Over the last 40 years, a growing number of restoration projects have been implemented to improve the ecological conditions of highly degraded rivers and their floodplains. Despite considerable investment in these projects, information is still limited about the effectiveness and the success of such river restoration measures, mainly due to a lack of standardised and interdisciplinary assessment approaches.During the project 'Wilde Mulde-Restoration of a dynamic riverine landscape in Central Germany', we implemented hydromorphological restoration measures (installation of large wood, removal of rip-rap, reconnection of a former river sidearm) along a lowland river in Central Germany. We carried out intensive scientific monitoring of biodiversity, hydromorphology, ecosystem functions and services, as well as socio-economic aspects. A Before/After-Control/Impact (BACI) design was used to identify the spatial and temporal effects of the restoration measures and to distinguish them from changes caused by background variation. For this, we used a comprehensive set of indicators, including abiotic (flow velocity, diversity of riverbed topography, and flow resistance), biological (ecosystem respiration, macroinvertebrates, fish, carabids, vegetation, and birds) and socio-economic (acceptance and public awareness) indicators as well as the ecosystem service indicator aesthetic quality of the landscape. To meet the inherent challenges of such a large-scale field experiment, like unpredictable environmental conditions, we used an experimental approach that allowed us to demonstrate a measurable success of the implemented restoration measures. The majority of the abiotic and some of the biological and socio-economic indicators at the restored sites approached values of a natural reference site while already deviating from values of a nonnatural reference site two years after restoration. In addition to the applied interdisciplinary approach, multiple scales of field investigations and data analyses are essential as key components for evaluating successful river and floodplain restoration projects.

Near-natural rivers and riparian ecosystems can represent biodiversity hotspots harbouring many highly specialised, rare and endangered species. During the past centuries, these habitats have been heavily degraded by anthropogenic use, and therefore river restoration is one of the most striking fields of action that is legally defined by the European Union Water Framework Directive. Successful restoration depends on realistic and specified targets that should be defined beforehand and founded on status quo surveys. We present a comparison of carabid beetle communities in riparian habitats of natural and managed river sites of the Mulde River in the Biosphere Reserve Middle Elbe. This endeavour is part of a unique multi-level revitalisation project. Pitfall trapping in 2016 and 2017 yielded 111 carabid species with many species of conservation concern in natural and managed habitats. However, Simpson diversity and functional diversity were lower in the latter. Both habitats harboured specific species assemblages with characteristic indicator species. Additionally, the trap location on slip-off slopes or cut banks was a significant driver of species composition. Our results indicate high ecological development potentials for the Mulde River, but restoration should consider differences between slip-off slopes and cut-off banks. We postulate that future restoration will foster population increases as well as a wider distribution of rare and endangered riparian habitat specialists.

Natural rivers offer riparian habitats to many highly specialised, rare, and endangered insect species and are extremely important for ecosystem services. In the past, these ecosystems have been heavily degraded by anthropogenic use and run the risk of losing their favourable ecological conditions. For this reason, restoration measures are urgently needed and strongly demanded politically as well as legally, for instance, through the European Union Water Framework Directive. This is also important because nowadays, we are confronted with increasing insect declines.Using a Before-After-Control-Impact approach, we studied the effects of a riverbank restoration (complete removal of a large gravel embankment) on carabid assemblages of riparian habitats along the Mulde River in central Germany in 2017 and 2019. We collected 86 species in three site types (managed, natural, and restored) by pitfall trapping and found numerous species of conservation concern. Our analyses showed that the percentage of species of conservation concern was significantly higher after restoration in restored compared to managed sites. Furthermore, after restoration, the percentage of indicator species for natural sites increased significantly in restored sites while the abundance of indicator species characteristic for managed sites decreased in these sites. Species assemblage composition significantly changed in response to restoration approaching nearnatural conditions. The creation of habitat mosaics with open gravel and sand patches as well as the re-establishment of river dynamics were likely the most significant drivers for restoration success. We were able to show how important the restoration of riparian habitats is to promote populations of endangered, rare, and specialised species. Our results highlight that positive effects of a river restoration measure can be observed after a relatively short time. Ground beetles can thus be viewed as early indicators for restoration success, but we see a need for long-term monitoring to evaluate long-term effects reliably.

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