Water temperatures control life histories and diversity of aquatic species. Hydropower regulation, particularly in high head systems, alters natural water temperature regimes, which may have profound and long-term impacts on aquatic environments. Temperatures in by-pass sections and reaches affected by residual/environmental minimum flows fluctuate more than in natural flow regimes, driven more by influence of air temperatures. Reaches downstream of power plant outlets tend to become warmer in winter and colder in summer, driven by stratification behind the reservoir dam. In hydro-peaked systems high-low temperature effects may thus be aggravated. We review alterations of hydropower to natural thermal regimes, impacts on key organisms in terms of survival, development and behavioral thresholds, and potential mitigation measures, with focus on Atlantic salmon and brown trout in high northern latitude stream systems. Previous syntheses have focused mainly on flow changes and ecological impacts. Temperature effects may not always be correlated with flow changes, although there are some unique challenges with temperature changes in far northern latitudes, for example, related to the seasonal and colder climates. To help knowledge-based management and identify potential knowledge gaps, we review how hydropower regulation may impact seasonal water temperatures, what impacts changes to stream system temperature regimes may have to key organisms, for example, Atlantic salmon and brown trout, and what adaptations and behavioral variations they may exhibit to respond to changed temperature regimes, and finally what good practices can be recommended for mitigating temperature impacts. This synthesis indicates that there are impacts to the fish and their supporting food webs, in particular related to growth and development, and the potential for negative impacts seems higher, and better studied, than positive impacts in northern river systems. Some of these impacts may be modified by directed hydropower regulation practices, but here effect studies and knowledge are limited.

中文翻译：

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北部河流系统中水电驱动的热变化、生物响应和缓解措施

水温控制着水生物种的生命史和多样性。水电调节，特别是在高水头系统中，会改变自然水温状况，这可能对水生环境产生深远和长期的影响。受残余/环境最小流量影响的旁路部分和河段的温度比自然流态波动更大，更多地受空气温度的影响。受水库大坝后分层的影响，发电厂出口下游的河段往往冬暖夏凉。因此，在水力峰值系统中，高低温效应可能会加剧。我们审查了水电对自然热力状况的改变，对关键生物在生存、发展和行为阈值方面的影响，以及潜在的缓解措施，重点是北纬高纬度河流系统中的大西洋鲑鱼和褐鳟鱼。以前的综合主要集中在流量变化和生态影响上。温度影响可能并不总是与流量变化相关，尽管在远北纬度地区的温度变化存在一些独特的挑战，例如与季节性和较冷气候有关。为了帮助基于知识的管理和识别潜在的知识差距，我们回顾了水电监管如何影响季节性水温，河流系统温度制度的变化可能对关键生物（例如大西洋鲑鱼和褐鳟鱼）产生哪些影响，以及哪些适应和他们可能会表现出对温度变化的反应的行为变化，最后，可以推荐哪些良好做法来减轻温度影响。这种综合表明，鱼类及其支持的食物网受到影响，特别是与生长和发育相关的影响，与北部河流系统的积极影响相比，负面影响的可能性似乎更高，而且研究得更好。其中一些影响可能会被定向水电监管实践所改变，但这里的影响研究和知识是有限的。