Abstract
Removal of lateral constraints to restore rivers has become increasingly common in river resource management, but little is known how the interaction of de-channelization with flow influences ecosystem structure and function. We evaluated the ecosystem effects of river widening to improve sediment relations in the Thur River, Switzerland, 12 years after implementation. We tested if restored and non-restored reaches differed in water physico-chemistry, hyporheic function, primary production, and macroinvertebrate density and composition in relation to the flow regime. Our results showed that (i) spatio-temporal variation in sediment respiration and macroinvertebrate taxonomic richness were driven by interactions between restoration and flow; (ii) riverbed conditions including substrate size, organic matter content, and groundwater–surface water exchange changed due to restoration, but (iii) physico-chemistry, hydraulic conditions, and primary production were not altered by restoration. Importantly, our study revealed that abiotic conditions, except channel morphology, changed only marginally, whereas other ecosystem attributes responded markedly to changes in flow-restoration interactions. These results highlight integrating a more holistic ecosystem perspective in the design and monitoring of restoration projects such as river widening in resource management, preferably in relation to flow-sediment regimes and interactions with the biotic components of the ecosystem.
Highlights
Flow regime is a principal driver of riverine ecosystems [1,2,3], maintaining habitat conditions and connectivity, and influencing flora and fauna [4,5,6,7]
Flow and sediment regimes mutually interact, as streamflow transports sediment, and river morphology formed by sediment transport determines hydrodynamics
We investigated the effect of channel protection removal on ecosystem structure and function after 12 years in the Thur River, Switzerland
Summary
Flow regime is a principal driver of riverine ecosystems [1,2,3], maintaining habitat conditions and connectivity, and influencing flora and fauna [4,5,6,7]. Sediment regime sustains riverine ecosystems [8], driving channel morphology and riverbed heterogeneity, and structuring aquatic and riparian communities [9,10,11,12]. Flow and sediment regimes mutually interact, as streamflow transports sediment, and river morphology formed by sediment transport determines hydrodynamics. Both regimes and their interaction play a decisive role in maintaining habitat structure and ecosystem. Longitudinal and latitudinal connectivity of water and sediment is dramatically reduced by dams, weirs, and levees, decreasing the physical complexity (ecosystem homogenization) of river channels [15,16]. Human interventions have severely modified flow and sediment regimes in rivers with concomitant impacts on resident biota
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