Stream Physical Characteristics Impact Habitat Quality for Pacific Salmon in Two Temperate Coastal Watersheds

Abstract

Climate warming is likely to cause both indirect and direct impacts on the biophysical properties of stream ecosystems especially in regions that support societally important fish species such as Pacific salmon. We studied the seasonal variability and interaction between stream temperature and DO in a low-gradient, forested stream and a glacial-fed stream in coastal southeast Alaska to assess how these key physical parameters impact freshwater habitat quality for salmon. We also use multiple regression analysis to evaluate how discharge and air temperature influence the seasonal patterns in stream temperature and DO. Mean daily stream temperature ranged from 1.1 to 16.4°C in non-glacial Peterson Creek but only 1.0 to 8.8°C in glacial-fed Cowee Creek, reflecting the strong moderating influence glacier meltwater had on stream temperature. Peterson Creek had mean daily DO concentrations ranging from 3.8 to 14.1 mg L−1 suggesting future climate changes could result in an even greater depletion in DO. Mean daily stream temperature strongly controlled mean daily DO in both Peterson (R2=0.82, P<0.01) and Cowee Creek (R2=0.93, P<0.01). However, DO in Peterson Creek was mildly related to stream temperature (R2=0.15, P<0.01) and strongly influenced by discharge (R2=0.46, P<0.01) on days when stream temperature exceeded 10°C. Moreover, Peterson Creek had DO values that were particularly low (<5.0 mg L−1) on days when discharge was low but also when spawning salmon were abundant. Our results demonstrate the complexity of stream temperature and DO regimes in coastal temperate watersheds and highlight the need for watershed managers to move towards multi-factor risk assessment of potential habitat quality for salmon rather than single factor assessments alone.

Developing flow–ecology relationships: Implications of nonlinear biological responses for water management

“…Solid line represents the mean response, broken lines are 95% confidence intervals (lower limb regression: DO = 0.74 · % MAD + 1.99; upper limb regression: DO = 0.08 · % MAD + 5.46; R 2 = .56, F 3,177 = 74.4, p < .0001. (c) Effects of flow and the presence of salmon carcases on mean daily dissolved oxygen in non‐eutrophic Peterson Creek, Alaska (Fellman et al., , see Supporting Information); dissolved oxygen at saturation is represented by the solid line ( DO = −0.47 · Temp (°C) + 15; R 2 = .90, F 1,66 = 589, p < .0001). Reduction in dissolved oxygen in the presence of salmon carcases (relative to saturation) is exacerbated at low discharge [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…However, temperature and dissolved oxygen can be decoupled at higher temperatures, when low flow becomes a more important driver of reduced dissolved oxygen (e.g. Fellman, Hood, Dryer, & Pyare, ; Graeber et al., ). Elevated temperature and low dissolved oxygen have synergistic negative impacts on cold‐water taxa like trout, causing oxygen limitation at the same time that warming triggers an exponential increase in metabolism (Breau, Cunjak, & Peake, ; Pörtner, ; Pörtner & Knust, ).…”

High salmon density and low discharge create periodic hypoxia in coastal rivers

“…Our model may not perform as well in small‐ to medium‐sized watersheds in the NPCTR with high percentages of wetland coverage (>30%) and more complicated groundwater dynamics or lake systems contributing significant flow to downstream channels (e.g., see Peterson Creek in Fellman et al. ).…”

“…, Fellman et al. ). Salmon nest building, for instance, has been shown to increase air–water gas exchange (Holtgrieve and Schindler ) and reduce the abundance of benthic organisms (Moore and Schindler , Collins et al.…”

“…In small watersheds (<30 km 2 ), dense spawning salmon can significantly modify the physical and chemical characteristics of rivers through processes such as respiration, nest building, and carcass decomposition (Montgomery et al 1996, Peterson and Foote 2000, Moore et al 2004, Holtgrieve and Schindler 2011, Levi et al 2013, Fellman et al 2015. Salmon nest building, for instance, has been shown to increase air-water gas exchange (Holtgrieve and Schindler 2011) and reduce the abundance of benthic organisms (Moore and Schindler 2008, Collins et al 2011, Campbell et al 2012.…”