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This article, published in the journal Inland Waters, discusses the relationship between chlorophyll a concentration and macrophyte richness in lakes. The study found that macrophyte richness decreases gradually as chlorophyll a concentration increases. Meadow-forming Characeae declined at lower chlorophyll a concentrations compared to canopy-forming species. The study provides estimates of critical concentrations for both growth forms and suggests that this information can be used in lake management and restoration efforts. The document is a compilation of scientific articles on the role of roots in the nutrition of aquatic vascular plants, covering topics such as macrophytic vegetation distribution, phosphorus uptake, restoration measures, and nutrient-macrophyte relationships. These articles provide valuable insights for researchers studying aquatic plants. [Extracted from the article]

Woody riparian vegetation (WRV) benefits benthic macroinvertebrates in running waters. However, while some functions are provided by WRV irrespective of surrounding and catchment land use, others are context‐specific. In recent large‐scale studies, effects of WRV on macroinvertebrates were therefore small compared to catchment land use, raising the question about the relevance of WRV for restoration.Model‐based recursive partitioning was used to identify context‐dependent effects of WRV on the macroinvertebrates' ecological status in small (catchment area 10–100 km2) lowland (n = 361) and mountain (n = 748) streams. WRV cover was quantified from orthophotos along the near (500 m) and far (5000 m) upstream river network and used to predict the site's ecological status. Agricultural, urban and woodland cover at the local and catchment scales along with hydromorphology were considered as partitioning variables.In rural agricultural landscapes, the effect of WRV on the ecological status was large, indicating that establishing near‐upstream WRV can improve the ecological status by as much as two of the five classes according to the EU Water Framework Directive.Even in urban landscapes, effects of far‐upstream WRV were large if catchments had a moderate share of agricultural land use in addition. The beneficial effects of WRV were only limited in purely urban catchments or in a multiple stressor context.Synthesis and applications. While woody riparian vegetation (WRV) can even improve the ecological status in urban settings, it is especially relevant for river management in rural agricultural catchments, where developing WRV potentially are effective measures to achieve good ecological status. [ABSTRACT FROM AUTHOR]

Woody riparian buffers (hereafter, 'woody buffers') are frequently considered as important to mitigate the effects of stressors on streams and rivers. While several individual studies addressing nutrients, pesticides, water temperature and different biotic components support this conjecture, no study has addressed the effects of woody buffers on riverine biota at country‐wide scales.We used a comprehensive dataset from sampling sites on 1082 catchments in France, comprising samples of benthic invertebrates, along with data on river size, physico‐chemistry, hydromorphology, riparian and catchment land use and woody buffers at sampling sites and upstream.Using partial least square modelling, we delineated the effects of the different environmental variables on two benthic invertebrate metrics, separately for siliceous and calcareous rivers.Overall, models explained 49% (calcareous) and 39% (siliceous) of the variation in benthic invertebrate metrics. Direct effects of woody buffers on benthic invertebrate metrics were marginal, while physico‐chemical conditions and catchment land use explained most of the deviance. Direct and indirect effects of woody buffer together covered up to 6% (upstream scale) plus 2% (local scale) of the explained variability.Synthesis and applications. In this national‐scale study, on 1082 catchments, we investigated the potential of woody buffers to mitigate the effects of catchment‐scale and local‐scale stressors on macroinvertebrate biodiversity. Our results underline that the establishment of woody buffers is not necessarily a sufficient measure to solve the problem of deteriorating riverine macroinvertebrate communities, especially in catchments prone to intense land use. Nevertheless, two main outcomes included that local woody patches are not sufficient and that woody buffers should be established along longer river stretches. Also, accompanying catchment‐scale measures should be promoted to reduce the effects of intense land use and pollution to a level that enables woody buffers to be effective as well. [ABSTRACT FROM AUTHOR]

Sixteen ecosystem services were quantified for the riverine landscapes of the Nahe, Stever (Germany), Bresse plain, and Azergues (France), to assess the effects of riparian woodland cover. Future woodland cover in 2050 was modeled to reflect contrasting scenarios of river management aligned to the well‐established shared socioeconomic pathways. The scenarios are labeled as current, pessimistic, best practice, and ambitious riparian management practices (RMPs). We linked services to floodplain land use and river morphology and quantified them separately for spatial segments (0.5–1 km in length, n = 118–3419, depending on river length), using an analytical framework, the "Mononen cascade." Conservative monetary value estimates were based on net producer income before tax and subsidy, a shadow market price for carbon, flood damage functions, or willingness to pay for recreation and non‐use. Most services were linked to land use, some affected the value of other services through simple rules (woodland shade affected trout survival hence angling benefit, a minimum of woodland affected pest regulation, hence crop productivity). In the current landscape state, provisioning, regulating, and cultural services all showed optimum curves with woodland cover: Provisioning services and cultural services were maximal around 45%, whereas this was around 30% for regulating services. More woodland was present in steeper near‐source segments. Averaged across rivers, mean total service provision was estimated at 1084 ± 4 €·ha−1·yr−1, with 40%, 36%, and 24% contributed by, respectively, provisioning, regulating, and cultural services. The three scenarios led to a limited change in total ecosystem service delivery, even if mean woodland cover was reduced from 27% to 17% in the pessimistic RMP and increased to 70% in the ambitious RMP for the most extreme case of the Stever. Provisioning services declined with increased woodland cover and cultural services increased. Regulating services did not change that much, because they are dominated by flood prevention in our assessment. The "best practice" scenario appeared to combine a modest increase in cultural services with a slight increase in provisioning service. An ambitious nature conservation objective as in the ambitious RMP appears possible without seriously compromising overall societal benefit. [ABSTRACT FROM AUTHOR]

Water temperature is a key driver for riverine biota and strongly depends on shading by woody riparian vegetation in summer. While the general effects of shading on daily maximum water temperature Tmax are well understood, knowledge gaps on the role of the spatial configuration still exist. In this study, the effect of riparian buffer length, width, and canopy cover (percentage of buffer area covered by woody vegetation) on Tmax was investigated during summer baseflow using data measured in seven small lowland streams in western Germany (wetted width 0.8–3.7 m). The effect of buffer length on Tmax differed between downstream cooling and heating: Tmax approached cooler equilibrium conditions after a distance of 0.4 km (~45 min travel‐time) downstream of a sharp increase in canopy cover. In contrast, Tmax continued to rise downstream of a sharp decrease in canopy cover along the whole 1.6 km stream length investigated. The effect of woody vegetation on Tmax depended on buffer width, with changes in canopy cover in a 10 m wide buffer being a better predictor for changes in Tmax compared to a 30 m buffer. The effect of woody vegetation on Tmax was linearly related to canopy cover but also depended on daily temperature range Trange, which itself was governed by cloudiness, upstream canopy cover, and season. The derived empirical relationship indicated that Tmax was reduced by −4.6°C and increased by +2.7°C downstream of a change from unshaded to fully shaded conditions and vice versa. This maximum effect was predicted for a 10 m wide buffer at sunny days in early summer, in streams with large diel fluctuations (large Trange). Therefore, even narrow woody riparian buffers may substantially reduce the increase in Tmax due to climate change, especially in small shallow headwater streams with low baseflow discharge and large daily temperature fluctuations. [ABSTRACT FROM AUTHOR]

Global change has the potential to affect river flow conditions which are fundamental determinants of physical habitats. Predictions of the effects of flow alterations on aquatic biota have mostly been assessed based on species ecological traits (e.g., current preferences), which are difficult to link to quantitative discharge data. Alternatively, we used empirically derived predictive relationships for species' response to flow to assess the effect of flow alterations due to climate change in two contrasting central European river catchments. Predictive relationships were set up for 294 individual species based on (1) abundance data from 223 sampling sites in the Kinzig lower-mountainous catchment and 67 sites in the Treene lowland catchment, and (2) flow conditions at these sites described by five flow metrics quantifying the duration, frequency, magnitude, timing and rate of flow events using present-day gauging data. Species' abundances were predicted for three periods: (1) baseline (1998-2017), (2) horizon 2050 (2046-2065) and (3) horizon 2090 (2080-2099) based on these empirical relationships and using high-resolution modeled discharge data for the present and future climate conditions. We compared the differences in predicted abundances among periods for individual species at each site, where the percent change served as a proxy to assess the potential species responses to flow alterations. Climate change was predicted to most strongly affect the low-flow conditions, leading to decreased abundances of species up to -42%. Finally combining the response of all species over all metrics indicated increasing overall species assemblage responses in 98% of the studied river reaches in both projected horizons and were significantly larger in the lower-mountainous Kinzig compared to the lowland Treene catchment. Such quantitative analyses of freshwater taxa responses to flow alterations provide valuable tools for predicting potential climate-change impacts on species abundances and can be applied to any stressor, species, or region. [ABSTRACT FROM AUTHOR]

Habitat suitability and the distinct mobility of species depict fundamental keys for explaining and understanding the distribution of river fishes. In recent years, comprehensive data on river hydromorphology has been mapped at spatial scales down to 100 m, potentially serving high resolution species-habitat models, e.g., for fish. However, the relative importance of specific hydromorphological and in-stream habitat variables and their spatial scales of influence is poorly understood. Applying boosted regression trees, we developed species-habitat models for 13 fish species in a sand-bed lowland river based on river morphological and in-stream habitat data. First, we calculated mean values for the predictor variables in five distance classes (from the sampling site up to 4000 m up- and downstream) to identify the spatial scale that best predicts the presence of fish species. Second, we compared the suitability of measured variables and assessment scores related to natural reference conditions. Third, we identified variables which best explained the presence of fish species. The mean model quality (AUC = 0.78, area under the receiver operating characteristic curve) significantly increased when information on the habitat conditions up- and downstream of a sampling site (maximum AUC at 2500 m distance class, +0.049) and topological variables (e.g., stream order) were included (AUC = +0.014). Both measured and assessed variables were similarly well suited to predict species’ presence. Stream order variables and measured cross section features (e.g., width, depth, velocity) were best-suited predictors. In addition, measured channel-bed characteristics (e.g., substrate types) and assessed longitudinal channel features (e.g., naturalness of river planform) were also good predictors. These findings demonstrate (i) the applicability of high resolution river morphological and instream-habitat data (measured and assessed variables) to predict fish presence, (ii) the importance of considering habitat at spatial scales larger than the sampling site, and (iii) that the importance of (river morphological) habitat characteristics differs depending on the spatial scale. [ABSTRACT FROM AUTHOR]

River biota are affected by global reach-scale pressures, but most approaches for predicting biota of rivers focus on river reach or segment scale processes and habitats. Moreover, these approaches do not consider long-term morphological changes that affect habitat conditions. In this study, a modelling framework was further developed and tested to assess the effect of pressures at different spatial scales on reach-scale habitat conditions and biota. Ecohydrological and 1D hydrodynamic models were used to predict discharge and water quality at the catchment scale and the resulting water level at the downstream end of a study reach. Long-term reach morphology was modelled using empirical regime equations, meander migration and 2D morphodynamic models. The respective flow and substrate conditions in the study reach were predicted using a 2D hydrodynamic model, and the suitability of these habitats was assessed with novel habitat models. In addition, dispersal models for fish and macroinvertebrates were developed to assess the re-colonization potential and to finally compare habitat suitability and the availability / ability of species to colonize these habitats. Applicability was tested and model performance was assessed by comparing observed and predicted conditions in the lowland Treene River in northern Germany. Technically, it was possible to link the different models, but future applications would benefit from the development of open source software for all modelling steps to enable fully automated model runs. Future research needs concern the physical modelling of long-term morphodynamics, feedback of biota (e.g., macrophytes) on abiotic habitat conditions, species interactions, and empirical data on the hydraulic habitat suitability and dispersal abilities of macroinvertebrates. The modelling framework is flexible and allows for including additional models and investigating different research and management questions, e.g., in climate impact research as well as river restoration and management. [ABSTRACT FROM AUTHOR]

In addition to ecological factors, evolutionary processes can determine the invasion success of a species. In particular, genetic admixture has the potential to induce rapid evolutionary change, which can result from natural or humanassisted secondary contact between differentiated populations. We studied the recent range expansion of zander in Germany focusing on the interplay between invasion and genetic admixture. Historically, the rivers Elbe and Danube harboured the most north-western source populations from which a north-westward range expansion occurred. This was initiated by introducing zander outside its native range into rivers and lakes, and was fostered by migration through artificial canals and stocking from various sources. We analysed zander populations of the native and invaded ranges using nuclear and mitochondrial genetic markers. Three genetic lineages were identified, which were traced to ancestral ranges. Increased genetic diversity and admixture in the invaded region highlighted asymmetric gene flow towards this area. We suppose that the adaptive potential of the invading populations was promoted by genetic admixture, whereas competitive exclusion in the native areas provided a buffer against introgression by novel genotypes. These explanations would be in line with evidence that hybridization can drive evolutionary change under conditions when new niches can be exploited. [ABSTRACT FROM AUTHOR]

It is commonly assumed that the colonization of restored river reaches by fish depends on the regional species pools; however, quantifications of the relationship between the composition of the regional species pool and restoration outcome are lacking. We analyzed data from 18 German river restoration projects and adjacent river reaches constituting the regional species pools of the restored reaches. We found that the ability of statistical models to describe the fish assemblages established in the restored reaches was greater when these models were based on ‘biotic’ variables relating to the regional species pool and the ecological traits of species rather than on ‘abiotic’ variables relating to the hydromorphological habitat structure of the restored habitats and descriptors of the restoration projects. For species presence in restored reaches, ‘biotic’ variables explained 34% of variability, with the occurrence rate of a species in the regional species pool being the most important variable, while ’abiotic’ variables explained only the negligible amount of 2% of variability. For fish density in restored reaches, about twice the amount of variability was explained by ‘biotic’ (38%) compared to ‘abiotic’ (21%) variables, with species density in the regional species pool being most important. These results indicate that the colonization of restored river reaches by fish is largely determined by the assemblages in the surrounding species pool. Knowledge of species presence and abundance in the regional species pool can be used to estimate the likelihood of fish species becoming established in restored reaches. [ABSTRACT FROM AUTHOR]

1. Using an extensive data set from 18 river restoration projects in the lower mountain ranges of Germany and 5462 river reaches in their surroundings, we estimated the spatial extent of the regional fish species pool from which restored river reaches are colonised. 2. Restoration resulted in a marginally significant increase in fish species richness; however, restored reaches still deviated markedly from natural reference conditions. Nearly all (96.6%) species occurring in restored reaches were present in reaches within a distance of 5 km up- or downstream of the restored reach. 3. Species richness in restored reaches was correlated with species richness within a 5-km species pool. This relationship was more pronounced for common than for rare fishes and applied to both the total number of fish species at the restored reach and the number of additional fish species that were not present at unrestored conditions. 4. The richness of the regional species pools was greatly impoverished. On average, only 50% of all species considered to represent natural reference assemblages were present. The limited success in establishing natural fish assemblages in restored reaches was attributed to spatial limitation (e.g. due to fragmentation) and an impoverished regional species pools from which restored reaches recruit. 5. We recommend that integrated river restoration management should consider not only the abiotic prerequisites of successful restorations, but also the structure and quality of the regional species pool. [ABSTRACT FROM AUTHOR]

1. Wood is increasingly used in restoration projects to improve the hydromorphological and ecological status of streams and rivers. However, despite their growing importance, only a few of these projects are described in the open literature. To aid practitioners, we conducted a postal mail survey to summarize the experiences gained in central Europe and compile data on 50 projects. 2. Our results indicated the potential for improvement from an ecological point of view, as the number and total wood volume, and the median volume of single wood structures placed in the streams per project, were low compared with the potential natural state. Moreover, many wood structures were placed nearly parallel to the water flow, reducing their beneficial effect on stream hydraulics and morphology. 3. Restoration success has been monitored in only 58% of the projects. General conclusions drawn include the following. (i) The potential effects of wood placement must be evaluated within a watershed and reach-scale context. (ii) Wood measures are most successful if they mimic natural wood. (iii) Effects of wood structures on stream morphology are strongly dependent on conditions such as stream size and hydrology. (iv) Wood placement has positive effects on several fish species. (v) Most projects revealed a rapid improvement of the hydromorphological status. 4. Most of the wood structures have been fixed, called ‘hard engineering’. However, soft engineering methods (use of non-fixed wood structures) are known to result in more natural channel features for individual stream types, sizes and sites, and are significantly more cost-effective. 5. Synthesis and applications. Large wood has been used successfully in several projects in central Europe, predominantly to increase the general structural complexity using fixed wood structures. Our results recommend the use of less costly soft engineering techniques (non-fixed wood structures), higher amounts of wood, larger wood structures and improved monitoring programmes for future restoration projects comparable with those in this study. We recommend the use of ‘passive restoration’ methods (restoring the process of wood recruitment on large scales) rather than ‘active restoration’ (placement of wood structures on a reach scale), as passive restoration avoids the risk of non-natural amounts or diversity of wood loading developing within streams. Local, active placement of wood structures must be considered as an interim measure until passive restoration methods have increased recruitment sufficiently. [ABSTRACT FROM AUTHOR]

Bayesian networks (BN) have increasingly been applied in water management but not to estimate the efficacy of riparian buffer zones (RBZ). Our methodical study aims at evaluating the first BN to predict the RBZ efficacy to retain sediment and nutrients (dissolved, total, and particulate nitrogen and phosphorus) from widely available variables (width, vegetation, slope, soil texture, flow pathway, nutrient form). To evaluate the influence of parent nodes and how the number of states affects prediction errors, we used a predefined general BN structure, collected 580 published datasets from North America and Europe, and performed classification tree analyses and multiple 10-fold cross-validations of different BNs. These errors ranged from 0.31 (two output states) to 0.66 (five states). The outcome remained unchanged without the least influential nodes (flow pathway, vegetation). Lower errors were achieved when parent nodes had more than two states. The number of efficacy states influenced most strongly the prediction error as its lowest and highest states were better predicted than intermediate states. While the derived BNs could support or replace simple design guidelines, they are limited for more detailed predictions. More representative data on vegetation or additional nodes like preferential flow will probably improve the predictive power. [ABSTRACT FROM AUTHOR]