Abiotic Characterization of Brown Trout (<i>Salmo trutta f. fario</i>) and Rainbow Trout (<i>Oncorhynchus mykiss</i>) Spawning Redds Affected by Small Hydropower Plants - Case Studies from Austria

Small run-of-river hydropower plants (RRHPs) have revealed strong harmful effects worldwide on stream habitats (e.g., fragmentation and destruction) and decreased fish species, especially anadromous species abundance. Recently, RRHPs have rapidly been installed in Serbia. Most were installed on montane streams because their steep slopes are most convenient for hydropower energy production at minimal costs.Brown trout Salmo trutta are prominent in the fish communities of this rarest type of aquatic ecosystems. Their native molecular diversity reflects a biodiversity hotspot in the Balkans, and they provide attractive fishing opportunities. Records from fishery management plans for highland stream fisheries where RRHPs were installed revealed reduced brown trout biomass compared with streams without RRHPs.Research on six streams with operational RRHPs revealed severe deterioration of habitat, for example, increased water temperature, reduced dissolved oxygen, and increased nutrient contents. Effects on fish communities were evident from a change in their structure. Resident, stream-dwelling brown trout were the most affected species with steep declines in abundance, biomass, and productivity. Fragmentation owing to damming was also reflected by deterioration of their age structure. Unique native brown trout stocks susceptible to adverse effects are difficult to restore by stocking, and fish passages commonly supplied as compensation to overcome the disruption of habitats cannot mitigate the threat posed to the fish.

Section: Resultssupporting

confidence: 92%

Effects of run‐of‐river hydropower plants on fish communities in montane stream ecosystems in Serbia

Simonović

Ristić

Milčanović

et al. 2021

“…(e) Therefore, dams and reservoirs change local taxonomic structure and composition depending on their size and operations, including the increased prevalence of non‐native invasive species (Hughes, Rinne, & Calamusso, ; Johnson, Olden, & Vander Zanden, ; Linares, Callisto, & Marques, ; Terra & Araujo, ; White, ). Importantly, studies on these ecological impacts are mainly based on large dams (e.g., Agostinho, Pelicice, & Gomes, ; Horsák, Bojková, Zahrádková, Omesová, & Helešic, ; Martins et al, ), whereas information about the ecological consequences of small hydropower dams is largely lacking (e.g., Anderson, Moggridge, Shucksmith, & Warren, ; Mbaka & Wanjiru Mwaniki, ; Obruca & Hauer, ; Wang, Chen, Liu, & Zhu, ).…”

Section: Introductionmentioning

confidence: 99%

Small hydropower dam alters the taxonomic composition of benthic macroinvertebrate assemblages in a neotropical river

Linares

Assis

Solar

et al. 2019

Hydropower dams substantially modify lotic ecosystems. Most studies regarding their ecological impacts are based on large dams and provide little information about the far more abundant effects of small hydropower dams. Our aim was to characterize the ecological effects of a small hydropower dam and run-of-the-river reservoir on the structure of benthic macroinvertebrate assemblages in the Pandeiros River located in the neotropical savanna of Brazil. We tested the hypothesis that benthic macroinvertebrate assemblages in sites directly affected by the dam and reservoir would show a different taxonomic structure compared with those in free-flowing sites. We expected to find sensitive native species associated with the free-flowing sites, whereas resistant and non-native invasive taxa were expected in impounded sites. We also explored associations between the presence of native and nonnative invasive taxa to each habitat type. We found that the structure of benthic macroinvertebrate assemblages was significantly different between free-flowing and impounded sites. Also, we found that the dam and reservoir facilitated colonization of non-native invasive species (Corbicula fluminea and Melanoides tuberculata) because only in those sites they were found in high abundance, in contrast to the free-flowing sites. Although the environmental conditions imposed by the impoundment altered the structure of benthic macroinvertebrate assemblages, the effects were limited to sites closest to the dam. Our results highlight the necessity of understanding physical habitat changes caused by the presence and management of run-of-the-river dams and reservoirs.

“…The occasionally low bankfull discharge capacity of these rivers hardly enables the breakup of the surface layer due to the low bed shear stresses, even in terms of exceptional flood events (e.g., with hundred‐year recurrence intervals; Hauer, Unfer, Tritthart, & Habersack, ). Furthermore, suitable spawning gravel ( d = 2–5 cm; Obruca & Hauer, ) deposited in the subsurface layer is limited and largely unavailable for the reproduction of salmonids ( Salmo trutta and Thymallus thymallus ; Hauer et al, ).…”

Section: Introductionmentioning

confidence: 99%

Ripple dynamics over various microtopographical roughness elements and their implications for river management

Hauer

Lichtneger

Holzinger

et al. 2019

Specific problems in connection with the sediment regime have arisen in the granite and gneiss area in the northern part of Austria due to the increased sediment supply of coarse sand and fine gravel as a product of rock weathering. One of the physical characteristics of these sediments is their high mobility in form of ripple bedforms along the surface. In these rivers, the microtopographical structures of the bed surface are hydraulically active, especially in the initial stages when ripples have not overtopped the largest elements of the bed's roughness elements. There is a lack of detailed studies of the impacts of these microtopographical structures on ripple dynamics. Thus, the aim of the present study was to investigate the impact of various microtopographic roughness elements on ripple movement. This study was performed using a 1:1-scaled physical laboratory experiment. The results showed, in all repetitions of the experiment with variable grain sizes, that the higher the microtopographical variability of the river substrate and turbulence was, the higher the measured transport velocities of the ripples were. The expected hidden impacts on sediment transport were not documented. Important implications for sediment management were discussed, as river sections with high accumulation rates of coarse sand and fine gravel are prone to additional degradation as downstream transport decreases over smooth ripple-dune morphologies. Additionally, structural elements such as exposed rocks may increase the downstream transport due to the increased variability in turbulence.