Drawing together multiple lines of evidence from assessment studies of hydropeaking pressures in impacted rivers

Abstract

Hydropeaking has negative effects on aquatic biota, but the causal relationships have not been studied extensively, especially when hydropeaking occurs in combination with other environmental pressures. The available evidence comes mainly from case studies demonstrating river-specific effects of hydropeaking that result in modified microhabitat conditions and lead to declines in fish populations. We used multiple lines of evidence to attempt to strengthen the evidence base for models of ecological response to flow alteration from hydropeaking. First, we synthesized evidence of ecological responses from relevant studies published in the scientific literature. We found considerable evidence of the ecological effects of hydropeaking, but many causal pathways are poorly understood, and we found very little research on the interactive effects of hydropeaking and other pressures. As a 2 nd line of evidence, we used results from analyses of large-scale data sets. These results demonstrated the extent to which hydropeaking occurs with other pressures, but did not elucidate individual or interactive effects further. Thus, the multiple lines of evidence complemented each other, but the main result was to identify knowledge gaps regarding hydropeaking and a consequent pressing need for novel approaches, new questions, and new ways of thinking that can fill them.

Life Stage-Specific Hydropeaking Flow Rules

“…Therefore, there is a need to develop qualitative seasonal flow rules for hydropeaking rivers as well. Here, we focused solely on salmonid species as most available literature deals with this fish family [15,17,18]. Many aspects of the presented framework can potentially be transferred to other taxa as well, but further research must be conducted on other fish families, such as cyprinids, to validate these suggestions.…”

“…We, therefore, describe the impacts of hydropeaking on each life cycle stage and propose critical aspects which must be considered when defining mitigation rules. We focus on salmonid fish as they are the most studied and most affected fish family regarding hydropeaking [17,18]. Nevertheless, many aspects of the presented mitigation concept can potentially be transferred to or adapted to the requirements of other taxa.…”

Seasonal effects of a hydropeaking dam on a downstream benthic macroinvertebrate community

“…Lower turbidity values downstream of the dam are likely due to the loss of suspended load in the reservoir. These changes highlight how additional physical alterations to river habitat resulting from hydropeaking can consequently affect water quality and, ultimately, the biotic community (Melcher et al, ).…”

“…Although literature on the effects of hydropeaking on river biota is becoming more common (e.g., Jones, ; Kennedy et al, ; Melcher et al, ), the macroinvertebrates in many studies are collected in late summer or early autumn. In doing so, it is probable that many emergent insect species are not accounted for and thus any effects of hydropeaking on these taxa remain unknown.…”

Consistent but secondary influence of hydropeaking on stream fish assemblages in space and time

“…Hydropeaking corresponds to rapid artificial flow fluctuations downstream of hydropower plants, designed to address sub-daily peaks in electricity demand. Hydropeaking management concerns a large number of dams and river reaches (e.g., 144 of about 600 large dams in France and around 800 km of rivers in Austria; Lauters 1995;Metcher et al 2017), a number expected to increase with the development of renewable energies (IPCC 2011). The flow regime (e.g., flow magnitude, timing and rate of change, frequency and duration of extreme flow events) is strongly modified downstream of hydropeaking power plants, with more rapid and frequent flow variations than occurring naturally.…”