Search

This study utilized established field and laboratory methods and multivariate statistical tools to evaluate the nutrient and potentially toxic elements (PTEs) distribution, identify possible sources, and determine potential co-existence in the Awash River. The levels of soluble reactive phosphorus (SRP), total phosphorus (TP), NO 3 -N, Mn, Ni, Cr, and Cu generally increased downstream in the upper Awash, with the highest respective values of 0.70, 1.34, 1.19, 1.58, 1.03, 0.85, and 0.11 mg L−1 at the inlet to Lake Koka. Sites found downstream of the inflow of Lake Beseka and Metehara town showed the highest levels of Fe, B, Zn, and dissolved silica. Principal components and correlation analysis findings revealed strong associations (r ≥ 0.80, p < 0.05) between nutrient parameters (SRP, TP, and NO 3 -N) and PTEs (Cu, Ni, Mn, and Cr), implying common origins and potential co-occurrences. The potential co-occurrences of these parameters may strengthen their potential individual impacts due to complex interactions. • The study evaluated nutrients and PTEs distribution, sources, and co-occurrences. • Nutrients and PTEs generally rise downstream in the upper Awash. • Urban and agriculture impacted sites showed elevated levels of nutrients and PTEs. • Fe, Pb, Ni, Mn, B, and Cr levels exceeded WHO drinking water safe limits. • Potential co-occurrence of SRP, TP, NO 3 -N, Mn, Ni, Cr, and Cu was observed. [ABSTRACT FROM AUTHOR]

• Composition of abundant and rare taxa in surface water from highly urbanization region. • Complex interactions between abundant and rare taxa in urban areas. • Deterministic processes shaping the rare taxa. • Stochastic processes primarily shape the abundant taxa. • Land use affects rare taxa, not abundant taxa. In the context of anthropogenic impacts on riverine ecosystems globally, understanding the response of bacterioplankton to anthropogenic stress is important for human and environmental health. Bacterioplankton communities are critical for maintaining ecosystem stability, but little is known about their co-occurrence networks and assembly processes in intense human-impacted plains river networks. By applying cooccurrence networks, variance partitioning, and null model analysis, we investigated the mechanisms of interaction and assembly of abundant (>1% relative abundance) and rare (<0.01%) taxa at 32 sites in river networks along an urbanization gradient (urban, suburban, and agricultural areas). Our results show that interactions between the bacterioplankton communities were more complex in urban areas than in other areas, and that environmental factors (primarily fluoride, nitrate nitrogen, and dissolved organic carbon) as well as spatial factors (i.e., Moran's Eigenvector Maps) explained most of the variation in bacterioplankton communities. Abundant taxa showed stronger spatial turnover than rare taxa, indicating that spatial factors played a greater role in the assemblage of abundant taxa. Land use types, especially impervious surfaces, had a unique influence on rare taxa, but contributed less to community change than other factors. In addition, rare taxa were mainly influenced by deterministic processes, whereas abundant taxa were more influenced by stochastic processes, especially in agricultural areas. These findings suggest that the shares of abundant and rare taxa mediate disturbances in local environmental conditions in anthropogenic river network areas, while deterministic processes play a greater role in shaping bacterioplankton communities. Overall, our study provides important insights for environmental monitoring and management in areas of intense human activity, emphasizing the need to consider both abundant and rare taxa when assessing the impact of human activities on riverine ecosystems. [ABSTRACT FROM AUTHOR]

Effective management of water quality in large rivers requires information on the influence of activities within the catchment (urban and rural) throughout the whole river basin. However, traditional water quality monitoring programmes undertaken by individual agencies normally relate to specific objectives, such as meeting quality criteria for wastewater discharges, and fail to provide information on basin-scale impacts, especially in transboundary river basins. Ideally, monitoring in large international river basins should be harmonised to provide a basin-scale assessment of sources and impacts of human activities, and the effectiveness of management actions. This paper examines current water quality issues in the Danube River Basin and evaluates the approach to water quality monitoring in the context of providing information for a basin-wide management plan. Lessons learned from the monitoring programme in the Danube are used to suggest alternative approaches that could result in more efficient generation of water quality data and provide new insights into causes and impacts of variations in water quality in other large international river basins. [ABSTRACT FROM AUTHOR]

• Lateral hydrological connectivity significantly shapes fish community traits in floodplains. • Isolated habitats lead to trait convergence, connected areas promote trait divergence. • Intermediate connectivity maintains highest temporal variability in fish communities. • Maintaining diverse connectivity levels is crucial for floodplain conservation. • Considering multiple trait attributes better reveals fish community responses. Connectivity, a fundamental concept in ecology, refers to the extent to which different habitats or ecosystems are interconnected through the movement of organisms, nutrients, and energy. Lateral hydrological connectivity (LHC) plays an especially critical role in shaping aquatic community organization in river-floodplain systems. However, a comprehensive understanding of various trait responses to LHC remains elusive. We characterized how attributes of fish community traits, specifically composition, divergence, and temporal variability respond to LHC in the Austrian-Hungarian floodplains of the Danube River using environmental DNA (eDNA) metabarcoding. Trait composition was quantified by community-level weighted means (CWM) as the degree of changes in trait responses along the LHC gradient from isolated oxbows to the main river. Divergence was measured using Rao's quadratic functional diversity index and a null model approach to calculate standardized effect sizes (SES), with larger SES values indicating greater divergence and smaller values indicating convergence. Temporal variability, representing the degree of instability in community traits over time, was calculated using a functional beta diversity measure for multiple communities. Our findings revealed apparent compositional changes for many trait variables, highlighting the significance of LHC in shaping community functional diversity. Divergence patterns indicated that isolated habitats foster trait convergence presumably due to habitat filtering, whereas more connected areas promote trait divergence due to higher species richness and habitat availability. Temporal variability of traits associated with flow preference exhibited a hump-shaped relationship with LHC, suggesting intermediate connectivity zones are hotspots of ecological dynamism. The study suggests that examining composition, divergence, and temporal variability together provides a more complete understanding of trait responses to connectivity, stressing the importance of maintaining diverse connectivity levels in river-floodplain systems for effective conservation and ecosystem management. [ABSTRACT FROM AUTHOR]

[Display omitted] • Loss of longitudinal connectivity on average at 72 % in the Austrian Danube system. • Barrier passability increased by fish passes between 20 % and 24 %. • Natural connectivity gradient strongly disrupted. • Measures to connect and restore habitats of potamodromous fish populations needed. In this study, we explored how barriers such as dams have affected the longitudinal connectivity of riverine habitats from the perspective of potamodromous fish. For this purpose, connectivity changes are investigated in the central part of the Austrian Danube system, where the national reporting for the EU Water Framework Directive provides detailed information on the position and characteristics of barriers as well as the distribution range of native fish species. This assessment is based on an estimation regarding the quantitative upstream and downstream passability of individual barriers, where we further investigate three different passability scenarios to account for uncertainties. We then apply several combinations of passability scenarios and assumptions on dispersal distances to calculate a series of network-based reach and catchment connectivity indices. On average, the estimation of barrier passability indicated a high downstream passability, while upstream passability was substantially lower across scenarios. Furthermore, existing fish passes were estimated to have increased passability on average between 20 % and 24 %. Overall, the results indicated a strong effect of barriers on the longitudinal connectivity of the investigated river network. Catchment scale indices revealed a loss of connectivity, which increased with dispersal distance. Reach connectivity indices displayed a strong disruption of the natural connectivity gradient along the river network and indicated that individual river reaches have, on average, become more isolated in addition to the overall decrease in connectivity. The average loss of connectivity across scenarios was estimated at 72 % (SD = 16 %) when taking into account all connections to other reaches and 66 % (SD = 7 %) when only connections to upstream reaches were considered. We conclude that longitudinal connectivity in the Austrian Danube system is still severely compromised, making it increasingly challenging for potamodromous fish species to complete their life cycle. This issue is further amplified by the severe loss of fish habitats as a consequence of river engineering. [ABSTRACT FROM AUTHOR]

• Connectivity is a key property of river-floodplain systems. • We use graph theory describing main transport pathways. • PLS regression is used to model and predict floodplain functions. • The approach shows main deficits due to anthropogenic alteration. • We propose type-specific restoration options. Connectivity is a crucial property of the river-floodplain ecosystem. Reduction of connectivity, fragmentation and isolation effects, impacting ecological functions and biodiversity, is one of the most critical threats to floodplain systems. We use a graph theoretical approach for analyzing possible transport pathways in the system (directed, undirected, overland, seepage) and relate them to ecosystem functions in a river-floodplain system impacted by engineering structures (Danube River, Vienna, Austria). We studied essential ecological functions using indicators on sediment composition and quality, hydrochemical conditions, and macrophyte coverage. Our results indicate that sediment transport and composition are widely driven by directional flow and connectivity. In contrast, the exchange of water and nutrients is dominated by seepage exchange in the system. Macrophytes are dominating in water bodies which are not relevant for directed transport. The graph theoretical approach solely based on remotely sensed data can be used to classify floodplain water bodies related to their essential function and importance in the network and identify main deficits and potential restoration measures. It can, therefore, be an essential tool for prioritizing systems for management measures and restoration actions. [ABSTRACT FROM AUTHOR]

Floodplains are highly diverse landscape elements within river systems and among the most endangered ecosystems worldwide. In this paper we complement indices developed to assess the ecological status of floodplain systems, compliant with the EU Water Framework Directive, to an overall “Benthic Invertebrate Floodplain Index” (BIFI). With the addition of taxa (mainly oligochaetes, chironomidae and amphipoda) to the floodplain index (FI), caddisfly (CHI), and dragon fly (OHI) indices a new extended BIFI can be calculated. We provide values for the calculation of the index derived from a comprehensive dataset of Austrian floodplain waters complemented by literature data. Values are given for those taxonomic groups which are abundant in the Austrian Danube and determinable in reasonable time. The new index was compared to published floodplain indices and tested with an independent data set at two floodplain segments along the Austrian Danube. The newly classified benthic invertebrates (NCBI) showed a good performance in comparison to the so far published indices and extend these to a better coverage of dynamic water bodies. Further the inclusion of abundant and species rich taxa improves the robustness of calculated values already with a low sampling effort. Altogether it is a promising tool for the integrated assessment of the ecological status of river-floodplain systems according to the EU Water Framework Directive. [ABSTRACT FROM AUTHOR]

Fragmentation affects river ecosystems worldwide by dampening the movement and dispersal of aquatic organisms and material (such as sediment, water, nutrients) across the river network. In this paper, we develop river connectivity indices to explain biodiversity patterns, prioritize reaches that need habitat restoration and barriers that need improvement. We provide a general framework for calculating connectivity indices by disentangling the contribution of the river network's physical setup (structural connectivity) from the process-driven and biota-related contribution (functional connectivity). To facilitate the calculations, the R package 'riverconn' is introduced. A prioritization of habitats and barriers is carried out for the Ebro river (North-West Iberian Peninsula) using indices setups accounting for different classes of organisms and dispersal traits. Resulting prioritizations are very diverse. 'Riverconn' can support scientists and managers working on riverscape planning and population and community ecology by providing a means to compute and compare a wide array of fragmentation indices. • The R package 'riverconn' is introduced to calculate catchment and reach connectivity indices. • Structural and functional connectivity are disentangled. • Based on the formulation, connectivity indices and resulting habitats and barriers prioritization can be highly diverse. • 'riverconn' can be used in planning conservation and connectivity improvement, population and community ecology. [ABSTRACT FROM AUTHOR]

Abstract: The hydrological exchange conditions strongly determine the biogeochemical dynamics in river systems. More specifically, the connectivity of surface waters between main channels and floodplains is directly controlling the delivery of organic matter and nutrients into the floodplains, where biogeochemical processes recycle them with high rates of activity. Hence, an in-depth understanding of the connectivity patterns between main channel and floodplains is important for the modelling of potential gas emissions in floodplain landscapes. A modelling framework that combines steady-state hydrodynamic simulations with long-term discharge hydrographs was developed to calculate water depths as well as statistical probabilities and event durations for every node of a computation mesh being connected to the main river. The modelling framework was applied to two study sites in the floodplains of the Austrian Danube River, East of Vienna. Validation of modelled flood events showed good agreement with gauge readings. Together with measured sediment properties, results of the validated connectivity model were used as basis for a predictive model yielding patterns of potential microbial respiration based on the best fit between characteristics of a number of sampling sites and the corresponding modelled parameters. Hot spots of potential microbial respiration were found in areas of lower connectivity if connected during higher discharges and areas of high water depths. [Copyright &y& Elsevier]

Abstract: River/floodplain restoration programs are often based on type-specific reference conditions of the respective river section. Most large rivers in the industrialized world are heavily degraded and lack near-natural reference sites. For that reason, historical analyses of the pre-channelization state have been used to define adequate restoration targets at the Austrian Danube section in the Alluvial Zone National Park downstream from Vienna. This study compares new reference data derived from 3D-reconstructions in the form of digital terrain models from two historical Danube river landscapes: the Machland floodplain in 1812 and the former floodplain in Vienna in 1849. The focus is on the original hydrological surface and subsurface connectivity of the river-floodplain systems related to different flow situations. Here, we use water cover, shorelines, depth of the groundwater table and inundation depth as surrogates for measuring connectivity. The results show that the two study sites naturally constituted extreme formations of the Austrian anabranching Danube sections. The Machland section was one of the narrowest floodplains but highly dynamic, and the Vienna/Lobau section was one of the broadest, whereby only the central part close to the main channel originally showed high morphological turnover. The analyses of hydrological surface connectivity relative to total floodplain extension reveal significant differences due to their basic geological and geographical conditions. Despite these basic differences, both study sites – in absolute numbers – showed similar extensions of the water bodies at low and mean flow. The depths of the groundwater table related to mean flow were also comparable. Prior to channelization, the groundwater conditions in both floodplains favored the formation of wet to moist alluvial forest communities. Up until today, the two river landscapes continue to undergo different developments: both river sections are impounded, but the Machland floodplain still represents a rural site while the Vienna site has been utilized more intensively as building land and for urban infrastructure. As a consequence of the diverse human interventions in the 19th and 20th century, river bed degradation and aggradation of sediments in the floodplains have significantly truncated fluvial dynamics and hydrological connectivity. In addition, these phenomena have substantially deepened the groundwater table in both study sites. The results contribute to the identification of river/floodplain-type-specific reference conditions and provide an additional decision basis for discussing appropriate management strategies in the degraded riverine ecosystems. [Copyright &y& Elsevier]