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.
Highlights
Alaska is a globally important wild-salmon producing region [1], with more than 4,000 natural runs in southeast Alaska alone [2]
Streamwater δ18O values averaged -13.0‰ for Peterson Creek and -14.5‰ for Cowee Creek across the study period reflecting differences in the relative contributions of glacial meltwater and precipitation to streamflow (Fig 2B; Table 1)
Cowee Creek had δ18O values below -15.0‰ through most of August reflecting the contribution of glacier meltwater to streamflow, with values only becoming more similar to the seasonal mean δ18O signature of rainfall in October
Summary
Alaska is a globally important wild-salmon producing region [1], with more than 4,000 natural runs in southeast Alaska alone [2]. Characterizing suitable aquatic habitat for salmon in coastal watersheds is becoming an increasingly important component of watershed management in light of rapid environmental change in the region. Of particular importance is the potential these environmental changes have for altering thermal regimes in coastal salmon-producing streams in Alaska [6,7,8,9]. In addition to temperature, dissolved oxygen (DO) is an important control on inland aquatic habitat for salmonids because DO levels exert a strong influence on salmonid behavior and metabolic activity [13,15]. Low concentrations of DO can be lethal to salmon, sub-lethal effects are far more common and include impacts to the growth and development of salmon at different life stages, decreased feeding activity, reduced swimming performance and prevention of upstream migration [15,16,17]
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