The effects of weirs on structural stream habitat and biological communities

Abstract

Summary1. Most of the world's rivers are affected by dams and weirs. Information on the quantitative and qualitative effects of weirs across biological communities is crucial for successful management and restoration of stream ecosystems. Yet, there is a lack of comprehensive studies that have analysed the serial discontinuity in direct proximity of weirs including diverse taxonomic groups from algae to fish. 2. This study compared the abiotic stream habitat characteristics upstream and downstream of weirs as well as their effects on the community structure of periphyton, aquatic macrophytes, macroinvertebrates and fish at five different study rivers. 3. Physicochemical habitat characteristics discriminated strongly between upstream and downstream sides of weirs in terms of water depth, current speed, substratum composition and the transition between free-flowing water and interstitial zone. Accordingly, abundance, diversity, community structure and functional ecological traits of all major taxonomic groups were indicative of serial discontinuity, but the discriminative power of individual taxonomic groups strongly differed between rivers. 4. The simultaneous inclusion of abiotic habitat variables, taxonomic diversity and biological traits in multivariate non-metric multidimensional scaling was most comprehensive and powerful for the quantification of weir effects. In some cases, the intrastream discrimination induced by weirs exceeded the variation between geographically distant rivers of different geological origin and drainage systems. Community effects were generally detectable on high levels of taxonomic resolution such as family or order level. 5. Synthesis and applications. River sections in spatial proximity to weirs are affected seriously and should be included in the ecological assessments of the European Water Framework Directive. Multivariate models that include several taxonomic groups and physicochemical habitat variables provide a universally applicable tool for the ecological assessment of impacts on serial discontinuity and other stressors on stream ecosystem health.

Run-of-River hydropower and salmonids: potential effects and perspective on future research

“…The second mechanism by which a reduction in flow from RoR hydropower operations could impact fish is through a reduction in habitat quantity and diversity (Anderson et al 2006;Baker et al 2011;Mueller et al 2011). Overall, the literature demonstrates that the diversion of flow in streams reduces the depth and velocity of water in bypassed reaches, which generally leads to a decline in habitat quantity and quality and, in turn, to a decline in fish biomass and density.…”

“…The creation of headponds inundates riparian areas and fundamentally interrupts the NFR in reaches immediately upstream of low-head dams by reducing flow variability, velocity, and turbulence and increasing the deposition of fine sediment (Csiki and Rhoads 2010;Butler and Wahl 2011). Such changes in physical habitats can lead to impacts on riverine ecosystems by reducing water quality and altering the abundance, richness, and composition of periphyton, invertebrate, and fish assemblages (Santucci et al 2005;Mueller et al 2011;Anderson et al 2014). In contrast, the flow regime in reaches downstream of RoR powerhouses is expected to be the most similar to the NFR, since water diverted for power generation is returned to rivers after passing through turbines (Poff and Hart 2002;Kibler and Tullos 2013;Senay et al 2016).…”

Chemical variability of water and sediment over time and along a mountain river subjected to natural and human impact

“…Recently, more attention has focused on the impact of small dams or weirs on biocoenosis, which is important for successful management and restoration of stream ecosystems. Mueller et al (2011) found that weirs, through the changes in the physical habitat characteristics such as water depth, current speed, substratum composition and the transition between free-flowing water and interstitial zone upstream and downstream of the barrier, disturb the continuity of communities of the taxonomic groups of periphyton, macrophytes, macroinvertebrates and fish. Sharma et al (2005) and Martínez et al (2013) documented the impact of weirs on changes in physical characteristics of habitat and of benthic invertebrate communities.…”

“…The effects of barriers on the ecological integrity of various European rivers have been intensively studied (Koster and Crook, 2008;Kemp and O'Hanley, 2010;Mueller et al, 2011;Rolls, 2011;Rolls et al, 2014, Sondermann et al, 2015Perkin et al, 2015), obtaining information which is crucial for the successful restoration of river ecosystems. Recently, more attention has focused on the impact of small dams or weirs on biocoenosis, which is important for successful management and restoration of stream ecosystems.…”

Influence of abiotic factors on invasive behaviour of alien speciesElodea nuttalliiin the Drava River (Slovenia)

“…Information on the quantitative and qualitative effects of these structures on biological communities is crucial for successful management and restoration of stream ecosystems (Mueller et al, 2011). Impoundment of a river causes the carrying power of its flow to diminish and deposit of sediments (silt and clay) begins, creating environments that favour development of macrophytes.…”