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Geographical location of the tributaries of the lower river Rhine delta in the Netherlands. Restored channels are indicated with open circles (two-sided connected channels) and closed triangles (one-sided connected channels). Letter combinations indicate channel name (see Table 1). Width of individual river branches represents relative annual discharge between 1990 and 2011 and arrows indicate flow direction. Source: discharge level overlay adapted from Dörrbecker (2016).
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The ecological efficacy of river restoration projects may change over time, resulting in the loss of their ecological function for targeted species. The goal of this study was to evaluate the rheophilic nursery function of restored floodplain channels over time, by analysing 30 years of monitoring data from 12 restoration projects in the lower rive...
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Context 1
... river Rhine is the second largest river in Central and Western Europe ( Tockner et al., 2009). It originates in the Alps and flows through Switzerland, Austria, France, Germany and the Netherlands, before it flows into the North Sea. The channel of Opijnen ("OP" in Fig. 2), one of the study locations of this study, was the first major floodplain restoration project in the Netherlands and was constructed in 1994 ( Simons et al., 2001). Since then, 34 water bodies were reconnected with the main river channel through various floodplain restoration programmes. The majority of these restoration projects ...
Context 2
... ( ) in 2009(3) and an extensive study in (overview in Supplementary materials A1 and Stoffers et al., 2020. Sampling strategies for ecological evaluation consisted of monitoring the young-of-the-year (YOY) fish community and characterising habitats. In our evaluation study we included 12 restored channels in the rivers Waal, Nederrijn and IJssel (Fig. 2), which were all sampled at least twice during the 30-year study period (Table 1), resulting in the analysis of 27 sampling events. This selection of data enabled for analysis of the impact of succession in individual floodplain channels on their role as nursery habitat for rheophilic ...
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Sandy beaches, despite of not having a high complexity of habitat, they are used as nurseries by juvenile fishes due to the availability of food. The aim of this work is to study the fish fauna at five beaches on the coast of the Gulf of Cadiz. For this purpose were surveys between December 2016 and November 2017 using a beach seine net in five sam...
Citations
... But conservation and restoration in large lowland rivers tendentially happens within the framework of the socio-economic services that these rivers support (e.g. navigation, flood protection, agriculture, freshwater supply) (Stoffers et al. 2021). Consequently, other-than-human beings' interests and needs usually come second -or are simply disregarded -in mainstream river management. ...
... This alarming trend is due to multiple pressures on freshwater ecosystems including climate change, habitat loss, overharvesting, alien invasive species introductions, intensive agriculture and water pollution [3]. Despite this overall negative trend, recent efforts have been made to restore freshwater habitats (e.g., [4][5][6]) and to set up large scale river restoration programs (e.g., MERLIN, https://project-merlin.eu/, accessed on 22 December 2023). ...
In 2017, the reintroduction of juvenile brown trout in the southwestern part of Flanders (the Zwalm River basin) (Belgium) was initiated. Monitoring during the subsequent years indicated that the released juveniles survived and matured, indicating that sufficient food and good habitat conditions were available. Despite recent fulfilment of free fish migration within the Zwalm River basin and several spawning habitats being present, no natural reproduction of brown trout could be observed. To obtain more insight into the reproduction and maturing of brown trout eggs under natural conditions, an in situ experiment was conducted during 3 consecutive years at 10 different sites within the river basin. The results of our research indicated that egg survival was generally low (<5%). The main causes are most likely a heavy sediment load hampering sufficient oxygen and clean water flow through the redds. In this basin, the sediment load originates mainly from agricultural fields during heavy rain events and consequential run-off. Creating grassy and/or woody buffer strips along watercourses, in combination with changes in agricultural practices, is needed to be able to build up a viable and self-sustaining population of brown trout and also, in a larger context, of other rheophilic fish species.
... Since centuries, European rivers have been fragmented by more than a million physical barriers, altering flow and sediment regimes, and interfering with the movement of organisms (Belletti et al., 2020; Grill et al., 2019). As a result, riverine ecosystems in Europe today lack vital hydromorphological dynamics and have a limited capacity for ecological rejuvenation (Buijse et al., 2005;Stoffers et al., 2021). Finally, both present and future global change will put additional strains on rivers, including warming, intermittency, and the facilitation of the spread of invasive or harmful species. ...
... In any case, assessing restoration efficacy and success is only possible if clear ecological targets and desired outcomes of restoration efforts are defined ahead of time (see Challenge 1). Also, while ecological targets must be set at realistic timelines, monitoring must continue well beyond implementation of a specific set of measures to enable post-hoc adaptive management as crucial means toward the long-term viability of restoration efforts (Stoffers et al., 2021;Thieme et al., 2023). Finally, in line with our plea for the incorporation of meta-ecosystem thinking in riverscape restoration, we advocate for biodiversity-centered monitoring that aims to describe metacommunity processes as indices of integrated connectivity (e.g., Thompson et al. (2020) and Patrick et al. (2021)). ...
The EU Nature Restoration Law represents an important opportunity for freshwater habitat restoration and, consequently, freshwater biodiversity protection. However, a number of challenges must be anticipated in its implementation, which may compromise its success. Some aspects, particularly those relating to freshwater ecosystems, require more clarification. We use riverine ecosystems to illustrate existing ambiguities in the proposed legislation and the potential consequences of leaving these aspects open to interpretation during the implementation process. We also discuss potential solutions to these problems which could help ensure that the law's objectives are met. We argue that river network structure and connectivity dimensions, which result into river meta‐ecosystems, must be explicitly considered. For that purpose, we ask for clear definitions of the critical terms “free‐flowing rivers,” “barriers,” and “reference areas.” In addition, we recommend developing methods for integrated assessment of connectivity across river networks. As a key property of river ecosystems, this must be used to prioritize actions to increase the length and number of free‐flowing rivers. Adequate restoration planning at larger spatial scales will benefit from a meta‐ecosystem perspective and accurate representation of aquatic‐terrestrial linkages, which will significantly improve the efficacy of restoration efforts. Furthermore, stakeholder and citizen engagement offer important opportunities at local, national, and European scales, and should be fostered to ensure inclusive decision‐making. The conservation challenges outlined here are particularly important for rivers, but they also have implications for other ecosystems. These considerations are useful for policymakers, conservationists, and other stakeholders involved in the Nature Restoration Law and related policy initiatives.
This article is categorized under: Water and Life > Stresses and Pressures on Ecosystems
Water and Life > Conservation, Management, and Awareness
Human Water > Water Governance
... Regarding fish responses, restored and reconnected side channels often have greater prevalence of unique and rare species compared to the main channel (Schmutz et al., 2014;Watkins et al., 2015;Whiteman et al., 2011). The abundance and proportion of rheophilic species increased in side channels of the Danube River following restoration (Ramler and Keckeis, 2019), and juvenile rheophilic fishes responded positively to enhanced connectivity of side channels in the Rhine River (Stoffers et al., 2021). ...
... Further, riparian vegetation can create biogeomorphic feedbacks that act to stabilize stream banks, dissipate streamflow energy, and govern landform development (Polvi and Sarneel, 2018) and thus influence the rate of side channel succession. Understanding side channel development processes is important for estimating the longevity and maintenance requirements of side channel restoration and enhancement (Stoffers et al., 2021) as well as the ecological tradeoffs (Marle et al., 2021). ...
... Several recent research projects have tracked side channel restoration and response over time (Ramler and Keckeis, 2019;Stoffers et al., 2022;Stoffers et al., 2021). Monitoring restoration projects that aim to rehabilitate or restore side channels would be informative for design successes and failures. ...
Side channels in large floodplain rivers serve a variety of important ecological roles, particularly in reaches where habitat conditions have been degraded or diminished. We developed hypotheses regarding side channel ecological structure whereby we expected species richness of young of year fishes to generally be higher in shallower, more physically heterogeneous side channels with lower velocities, with differences based on reproductive guild. We also hypothesized species richness of adult fishes to be higher in side channels with greater heterogeneity that could support diverse foraging resources and provide refugia during extreme flow conditions. To test these hypotheses, we used a 28-year fish community dataset from the Upper Mississippi and Illinois Rivers. Across six study reaches, we assessed metrics of side channel physical size, heterogeneity, and connectivity that were hypothesized to explain variance of fish community response, while accounting for site-level factors across 52 side channels using multilevel models. We then used these side channel-level characteristics in a K-means cluster analysis to classify 1126 side channels across 32 reaches of the river system. Our results indicated that the relative explanatory contributions of physical metrics varied by response variable, providing varying evidence in support of our hypotheses, and indicating that different forms of heterogeneity matter in different ways. Side channel-level factors were more explanatory of fish community responses in side channels of upstream reaches compared to downstream reaches and percent wet forest was the most explanatory side channel-level factor of fish community responses across all models. Our classification of side channels indicated strong spatial contrasts in the abundance and diversity of side channels across reaches. Scaling up to understand how the diversity and abundance of different types of side channels contributes to landscape-scale ecological functions and processes would be useful for establishing targets for reach-scale physical heterogeneity.
... However, most river restoration projects have used the taxonomic diversity of invertebrates or fishes as indicators to assess the progress and success of the restoration projects [40][41][42][43][44][45][46][47][48][49][50] without any explicit explanation regarding how the factors relate to determining the success of the restoration projects [44,45,48]. In some cases, the habitat changes [51][52][53][54][55][56][57][58][59][60][61][62] were measured and the amenity was also evaluated [63][64][65]. ...
This study evaluated the effects of the restoration of rivers carried out by the central government on streams located in major cities in South Korea. The effects of the restoration were evaluated based on the morphological and ecological characteristics, species composition and richness of vegetation, and a Riparian Vegetation Index of the restored streams. The naturalness of the streams, based on both the morphological and ecological characteristics, as well as the Riparian Vegetation Index of the restored streams was significantly lower than that of the reference rivers. The vegetation profiles of the restored streams did not reflect the flooding regimen of the river. Furthermore, the herbaceous plants found on the streambanks give way to shrubs and then to tree-dominated vegetation, respectively. The species composition of the vegetation in the restored streams showed a significant difference from that of the reference streams and this difference was particularly more significant with regards to the herbaceous plant-dominated vegetation types. The species richness of the restored streams showed a difference among the different streams but was lower than that of the reference streams. The ratio of exotic and gardening plants occupied in the species composition of the restored streams tended to be higher than that in the reference streams. Considering the above results, the restoration effects were usually low in the restored streams. Accordingly, an active adaptive management plan was recommended to improve those problems.
... Although one-time alterations, perhaps due to river restoration (e.g., Stoffers et al., 2020) or unusually high-magnitude flows (e.g., Gendaszek et al., 2012), can generate high spatial heterogeneity, estimating turnover rate can help determine whether those shortterm gains are likely to be sustained, or whether an alternative state has been reached (Livers, Wohl, Jackson, & Sutfin, 2018;Phillips & Van Dyke, 2016). For example, comparing post-restoration to prerestoration turnover rate could indicate restoration effects on the overall erodibility of the valley bottom. ...
Spatial and temporal heterogeneity, or messiness, is a broadly desirable characteristic of river corridors and an indicator of many of the geomorphic processes that sustain fluvial ecosystems. However, quantifying geomorphic heterogeneity is complicated by a lack of consistent metrics, classification schemas for dividing the river corridor into the patches that form the basis for those metrics, and guidance on interpreting metrics. Drawing from both geomorphic and landscape ecology concepts, we offer ideas and guidance intended to help investigators, from researchers to restoration practitioners, more effectively and reliably use heterogeneity to describe river corridor processes and characteristics. We define geomorphic heterogeneity both spatially and temporally. Spatially, heterogeneity can be described by diversity, or the evenness and richness of geomorphic units, and spatial configuration, or the arrangement and shape of geomorphic units. Temporally, heterogeneity can be described by turnover rate, or the rate of change of geomorphic units. Interpretation of heterogeneity metrics depends integrally on the definition of the geomorphic unit schema on which metrics are based. Contextual information, such as measurements of process space (i.e., how much room a river has to move), disturbance frequency, and geomorphic trajectory, can also be key to interpreting measurements of heterogeneity. Geomorphic applications of heterogeneity require carefully defined geomorphic unit schemas that reflect processes and characteristics of interest, robust metrics of heterogeneity whose meaning is appropriate to the question at hand, and interpretation of those metrics based on the context of expected geomorphic processes and the disturbance regime.
... Although one-time alterations, perhaps due to river restoration (e.g., Stoffers et al., 2020) or unusually highmagnitude flows (e.g., Gendaszek et al., 2012), can generate high spatial heterogeneity, estimating turnover rate can help determine whether those short-term gains are likely to be sustained, or whether an alternative state has been reached (Livers et al., 2018;Phillips & Van Dyke, 2016). For example, comparing postrestoration to pre-restoration turnover rate could indicate restoration effects on the overall erodibility of the valley bottom. ...
Spatial and temporal heterogeneity, or messiness, is a broadly desirable characteristic of river corridors and an indicator of many of the geomorphic processes that sustain fluvial ecosystems. However, quantifying geomorphic heterogeneity is complicated by a lack of consistent metrics, classification schemas for dividing the river corridor into the patches that form the basis for those metrics, and guidance on interpreting metrics. Drawing from both geomorphic and landscape ecology concepts, we offer ideas and guidance intended to help investigators, from researchers to restoration practitioners, more effectively and reliably use heterogeneity to describe river corridor processes and characteristics. We define geomorphic heterogeneity both spatially and temporally. Spatially, heterogeneity can be described by diversity, or the evenness and richness of geomorphic units, and spatial configuration, or the arrangement and shape of geomorphic units. Temporally, heterogeneity can be described by turnover rate, or the rate of change of geomorphic units. Interpretation of heterogeneity metrics depends integrally on the definition of the geomorphic unit schema on which metrics are based. Contextual information, such as measurements of process space (i.e., how much room a river has to move), disturbance frequency, and geomorphic trajectory, can also be key to interpreting measurements of heterogeneity. Geomorphic applications of heterogeneity require carefully defined geomorphic unit schemas that reflect processes and characteristics of interest, robust metrics of heterogeneity whose meaning is appropriate to the question at hand, and interpretation of those metrics based on the context of expected geomorphic processes and the disturbance regime.
... Most river fishes rely on a sequence of inter-connected functional habitat types to complete their life history (Van Looy et al., 2019;Stoffers et al., 2022). Anadromous and catadromous fishes that have spawning migrations between seas and (upstream) rivers are particularly sensitive to the presence of longitudinal barriers (Parrish et al., 1998;Winemiller et al., 2016), whereas many sensitive rheophilic (flow-preferring) fish species are bound to the lateral connectivity of lowland rivers with their floodplains and wetlands, which they use as spawning and/or nursery habitat (Birnie-Gauvin et al., 2017;Stoffers et al., 2021). The protection and restoration of such critical (nursery) habitats is therefore essential for the recovery of river fish communities, and can be achieved through barrier removal and reconnection to wetlands and floodplains (Tickner et al., 2020). ...
... Fish species were classified in these ecological groups according to Aarts et al. (2004) and van Treeck et al. (2020). For the critical rheophilics group we removed ide (Leuciscus idus), because this species is generally thought to be a less-critical rheophilic species in terms of habitat use in the lower river Rhine (Stoffers et al., 2021;Stoffers et al., 2022), while it accounted for almost 85 % of all rheophilic catches (Suppl. materials A6). ...
... We also studied fish responses for critical rheophilics, in which we removed ide (Leuciscus idus), as this species accounted for almost 85 % of all rheophilic catches (Suppl. materials A6), and is less critical than the other 14 rheophilic species (Stoffers et al., 2021;Stoffers et al., 2022). It would seem that removing just one species would have little effect on species richness indices. ...
With a sixth mass extinction looming and freshwater biodiversity declining at unprecedented rates, evaluating ecological efficacy of river restoration efforts is critical in combatting global biodiversity loss. Here, we present a comprehensive study of the functioning for fishes of 46 river restoration projects in the river Rhine, one of the world's most heavily engineered lowland rivers. Floodplains with permanent, either one- or two-sided lateral connectivity to the main channel, favour total fish abundance, and are essential as nursery areas for riverine fishes. Habitat heterogeneity had a strong positive effect on species richness but was negatively related with fish abundances. However, the effects of environmental variables varied between ecological groups and spatial scales. Surprisingly, richness of critical rheophilic fishes declined with large-scale habitat heterogeneity (~1000 m), while it increased at small scales (~100 m), possibly because of the presence of unfavourable habitats for this ecological group at larger scales. Clearly, there is no one-size-fits-all design for river restoration projects. Whether a river section is free-flowing or impounded dictates the scope and efficacy of restoration projects and, within a river section, multiple complementary restoration projects might be key to mitigate freshwater fish biodiversity loss. An essential element for success is that these projects should retain permanent lateral connection to the main channel.
... Although one-time alterations, perhaps due to river restoration (e.g., Stoffers et al., 2020) or unusually high-magnitude flows (e.g., Gendaszek et al., 2012), can generate high spatial heterogeneity, estimating turnover rate can help determine whether those shortterm gains are likely to be sustained, or whether an alternative state has been reached (Livers, Wohl, Jackson, & Sutfin, 2018;Phillips & Van Dyke, 2016). For example, comparing post-restoration to prerestoration turnover rate could indicate restoration effects on the overall erodibility of the valley bottom. ...
Heterogeneity, or messiness, is a broadly desirable characteristic of river corridors and an indicator of many of the geomorphic processes that sustain fluvial ecosystems. However, quantifying geomorphic heterogeneity is complicated by a lack of consistent metrics, methods of dividing up the river corridor into the patches that form the basis for those metrics, and guidance on interpreting metrics. Drawing from both geomorphic and landscape ecology concepts, we offer ideas and guidance intended to help investigators, from researchers to restoration practitioners, more effectively and reliably use heterogeneity to describe river corridor processes and characteristics. We define geomorphic heterogeneity as having both a spatial and temporal dimension. Spatially, heterogeneity can be described by diversity, or the evenness and richness of geomorphic units, and spatial configuration, or the arrangement of geomorphic units relative to one another. Temporally, heterogeneity can be described by turnover rate, or the rate of change of geomorphic units. Interpretation of heterogeneity metrics depends integrally on the definition of the geomorphic unit schema on which metrics are based. Contextual information, such as measurements of process space, disturbance frequency, and geomorphic trajectory, can also be key to using effective measurements of heterogeneity. Geomorphic applications of heterogeneity require carefully defined geomorphic unit schemas that reflect processes and characteristics of interest, robust metrics of heterogeneity whose meaning is appropriate to the question at hand, and interpretation of those metrics based on the context of expected geomorphic processes and the frequency of disturbance.
... Additionally, scientific interest in the effect of river-floodplain connectivity on fish responses has increased within the 21st century. This is possibly related to the increased focus on evaluating floodplain restoration projects in recent years (Table 3) Pander Schlosser, 1991;Stoffers et al., 2021;Ward et al., 1999;Wolter et al., 2016). Furthermore, the speleophilic spawning habit of bullhead may have resulted in the general lack of information on nursery habitat requirements for this species, as this habitat is more difficult to sample compared to that of other rheophilics in this study (Balon, 1975 (d) bank slope ranging from 0° to 45°. ...
... Species abbreviations are comprised of the first two letters of genus and species names, except for Brba: Barbatula barbatula. Fish drawings were adapted from Pinder (2001) Pont & Nicolas, 2001;Schlosser, 1991;Van Looy et al., 2019;Ward et al., 1999;Winemiller et al., 2010) and are increasingly recognized as part of a well-functioning nursery area (Meulenbroek, Drexler, et al., 2018;Stoffers et al., 2021;Figure 4). When both local fish biodiversity and habitat heterogeneity are high, and habitat patches are inter-connected, river fish populations may exhibit high levels of resilience against flood pulses, global warming and other environmental changes (Elmqvist et al., 2003;Meulenbroek, Drexler, et al., 2018;Van Looy et al., 2019). ...
The large-scale degradation of riparian ecotones and of the connectivity between rivers and their floodplains has resulted in a drastic decline of rheophilic fish populations in European temperate lowland rivers. Recent river restoration projects have had variable success in effectively restoring these fish populations. Knowledge on nursery habitat requirements is considered essential for effective population restoration. However, a detailed understanding of the role of habitat heterogeneity in young-of-the-year (YOY) fish population development is limited. Therefore, we carried out a synthesis of the available knowledge on nursery habitat requirements of rheophilic fish species found in European temperate lowland rivers (<200 m elevation). From a total of 603 papers, 77 studies with primary information were selected, containing 390 associations between habitat features and YOY fish. As expected, most studies focused on static components of physical riparian habitat. Generally, YOY fish require habitats of shallow depth (<0.5 m), with slow-flowing water (<0.2 m/s), gentle bank slope (<20°), variety in substratum types (fine sand to gravel), relatively warm water and high food availability. Surprisingly, no clear ontogenetic habitat shifts between larvae and juveniles were found, which may be explained by the limited spatial-temporal resolution of most studies. Since 2011, studies on habitat heterogeneity have increased, but few have explicitly assessed its role in relation to movement patterns of YOY fish for nursery success. Therefore, we recommend that future research focuses on fish movement patterns between habitat patches in heterogeneous (river-floodplain) environments, to increase the knowledge base for effective recovery of rheophilic fish populations.
