Summer temperature regimes in southcentral Alaska streams: watershed drivers of variation and potential implications for Pacific salmon

Abstract

Abstract:Climate is changing fastest in high-latitude regions, focusing our research on understanding rates and drivers of changing temperature regimes in southcentral Alaska streams and implications for salmon populations. We collected continuous water and air temperature data during open-water periods from 2008 to 2012 in 48 nonglacial salmon streams across the Cook Inlet basin spanning a range of watershed characteristics. The most important predictors of maximum temperatures, expressed as mean July temperature, maximum weekly average temperature, and maximum weekly maximum temperature (MWMT), were mean elevation and wetland cover, while thermal sensitivity (slope of the stream-air temperature relationship) was best explained by mean elevation and area. Although maximum stream temperatures varied widely between years and across sites (8.4 to 23.7°C), MWMT at most sites exceeded established criterion for spawning and incubation (13°C), above which chronic and sublethal effects become likely, every year of the study, which suggests salmon are already experiencing thermal stress. Projections of MWMT over the next ϳ50 years suggest these criteria will be exceeded at more sites and by increasing margins.Résumé : Les changements climatiques sont les plus rapides dans les régions de haute latitude, et nos travaux tentent de comprendre les taux et facteurs associés à l'évolution des régimes thermiques dans les cours d'eau du centre-sud de l'Alaska et leurs répercussions sur les populations de saumons. Nous avons recueilli de manière continue des données de température de l'eau et de l'air durant des périodes d'eau libre de 2008 à 2012 dans 48 cours d'eau non glaciaires à saumons à la grandeur du bassin versant du golfe de Cook représentant un éventail de caractéristiques hydrographiques. Les plus importantes variables prédictives des températures maximums, exprimées comme étant la température moyenne en juillet, la température moyenne hebdomadaire maximum et la température maximum hebdomadaire maximum (TMHM), étaient l'altitude moyenne et la couverture de milieux humides, alors que l'altitude moyenne et la superficie étaient les variables qui expliquaient le mieux la sensibilité thermique (la pente de la relation entre la température du cours d'eau et celle de l'air). Si les températures maximums du cours d'eau variaient beaucoup (de 8,4 à 23,7°C) d'une année et d'un emplacement à l'autre, la TMHM dans la plupart des emplacements dépassait le seuil établi pour le frai et l'incubation (13°C) au-delà duquel des effets chroniques et sublétaux deviennent probables, chaque année de l'étude, donnant à penser que les saumons sont déjà en situation de stress thermique. Les projections de la TMHM pour les ϳ50 prochaines années portent à croire que ces seuils seront dépassés dans un nombre croissant d'emplacements et par une plus grande marge. [Traduit par la Rédaction]

Empirical Stream Thermal Sensitivities May Underestimate Stream Temperature Response to Climate Warming

“…Empirical stream thermal sensitivity has been widely used to characterize historic stream temperature conditions and also to predict how streams might respond to future climate warming (Isaak et al, , ; Mauger et al, ). These types of methods, which rely on regressions between stream and air temperatures, have been criticized for not adequately representing the underlying processes controlling stream temperature (Arismendi et al, ; Johnson, ).…”

“…Luce et al (2014) argued that using interannual mean temperatures, such as mean August or mean summer temperatures, is preferable over subannual temperatures since models fit to subannual temperatures will be confounded by annual hysteresis in the relation between stream temperature and solar radiation. However, a drawback of using interannual temperatures is that few long-term records exist, and although with increased and continuing monitoring efforts, this situation is changing (Isaak et al, 2017;Luce et al, 2014).Empirical stream thermal sensitivity has been widely used to characterize historic stream temperature conditions and also to predict how streams might respond to future climate warming (Isaak et al, 2016(Isaak et al, , 2018Mauger et al, 2017). These types of methods, which rely on regressions between stream and air temper-…”

“…Empirical stream thermal sensitivity has been widely used to characterize historic stream temperature conditions and also to predict how streams might respond to future climate warming (Isaak et al, 2016(Isaak et al, , 2018Mauger et al, 2017). These types of methods, which rely on regressions between stream and air temper-…”

Can spatial statistical river temperature models be transferred between catchments?

“…For example, Fellman et al (2014) observed slopes of between −0.180 and 1.282 across nine watersheds in Alaska depending on glacial influence, while Mauger et al (2017) observed slopes of between 0.32 and 1.51 across 48 non-glacial streams in Alaska which related to mean elevation and catchment area. Similarly, Tague et al (2007) observed systematic regional differences in T w -T a relationships in western Oregon that depended on local hydrogeology and concluded that under such circumstances air temperature alone (i.e.…”

“…Many studies have shown that within-year temporal relationships between T w and T a (often termed thermal or climate sensitivity) can be highly variable between sites and catchments, and importantly this variability relates to regional, hydrological and landscape controls (Tague et al, 2007;Kelleher et al, 2012;Krider et al, 2013;Chang and Psaris, 2013;Hilderbrand et al, 2014;Segura et al, 2015;Mauger et al, 2017). For example, Fellman et al (2014) observed slopes of between −0.180 and 1.282 across nine watersheds in Alaska depending on glacial influence, while Mauger et al (2017) observed slopes of between 0.32 and 1.51 across 48 non-glacial streams in Alaska which related to mean elevation and catchment area.…”