International Review of Hydrobiology最新文献

The majority of rivers in Europe has been dramatically altered in terms of their morphology and hydrology with severe consequences for the diversity and ecological functioning of the rivers and their floodplains. Consequently, an increasing number of river reaches has been restored over the past decades, often including the removal of bank fixation to reinitiate bank erosion and allowing for a rewidening of the rivers' cross-section. However, monitoring in detail the effect of such a measure on riverine vegetation is scarce. Using a Before-After-Control-Impact (BACI) design, we analysed the early changes of the vegetation 2 years after the removal of bank fixation at the Mulde River (central Germany). The results were compared with two types of control sites, representing a nonrestored as well as a natural riverbank that has never been fixed. We analysed differences in taxonomic and functional composition of the vegetation between bank types as well as community turnover after restoration. Two years after restoration, the vegetation differed clearly from the nonrestored sites. A substantial proportion of the community, especially the newly established species, became more similar to the natural bank community. Most importantly, spatiotemporal heterogeneity of the vegetation increased after removal of bank fixation, being an indicator for re-established dynamic processes similar to the natural site. The presented data serve as a baseline for a long-term monitoring and quantitative meta-analysis of restoration effects.

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 side-arm) 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.

The concept of ecosystem services (ES) is a powerful tool for communicating with stakeholders because it highlights the benefits of ecosystems for people and demonstrates their economic importance through monetized values. However, this hypothesis has rarely been substantiated in the context of local landscape planning. To investigate which ecosystem services information formats (ESIF) stakeholders prefer in decision situations, we experimented with a highly conflictual planning situation about the Lower Mulde restoration in Germany. We invited local stakeholders to a so-called ‘future vision workshop’. It included a paper-based, noncompetitive planning game, which combined the freedom of choice with strict rules for justifying the proposed measures. We tested how often participants used different ESIFs to justify their decisions, focusing on quantification, monetization, and the default qualitative (ordinal-scaled) format applied in landscape planning. A total of 17 representatives from stakeholder groups such as nature conservation, recreation, and local politics attended. We provided information on four ES and eight related measure proposals to the stakeholders, who used them to select, locate, and justify actions for the area's future development. The participants applied the ordinal-qualitative format in more than two-thirds of the decisions. Quantification and monetization were used with approximately equal frequency, mostly for measures that favoured flood risk regulation. Actions supporting habitat provision and biodiversity were justified exclusively in ordinal-qualitative terms. Instead of our provided quantifications, some participants mentioned numbers they were already familiar with before. They also partly doubted our monetization approaches. In conclusion, we recommend combined and context-specific uses of several ESIFs, while using the ordinal-qualitative format as the basis. Furthermore, the participants appreciated the workshop and requested that the results be presented to the city council. The workshop also confirmed that the ES concept is challenging to understand, especially for laypeople unfamiliar with ES and landscape planning.

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 near-natural 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.

Restoring natural fluvial dynamics is fundamental for sustaining biodiversity and functional integrity of river and floodplain ecosystems. In Central Europe, however, pervasive river regulation and bank protection have greatly impaired ecosystem functioning and many water bodies fail to achieve a good ecological status within the European Water Framework Directive. The “Free Moving Rivers” approach seeks to restore the ecological integrity of rivers and floodplains by creating appropriate conditions for natural fluvial dynamics. Principal goals of the approach include removing artificial constraints on river processes and expanding the river corridor to restore natural river habitats and structures. Lacking, however, are complementary tools that evaluate and predict changes to ecosystem services (ESSs) after implementation. Here, we describe a case study of the Ammer river in Bavaria, Germany, to (i) calculate the extent of the “Free Moving Rivers” corridor, and (ii) assess changes to ESSs of a proposed river restoration measure under two alternative land-use scenarios. To do this, we apply the River Ecosystem Service Index (RESI), whereby individual ESSs are assessed in a spatially explicit way. We show how a proposed implementation of the “Free Moving Rivers” approach enhances three investigated ESSs: flood retention, sediment balance and habitat provision. We conclude that RESI is a potentially useful tool with wide applicability for restoration planning that synthesises floodplain complexity in such a way that facilitates decision making.

Spring helocrenes are a unique aquatic environment with high biotic diversity. Although environmental heterogeneity has traditionally been assumed to explain the high species richness of spring habitats, this assumption has never been properly tested. Here, we sampled macroinvertebrates from two calcareous helocrenes in Slovakia with visually distinguishable mesohabitat heterogeneity. We hypothesise that macroinvertebrate beta diversity significantly increases with environmental heterogeneity even at a small within-site spatial scale. We also examined four species-trait categories, that is, active or passive dispersers and habitat specialists or generalists. Significant spatial structuring of environmental heterogeneity was found at one site, whereas the other site did not show a clear spatial pattern. Strong associations were found between beta diversity of all species trait categories and environmental heterogeneity at the first site, while there were virtually no associations at the second site. Specialists were not spatially structured at any of the sites examined. Our results suggest that invertebrate beta diversity responds positively to environmental heterogeneity at a site by also tracking spatial structuring of abiotic conditions. However, the response may vary depending on the dispersal mode and habitat specialisation of the invertebrates.

Large wood (LW) is an integral part of natural river ecosystems and determines their ecological integrity by modulating hydromorphology and providing habitats. Hence, LW installations are a common restoration measure in large rivers, even if effects on biodiversity are ambiguous or unknown for ecosystem functioning. Here we quantified the hydromorphological, biological, and functional effects of LW 8 months after installation in a large gravel-bed river. Both morphological and flow diversity increased strongly by 821% and 127%, respectively. Similarly, fish abundance increased nearly 10-fold, and macroinvertebrate diversity increased by 35%. Ecosystem functions benefited from LW installation and increased significantly (e.g., by up to 390% for bacterial production) at sites influenced by LW compared to those without LW. Our results highlight the role of the bark habitat of LW that increased the direct effects of LW via the provision of new habitat and stimulated ecosystem-wide processes. Our integrative approach evaluating the success of LW installations in a large river revealed cascading effects from the provisioning of new habitats, the increase of species diversity to higher ecosystem functioning. It also demonstrated that hydromorphological parameters or community composition alone are insufficient to quantify the complex effects of LW installation, which underlines the necessity to evaluate restoration success with different measures.

Large wood structures, such as wood fragments, debris jams, or entire trees, create flow and habitat diversity in rivers. A key flow feature associated with such structures is the wake, characterised by a core zone of reduced velocity and shear layers at its margins. Wakes are largely controlled by geometric and structural properties of the wood. In the present study, the flow patterns and turbulence created by different wood structures were compared at two study sites: naturally eroded and fragmented oaks (Site A) and artificial poplar installations (Site B). Flow and turbulence were quantified using pointwise velocity measurements with acoustic Doppler velocimeters (ADVs) and surface particle tracking velocimetry (SPTV). The measured flow patterns exhibited similarities with shallow porous wakes that feature fluid advection through the structure into the wake core downstream. Two additional features of wood structures were identified in the present study: (i) the growth of the shear layers was hindered by bed friction like for shallow mixing layers and (ii) the presence of a tree stem and sediment deposit in the wake centre delayed or even suppressed the interaction of the shear layers and vortex street formation similar to a wake-splitter plate. Methodologically, the combined ADV/SPTV measurement approach and the use of analytical models for shallow mixing layers proved to be highly valuable to decipher the complex flow patterns around wood structures in the field.

Riverbanks are very dynamic habitats for riparian vegetation strongly influenced by fluvial and geomorphic processes. This habitat type was severely reduced in the past by river straightening and bank stabilisation. Restoration and establishment of new floodplain streams promote this habitat, but a directed succession to later stages was observed many times. Our study aimed to analyse whether the often observed directed succession of the streambank vegetation after restoration implementation could be reversed by a natural flood along a newly created floodplain stream. We investigated the effects of a natural flood in 2013 and different prerestoration conditions on species development in the riparian zone. Vegetation was studied along 12 transects in four different sections from 2011 to 2014. Species composition differed strongly between the sections. Species richness was lowest in a newly dug steep section with high morphological dynamics and highest on wider flat streambanks. Changes during the years reflecting different hydrological events varied between sections. The high natural flood in 2013 reduced the cover of the herb layer and increased bare ground, which led in most sections to a loss of nontarget species. Total target species richness did not change due to the natural flood, while target species showed a high turnover rate. In the following year, however, the flood-induced development of species composition, in general, was reversed. Natural floods changed abiotic and biotic conditions along the streambank, but they did not accelerate ecological restoration towards predefined target ecosystems. However, they were necessary to preserve the needed dynamic vegetation changes and species turnover to hinder the succession to later stages dominated by a few species. Our study shows that riparian vegetation near the streambank can be monitored most effectively in cross-profile transects, both in the long-term and event-related.