Abstract
Rivers regulated by dams display several ecosystem alterations due to modified flow and sediment regimes. Downstream from a dam, ecosystem degradation occurs because of reduced disturbance, mostly derived from limitations on flow variability and sediment supply. In the last decade, most flow restoration/dam impact mitigation was oriented towards the development of environmental flows. Flow variability (and consequent disturbance) can be reintroduced by releasing artificial high flows (experimental floods). Flow-sediment interactions during experimental floods represent strong ecosystem drivers, influencing nutrient dynamics, and metabolic and functional properties. In river networks, sediment and water inputs from tributaries generate points of discontinuity that can drive major changes in environmental conditions, affecting habitat structure and determining functional differences between upstream and downstream. However, despite the relevance for management, flow/sediment relations during environmental flows − and more importantly during experimental floods − remain poorly understood, mostly due to the lack of empirical evidence. In this study, we examined how a major tributary (source of water and sediments) modified the physical habitat template of a regulated river, thereby influencing ecological and geomorphological responses to experimental floods. Methods combined high-resolution drone mapping techniques with a wide range of biological samples collected in field surveys before, during, and after experimental floods in an alpine river. Data were used to quantify changes in relevant functional and structural ecosystem properties, relating ecological responses to geomorphological dynamics. Results highlight the importance of tributaries in restoring ecosystem properties lost after damming, enhancing the resilience of the system. In addition, we observed that disturbance legacy played a fundamental role in determining ecological conditions of a river prior to experimental floods, thus confirming that considering flow variability and sediment availability is crucial in adaptive dam management and environmental flows design.
Highlights
A rivers’ natural flow regime is characterized by fluctuations in discharge between low flows/droughts and high flows/floods, tightly coupled with precipitation/snowmelt events, generally with some de gree of seasonal predictability (Poff et al, 1997)
Due to the eco-morphological impacts caused by the dams, a board composed of members of the Swiss National Park, the hydropower company Engadiner Kraftwerke (EKW), Federal and Cantonal authorities agreed to an experimental flood program starting in 2000
As drift density and taxa richness were comparable between floods, we suggest that macroinvertebrates were present at similar densities as found before the earlier flood (2018), (Table 1), but likely distributed mostly in refugia habitat
Summary
A rivers’ natural flow regime is characterized by fluctuations in discharge between low flows/droughts and high flows/floods, tightly coupled with precipitation/snowmelt events, generally with some de gree of seasonal predictability (Poff et al, 1997). Specific life-history traits allow stream and terrestrial organisms to benefit from floods – and low flow windows between floods (Lytle and Poff, 2004; Poiani, 2006), as well as providing resistance and resilience to extreme events (e.g., Robinson, 2012). Many aquatic organisms rely on floods for reproductive or dispersal cues (e.g., Jimenez-Segura et al, 2010), and fish spawning and fry-rearing habitats are in many cases dependent on the seasonal pulse of floods (Chapman, 1988; Junk et al, 1989; Melis, 2011)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
