Effects of land use on summer thermal regimes in critical salmonid habitats of the Pacific Northwest

Abstract

The effect of climate change on stream temperature regimes is of significant concern to natural resource managers focused on protecting cold-water-dependent species. Nevertheless, understanding of how human land-use activities may act to exacerbate the effects of climate change on stream temperature regimes is limited. Using extensive stream temperature data with high-resolution climate and habitat data, we quantified how land management activities are related to summer stream temperatures across the Pacific Northwest, USA. We then described the distribution of land management practices influencing summer thermal regimes relative to the distribution of salmonid fish species of conservation concern. After accounting for climatic and geophysical variation, we detected a strong relationship between livestock grazing and summer thermal regimes. Maximum, average, and diel variation in water temperature was greater where livestock grazing was present. Livestock grazing was widespread, occurring in 43%–100% of sites supporting salmonid species of conservation concern. Thus, current land management practices may be intensifying the effects of ongoing climate change in freshwater habitats, acting to further threaten cold-water fishes of conservation concern.

Principal components of thermal regimes in mountain river networks

“…Not surprisingly given the pronounced elevational gradients in the study landscape, the dominant regime aspect represented by PC1 in the metric-based PCA was associated with magnitude. Less expected was that many of the variability metrics also loaded heavily on the first PC because variation has been treated as a distinct element of thermal regimes (e.g., Steel et al, 2012;Kovach et al, 2018). The concurrence of magnitude and variability metrics probably also relates to elevation and changes in the importance of groundwater buffering, which both cools streams and dampens diurnal and seasonal variations (Caissie and Luce, 2017).…”

“…Temperatures of flowing waters control many physicochemical processes (Likens and Likens, 1977;Gordon et al, 1991;Ducharne, 2008) and affect the ecology of aquatic organisms and communities (Isaak et al, 2017b;Neuheimer and Taggart, 2007;Woodward et al, 2010). Knowledge of thermal regimes, characterized as the annual sequence of temperature conditions specific to locations within river networks (Caissie, 2006), is key to understanding natural conditions and diagnosing anthropogenic impairments.…”

Phylogenetic diversity efficiently and accurately prioritizes conservation of aquatic macroinvertebrate communities

“…Some managers may be able to address factors that we designate as non‐actionable. For example, grazing is known to impact instream temperatures (Belsky et al 1999, Hough‐Snee et al 2013, Kovach et al 2019), and thus, altering grazing intensity could be used to alter temperature and thus help remediate the site. By accounting for what cannot be changed and acting on what can, managers will effectively and efficiently be able to apply these metrics.…”

Effects of climate change on the life stages of stream‐dwelling brown trout (Salmo trutta Linnaeus, 1758) at the rear edge of their native distribution range

“…In the case at hand, and among the main and potentially effective management measures, increasing shading could be an applicable one; however, our rivers are intensely shaded and it only would be applicable in specific sites leading to a limited impact. Besides, the effect of land use on the local and regional climate is known (Kovach, Muhlfeld, Al‐Chokhachy, Ojala, & Archer, 2019; Stohlgren, Chase, Pielke, Kittel, & Baron, 1998). Thus, in the middle and lower reaches of the Cega River, action could be taken to manage the land use of the basin to moderate the local temperature and increase the water retention of the soil.…”