The potential for restoring thermal refuges in rivers for cold-water salmonids
Human impacts to rivers have resulted in increased water temperatures that threaten cold water aquatic species such as salmonids (Schindler, 1998; Caissie, 2006; Justice et al., 2017). Higher summer water temperatures and lower winter water temperatures in rivers can lower fish viability by reducing fecundity, increasing morbidity and mortality, and reducing food sources (Konecki et al., 1995). This can result in localized species extirpation and overall reduction in habitat basin-wide (Batin et al., 2007; Ruesch et al., 2012). For cold-water aquatic species recovery programs to meet their long-term goals, they must consider mitigating the impacts of warming waters with "thermal restoration" and creation of thermal refuges.
Thermal refuge refers to areas within a stream corridor that buffer, lag, and cool/warm stream temperatures at biologically relevant scales and times (Arrigoni et al., 2008; Torgerson et al., 2012). Thermal refuge can be expressed as biologically-available areas within a stream where cooler water temperatures exist at base flow conditions during summer and warmer water temperatures during winter. Thermal refuge restoration refers to physical and biological stream habitat restoration practices that result in creating or enhancing thermal refuges. This may be accomplished by creating and enhancing connectivity between surface and groundwater systems in the hyporheic zone (the interface between surface and groundwater along a river bed and floodplain; Hester and Goosef 2010). Re-vegetating the riparian zone to promote shading can also promote thermal restoration. This study will focus on the former mechanism as it relates to thermal refuges for salmonids including: Chinook salmon, steelhead trout, and bull trout. XX
The Bureau of Reclamation (Reclamation) and other federal agencies have devoted significant resources into river habitat restoration for threatened and endangered aquatic organisms. Much of this restoration has focused on construct
Need and Benefit
This study will enable Reclamation to better and more cost-effectively restore thermal refuge for cold water aquatic species and better meet its environmental compliance objectives. It leverages existing monitoring data and partnerships to take a deeper dive into the physical and biological processes behind thermal restoration allowing us to gain and apply knowledge on future restoration work.
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