Many anthropogenic disturbances impact stream ecosystems by changing flow and temperature regimes. The emerging industry of small Run‐of‐River (RoR) hydropower reduces streamflow in bypassed reaches, with largely unknown consequences for water temperatures and fish growth. We used empirical and simulated data from two small RoR regulated streams in British Columbia (Canada) to quantify changes in water temperatures in bypassed reaches and assess the potential impacts to resident rainbow trout (Oncorhynchus mykiss) growth using bioenergetics models under a range of consumption scenarios. We found increases in mean monthly water temperature in bypassed reaches due to flow diversion of 0.5–0.8°C (0.17–0.19°C/km). Bioenergetics models using those temperatures predicted increases in annual O. mykiss growth (compared to natural temperatures) if consumption was unlimited (+200–450%), increases (+15–42%) if consumption was scaled with higher metabolic demand, and small reductions (−5 to 7%) if consumption remained constant. If food availability was reduced by 25%, annual growth was predicted to decline by 45%. Empirical estimates of annual growth of fish sampled indicate modest reductions in annual growth less severe than those modelled by our Scenario 2. Our results highlight that increases in water temperature induced by flow diversion for small RoR hydropower could be large enough to have consequences for O. mykiss growth, but the impacts depend on how and when RoR hydropower affects food supply and consumption.

中文翻译：

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河道水力发电分流对鲑鱼旁路流温度和生物能的预测影响

许多人为干扰会通过改变流量和温度范围来影响河流生态系统。小型河道（RoR）水力发电的新兴产业减少了绕过河段的水流，对水温和鱼类生长的后果尚不明了。我们使用来自不列颠哥伦比亚省（加拿大）的两个小的RoR调节流的经验和模拟数据来量化绕过河段中水温的变化，并在一系列消费情景下使用生物能模型评估对虹鳟（Oncorhynchus mykiss）增长的潜在影响。我们发现，由于分流0.5-0.8°C（0.17-0.19°C / km），旁路河段的平均每月水温增加。使用这些温度的生物能学模型预测了每年的O. mykiss会增加如果消费不受限制（+ 200–450％），则增长（与自然温度相比）；如果按新陈代谢的需求增加消费，则增加（+ 15–42％）；如果消费保持不变，则小幅减少（-5至7％） 。如果将粮食供应量减少25％，则预计年增长率将下降45％。对鱼的年生长进行的经验估计表明，年增长率的适度下降幅度不如我们的情景2所模拟的那么严重。我们的结果表明，小型RoR水力发电通过分流引起的水温升高可能大到足以给O带来后果。 mykiss增长，但影响取决于RoR水电如何以及何时影响粮食供应和消费。