Abstract
Abstract. River restoration can enhance river dynamics, environmental heterogeneity and biodiversity, but the underlying processes governing the dynamic changes need to be understood to ensure that restoration projects meet their goals, and adverse effects are prevented. In particular, we need to comprehend how hydromorphological variability quantitatively relates to ecosystem functioning and services, biodiversity as well as ground- and surface water quality in restored river corridors. This involves (i) physical processes and structural properties, determining erosion and sedimentation, as well as solute and heat transport behavior in surface water and within the subsurface; (ii) biogeochemical processes and characteristics, including the turnover of nutrients and natural water constituents; and (iii) ecological processes and indicators related to biodiversity and ecological functioning. All these aspects are interlinked, requiring an interdisciplinary investigation approach. Here, we present an overview of the recently completed RECORD (REstored CORridor Dynamics) project in which we combined physical, chemical, and biological observations with modeling at a restored river corridor of the perialpine Thur River in Switzerland. Our results show that river restoration, beyond inducing morphologic changes that reshape the river bed and banks, triggered complex spatial patterns of bank infiltration, and affected habitat type, biotic communities and biogeochemical processes. We adopted an interdisciplinary approach of monitoring the continuing changes due to restoration measures to address the following questions: How stable is the morphological variability established by restoration? Does morphological variability guarantee an improvement in biodiversity? How does morphological variability affect biogeochemical transformations in the river corridor? What are some potential adverse effects of river restoration? How is river restoration influenced by catchment-scale hydraulics and which feedbacks exist on the large scale? Beyond summarizing the major results of individual studies within the project, we show that these overarching questions could only be addressed in an interdisciplinary framework.
Highlights
Over the last 20 years, revitalization of engineered river reaches has been established in Europe as a measure towards achieving a good ecological status of water bodies as required by the EU Water Framework Directive (European Commission, 2000) while protecting downstream river reaches from floods
Within the project’s broad objectives, we focused on concepts integral to river restoration and in particular reported on the modification of a section of the Thur River, Switzerland (Pasquale et al, 2011; Schneider et al, 2011), Figure 2
We argue that the same sort of natural observatories and scientific networks are required to gain a holistic understanding of river restoration and the interrelated physical, chemical, biological and ecological processes
Summary
Over the last 20 years, revitalization of engineered river reaches has been established in Europe as a measure towards achieving a good ecological status of water bodies as required by the EU Water Framework Directive (European Commission, 2000) while protecting downstream river reaches from floods. Our studies on pioneer vegetation with subsequent development of river bars and islands, as well as our investigations on soil processes including carbon and nitrogen cycling would not have been possible in such a comprehensive way if we had not had temporally and spatially highly resolved information on river flow and water level data The latter information, together with the detailed 3-D geophysical images of the subsurface, was crucial to construct a 3-D groundwater flow and transport model with a highly dynamic river boundary condition. 2.2 Biogeochemistry: dynamics of organic carbon, nutrients and pollutants in groundwater and floodplain soils For these investigations and the biological studies described, we transferred the FPZ concept, introduced by Thorp et al (2006) for the catchment scale, to the scale of a single reach and extended the concept of “functional” to ecological processes in addition to physical functioning of geomorphic and hydrologic forces (Samaritani et al, 2011). The information on flow dynamics and flow paths in the aquifer adjacent to the river provided by the 3-D flow and transport model (Diem et al, 2014) was pivotal to drawing conclusions about differences in degradation rates between the restored and the channelized section and their possible causes
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