Hydropower‐driven thermal changes, biological responses and mitigating measures in northern river systems

Abstract

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.

Temperature regime during embryogenesis alters subsequent behavioural phenotypes of juvenile brown trout

“…All this considered, if the extension of the growth period allows hatchlings to grow large enough to overwinter regardless of activity and explorative levels, the reduction in activity and exploration levels in response to warmer temperatures during embryogenesis could be favoured since the predation risk would be reduced. At the same time, however, warmer temperatures during embryogenesis, which occurs in winter, may also affect the densities and traits of predators and prey of the hatchlings [ 44 ]. This will further complicate the effects of the reduced activity and exploration levels on early growth and survival.…”

Water Scarcity – A Concealed Phenomenon in Sri Lanka: A Mini Review

“…Unawareness of the irrigation water users on permitted water quantity, flood irrigation, improper contour leveling, and deep percolation due to low land−soil management in the field also increases the water losses at the field level (Sirimewan, 2019). 69 However, releasing temperature-altered water from high-head system hydropower plants (Heggenes et al, 2021) 70 could influence downstream water scarcity, but it has yet to be discovered.…”

Fisheries Volume 48 Number 8 August 2023

“…A warming climate is of great concern for fi sheries professionals because increased water temperatures threaten coldwater species (McCullough et al 2009 ), including those targeted by recreational and commercial fi sheries and species that help to maintain ecological integrity (Isaak et al 2012 ;Lee et al 2020 ). For example, modeling demonstrates that Chinook Salmon Oncorhynchus tshawytscha Gaines et al 2022 ), fi shery (Miller et al 2010 ;Holsman et al 2019 ), and watershed (Chichakly et al 2013 ;Makino et al 2021 ) management, as well as hydropower operations and licensing (Viers 2011 ;Rheinheimer et al 2013 ;Uncommon Dialogue 2020 ;Heggenes et al 2021 ).…”