Potential effects of climate change on streambed scour and risks to salmonid survival in snow‐dominated mountain basins

Abstract

Abstract:Snowmelt-dominated basins in northern latitudes provide critical habitat for salmonids. As such, these systems may be especially vulnerable to climate change because of potential shifts in the frequency, magnitude, and timing of flows that can scour incubating embryos. A general framework is presented to examine this issue, using a series of physical models that link climate change, streamflow, and channel morphology to predict the magnitude and spatial distribution of streambed scour and consequent risk to salmonid embryos at basin scales. The approach is demonstrated for a mountain catchment in the Northern Rocky Mountains, USA. Results show that risk of critical scour varies as a function of species and life history and is modulated by local variations in lithology and channel confinement. Embryos of smaller-bodied fall spawners may be at greater risk because of shallow egg burial depths and increased rain-on-snow events during their incubation period. Scour risk for all species is reduced when changes in channel morphology (width, depth, and grain size) keep pace with climate-driven changes in streamflow. Although climate change is predicted to increase scour magnitude, the frequency of scouring events relative to typical salmonid life cycles is relatively low, indicating that individual year classes may be impacted by critical scour, but extirpation of entire populations is not expected. Furthermore, refugia are predicted to occur in unconfined portions of the stream network, where scouring shear stresses are limited to bankfull stage because overbank flows spread across alluvial floodplains; conversely, confined valleys will likely exacerbate climate-driven changes in flow and scour. Our approach can be used to prioritize management strategies according to relative risk to different species or spatial distributions of risk and can be used to predict temporal shifts in the spatial distribution of suitable spawning habitats. A critical unknown issue is whether biological adaptation can keep pace with rates of climate change and channel response.

Modelling storage‐driven connectivity between landscapes and riverscapes: towards a simple framework for long‐term ecohydrological assessment

“…Goode et al, 2013). These modelling studies seek to understand in-stream ecological processes which are influ- enced by larger scale landscape hydrology, rather than simply in-stream hydraulics, such as the PHABSIM model (e.g.…”

“…Whilst there is a long-history of studies that look at the effects of flow regimes or local hydraulic interactions on in-stream biota in environmental flow assessment (e.g. see review in Gordon et al, 2004), relatively few of these have a wider hydrological landscape context as advocated by Tetzlaff et al (2007a). Recent work and the development of commercial software such as MIKE-SHE that allow such holistic studies have mainly used highly parameterized hydrological models (Loinaz et al, 2014).…”

“…Work to advance this agenda will involve a long-term analysis of annual and seasonal flow regimes in conjunction with fisheries data to examine how inter-and intra-annual flow regime variability explains variability in different components of the salmon population (Botter et al, 2013). In addition, the long-term flow modelling will be used to downscale inputs to hydraulic models for spatially distributed reaches of the river that are important habitats for key life stages where long-term observational data are available (cf Goode et al, 2013). The complex life cycle of Atlantic salmon renders such work extremely challenging as it needs to integrate conditions over 2 to 4 years of juvenile life spent in freshwaters with the 1-4 years spent at sea and associated density dependent controls on salmon populations (Gurney et al, 2008).…”

“…Loinaz et al, 2014). The output from these models is then used as input to other models such as hydraulic models to assess preference/avoidance of aquatic species (Goode et al, 2013) or process-based water quality models for simulating water temperature or other parameters (Loinaz et al, 2013). Of course, there is danger that there may be error propagation through such a modelling chain that renders the final output highly uncertain (Refsgaard et al, 2007).…”

Assessing freshwater life-stage vulnerability of an endangered Chinook salmon population to climate change influences on stream habitat

“…pdf). We also considered the potential for more frequent high flows during the in-gravel egg incubation and rearing stage, due to increases in precipitation (Warner et al 2014) and more transient hydrology dominated by both rain and snow (Mantua et al 2010), to increase streambed scour and so also egg and larval fish mortality (Lapointe et al 2000, Goode et al 2013. To simulate the population response to greater scour due to higher flows during the ingravel stage, we included a scenario with a 25% increase in mortality through this stage.…”