced at least as much by flood experiences and perceptions of flood risk as by more obvious administrative pressures such as cost, public acceptability, and environmental protection. Several observations emerge from these results for advancing a coordinated, diversified approach to FRM which is required for resilience, both for western Canada and for FRM more broadly.

Alteration of hydrogeomorphic processes by invasive beavers in southern South America.

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 branches on streams, which triggered mineral sediment accretion processes in the riparian zone, but not in ways consistent with the beaver meadow theory and only at a few sites. At the majority of sites, beavers actively excavated peat and mineral sediment, moved thousands of cubic meters of sediment within their occupied landscapes and used it to build dams. Beaver were also common in fen ecosystems where pond formation inundated and drowned peat forming mosses and sedges, and triggered a massive invasion of exotic plant species. Results highlight that restoration of fen ecosystems is a previously unrecognized but pressing and challenging restoration need in addition to reforestation of Nothofagus riparian forests. We recommend that decision-makers include the full ecosystem diversity of the Fuegian landscape in their beaver eradiation and ecosystem restoration plans.

Beaver-mediated methane emission: The effects of population growth in Eurasia and the Americas.

Globally, greenhouse gas budgets are dominated by natural sources, and aquatic ecosystems are a prominent source of methane (CH(4)) to the atmosphere. Beaver (Castor canadensis and Castor fiber) populations have experienced human-driven change, and CH(4) emissions associated with their habitat remain uncertain. This study reports the effect of near extinction and recovery of beavers globally on aquatic CH4 emissions and habitat. Resurgence of native beaver populations and their introduction in other regions accounts for emission of 0.18-0.80 Tg CH(4) year(-1) (year 2000). This flux is approximately 200 times larger than emissions from the same systems (ponds and flowing waters that became ponds) circa 1900. Beaver population recovery was estimated to have led to the creation of 9500-42 000 km(2) of ponded water, and increased riparian interface length of >200 000 km. Continued range expansion and population growth in South America and Europe could further increase CH(4) emissions.

Assessing large spatial scale landscape change effects on water quality and quantity response in the lower Athabasca River basin.

Increased land use intensity has been shown to adversely affect aquatic ecosystems. Multiple landscape stressors interact over space and time, producing cumulative effects. Cumulative Effects Assessment (CEA) is the process of evaluating the impact a development project may have on the ecological surroundings, but several challenges exist that make current approaches to cumulative effects assessment ineffective. The main objective of this study was to compare results of different methods used to link landscape stressors with stream responses in a highly developed watershed, where past work has shown that the river has experienced significant water quality and quantity changes to improve approaches to CEA. The study site was the lower reaches of the Athabasca River, Canada that have been subjected to a diverse range of intense anthropogenic developments since the late 1960s. Linkages between landscape change and river response were evaluated using correlation analyses, stepwise, multiple regression, and regression trees. Notable landscape changes include increased industrial development and forest cut-blocks, made evident from satellite imagery and supporting ancillary data sets. Simple regression analyses showed water use was closely associated with total phosphorus (TP) and Na(+) concentrations, as well as specific conductance. The regression trees for total organic carbon (TOC), TP, and Na(+) showed that the landscape variables that appear as the first characteristic were the same variables that showed significant relations for their respective simple regression models. Simple, stepwise, and multiple regressions in conjunction with regression trees were useful in this study for capturing the strongest associations between landscape stressors and river response variables. The results highlight the need for improved scaling methods and monitoring strategies crucial to managing cumulative effects to river systems.

An approach for assessing cumulative effects in a model river, the Athabasca River basin.

Novel approaches addressing aquatic cumulative effects over broad temporal and spatial scales are required to track changes and assist with sustainable watershed management. Cumulative effects assessment (CEA) requires the assessment of changes due to multiple stressors both spatially and temporally. The province of Alberta, Canada, is currently experiencing significant economic growth as well as increasing awareness of water dependencies. There has been an increasing level of industrial, urban, and other land-use related development (pulp and paper mills, oil sands developments, agriculture, and urban development) within the Athabasca River basin. Much of the historical water quantity and quality data for this basin have not been integrated or analyzed from headwaters to mouth, which affects development of a holistic, watershed-scale CEA. The main objectives of this study were 1) to quantify spatial and temporal changes in water quantity and quality over the entire Athabasca River mainstem across historical (1966­1976) and current day (1996­2006) time periods and 2) to evaluate the significance of any changes relative to existing benchmarks (e.g., water quality guidelines). Data were collected from several federal, provincial, and nongovernment sources. A 14% to 30% decrease in discharge was observed during the low flow period in the second time period in the lower 3 river reaches with the greatest decrease occurring at the mouth of the river. Dissolved Na, sulfate, chloride, and total P concentrations in the second time period were greater than, and in some cases double, the 90th percentiles calculated from the first time period in the lower part of the river. Our results show that significant changes have occurred in both water quantity and quality between the historical and current day Athabasca River basin. It is known that, in addition to climatic changes, rivers which undergo increased agricultural, urban, and industrial development can experience significant changes in water quantity and quality due to increased water use, discharge of effluents, and surface run-off. Using the results from this study, we can begin to quantify dominant natural and man-made stressors affecting the Athabasca River basin as well as place the magnitude of any local changes into an appropriate context relative to trends in temporal and spatial variability.