PNNL

Abstract

Regulated flow regimes with reduced inter-annual flow variability and heightened sub-daily flow variability impact numerous downstream abiotic and biotic conditions including sediment and substrate, temperature, water chemistry, macroinvertebrate community composition, and riparian zone linkages (Antonetti et al., 2022; Hauer et al., 2018; Lagarrigue et al., 2002; Pulg et al., 2016). The direct effects of sub-daily flow variability on fish ecology in regulated rivers is of particular interest to researchers given the need to balance the cultural, economic, and recreational value of fisheries resources with the ability of flexible hydropower production to help meet global energy decarbonization goals. Fish responses to sub-daily flow variability can be investigated as acute reactions to specific hydropeaking phases (e.g., stranding during down-ramping events) or as the cumulative result of chronic exposure to highly unstable environments (e.g., community composition between natural and regulated systems) using techniques ranging from laboratory experiments to field observations to model simulations. Previous reviews of relationships between hydropower production, flow regimes, and fish ecology have been restricted to specific groups of fishes (Hunter, 1992), life stages (Hayes et al., 2019), or ecological outcomes (Harper et al., 2022; Nagrodski et al., 2012; Rytwinski et al., 2020). Consequently, there is a need for a systematic review to synthesize known relationships between hydropower flexibility and fish ecological outcomes, characterize typical approaches and metrics used to study these relationships, and identify opportunities for future research directions. Flexible hydropower can help support increased integration of variable renewable energy into global power grids as we look to decarbonize the power sector. However, flexible operation of hydropower dams dramatically alters downstream flow regimes with potentially severe consequences for aquatic ecosystems. Therefore, it is critical that we understand the relationship between sub-daily flow variability created by flexible hydropower production and fish ecological outcomes in downstream lotic environments to identify potential tradeoffs between power grid stability and ecological integrity and inform hydropower policy (Roni et al., 2023). Accordingly, we conducted a systematic review of the ecological effects of sub-daily flow variability due to hydropower production on global riverine fishes.