Extensive wetland drainage has occurred across the Canadian Prairies, and drainage activities are ongoing in many areas (Dahl 1990; Watmough and Schmoll 2007; Bartzen et al. 2010; Dahl 2014; Prairi...

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.

‘I would walk to the end of the street and out over the prairie with the clickety grasshoppers bunging in arcs ahead of me and I could hear the hum and twang of the wind in the great prairie harp o...

Hyporheic exchange is important in increasing stream water transit time through basins and enhancing redox-sensitive biogeochemical reactions influencing downstream water quality. Such exchange may be enhanced by beaver dams which are common throughout low order streams including those originating in peatlands. To understand the influence of beaver dams on hyporheic flows and biogeochemical properties, nitrogen (N), dissolved organic nitrogen (DOC) and N cycling rates were observed along a beaver dammed, third-order stream draining Canadian Rocky Mountain peatland. Beaver dams enlarged the hyporheric zone from ≤1.5 to ≥7.5 m. The looping hyporheic flow path created a zone of N and DOC depletion adjacent to the dams. As a result, nitrification rates were lowest in this zone. Where hyporheic flows exited the riparian area and flowed back to the stream channel downstream of a dam, the adjacent riparian area served as a source of N and DOC to the stream. Enhanced nutrient influx to streams owing to beaver dam modified hyporheic flow paths has implications for stream biogeochemical cycling and ecological integrity, which need further exploration.

Beaver dams are known to raise water tables in mineral soil environments but very little is known about their impact in wetlands, such as peatlands. Peatlands tend to have shallow water tables, and the position and tendency of the water table to fluctuate (i.e. stability) is a factor controlling the system's ability to store carbon and water. Many peatland environments, especially fens, offer ideal habitat for beaver and the potential for beaver dams to influence this link by manipulating water table dynamics requires investigation. Our objective was to determine the influence of beaver dams on water table dynamics of a Rocky Mountain fen. We monitored water tables in the peatland for four years while beaver dams were intact and two years after they were breached by an extreme flood event. We found that, because of the unique way in which dams were built, they connected the peatland to the stream and raised and stabilized already high water tables within a 150-m radius. Beaver-mediated changes to peatland water table regimes have the potential to enhance carbon sequestration and the peatland's ability to respond to external pressures such as climate change. Furthermore, beaver dams increased surface and groundwater storage, which has implications for regional water balances, especially in times of drought.