Effects of water level regulation in alpine hydropower reservoirs: an ecosystem perspective with a special emphasis on fish

Abstract

Sustainable development of hydropower demands a holistic view of potential impacts of water level regulation (WLR) on reservoir ecosystems. Most environmental studies of hydropower have focused on rivers, whereas environmental effects of hydropower operations on reservoirs are less well understood. Here, we synthesize knowledge on how WLR from hydropower affects alpine lake ecosystems and highlight the fundamental factors that shape the environmental impacts of WLR. Our analysis of these impacts ranges from abiotic conditions to lower trophic levels and ultimately to fish. We conclude that the environmental effects are complex and case-specific and thus considering the operational regime of WLR (i.e., amplitude, timing, frequency, and rate of change) as well as the reservoir's morphometry, geology and biotic community are prerequisites for any reliable predictions. Finally, we indicate promising avenues for future research and argue that recording and sharing of data, views and demands among different stakeholders, including operators, researchers and the public, is necessary for the sustainable development of hydropower in alpine lakes.

Ecological impacts of winter water level drawdowns on lake littoral zones: a review

“…These gaps arise from the limited scope of most drawdown studies, which typically only include a small number of lakes, limited years, and limited response variables. Here, we identify eight key research needs; several of these are aligned with a recent review by Hirsch et al (2017) on water level fluctuation impacts in hydropower reservoirs. Given that lake ecosystems are increasingly stressed by humans and winter drawdowns are one of the few tools available to address nuisance macrophytes (and other tools such as herbicides and mechanical harvesting have different potential impacts on lakes), increased understanding of impacts of lake drawdowns is critical to compare ecosystem consequences of different management approaches.…”

“…Additional abiotic factors may alter the extent of effects of drawdowns, including geology (bed texture, chemistry), climate (e.g., precipitation and ice cover), lake trophic status, and time since reservoir creation (see Hirsch et al 2017). For example, mesotrophic and eutrophic shallow lakes may be more susceptible to changes in ecosystem states (clear-water to turbid) with drawdowns, whereas effects on deep, stratified lakes may be limited to littoral zones except with deeper drawdowns.…”

“…Despite an increase in research on water level fluctuations since the early 1990s, research on winter drawdowns remains limited and needs an updated synthesis. Recent review papers focus on the influence of regulated water level fluctuations on shallow lakes and wetlands (Coops et al 2003), stratified lakes (Zohary and Ostrovsky 2011), lakes in general (Leira and Cantonati 2008), and alpine hydropower reservoirs (Hirsch et al 2017). Previous reviews specific to winter drawdowns include Cooke (1980), Ploskey (1983), Wilcox and Meeker (1992), and most recently by Cooke et al (2005) and Abrahams (2006) with a specific focus on macrophyte management.…”

Integrating Economic and Ecological Benchmarking for a Sustainable Development of Hydropower

“…The most pertinent effects of hydropower on reservoir and lake ecosystem functions are water level fluctuations (WLF) (Hirsch et al, submitted [10]). WLF profoundly affect the ecosystem of natural lakes [11,12], but WLF have even more profound effects in reservoirs because WLF in reservoirs typically exceed natural fluctuation three-to ten-fold in frequency and amplitude [5,12].…”

Annual winter water level drawdowns limit shallow‐water mussel densities in small lakes

“…composition, distribution, and abundance) and function (reviewed by Carmignani & Roy, 2017;Hirsch et al, 2017). composition, distribution, and abundance) and function (reviewed by Carmignani & Roy, 2017;Hirsch et al, 2017).…”