•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.
A new R software package, RAC, is presented. RAC allows to simulate the rearing cycle of 4 species, finfish and shellfish, highly important in terms of production in the Mediterranean Sea. The ...package works both at the scale of the individual and of the farmed population. Mathematical models included in RAC were all validated in previous works, and account for growth and metabolism, based on input data characterizing the forcing functions-water temperature, and food quality/quantity. The package provides a demo dataset of forcings for each species, as well as a typical set of husbandry parameters for Mediterranean conditions. The present work illustrates RAC main features, and its current capabilities/limitations. Three test cases are presented as a proof of concept of RAC applicability, and to demonstrate its potential for integrating different open products nowadays provided by remote sensing and operational oceanography.
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•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.
The two-stage ditch is a river restoration technique that aims at improving the sediment regime and lateral channel connectivity by recreating a small floodplain alongside a stream reach. This study ...aimed to analyze the efficiency of a two-stage ditch in improving the stream sediment structure and functions under different hydrological conditions (baseflow, post-bankfull, post-flood). Stream sediments were collected in channel sections adjacent to the two-stage ditch, adjacent to a natural floodplain along channelized reaches without inundation areas. Grain sizes, organic matter content and phosphorous (P) fractions were analyzed along with functional parameters (benthic respiration rate and P adsorption capacity, EPC0). The reach at the two-stage ditch showed no changes in sediment texture and stocks, while the floodplain reach showed higher fines and organic matter content under all hydrological conditions. The sediments in degraded reaches were more likely to be P sources, while they were more in equilibrium with the water column next to the natural floodplains and the two-stage ditch. Only functional parameters allowed for assessing the restoration effects on improving the sediment stability and functionality. Due to its sensitivity, the use of P adsorption capacity is recommended in future studies aiming at evaluating the response of river sediments to restoration measures under different hydrological conditions.
It is a widely discussed topic in restoration ecology to use organic carbon (OC) management to increase nutrient uptake in chronically loaded agricultural streams. However, although nitrate uptake ...has been shown to correlated closely with the availability of dissolved OC, this relationship is less clear for phosphate. Likewise, the role of particulate OC (POC) on stimulating nutrient uptake has to be clarified. We aimed at investigating the effects of leaf additions on the net uptake of soluble reactive phosphorus and nitrate‐nitrogen from the water column by benthic biofilms in combined laboratory flume and batch experiments.
Fine sediments were colonised under nutrient‐enriched conditions in the dark (dark‐grown heterotrophic biofilms) and under a 12/12‐hr dark/light cycle (light‐grown photoautotrophic biofilms) in flumes. In each light treatment, half of the biofilms were grown under strong OC‐limitation, the other half under near‐optimal C:N:P ratios. For the uptake experiments, the colonised sediments were incubated in nutrient‐enriched water to which (1) fresh alder leaves, (2) pre‐leached leaves, or (3) no leaves were added. Net nutrient uptake (or release) rates were determined via the change in nutrient concentrations in the water column over time.
Net phosphorus uptake by dark‐grown biofilms was significantly increased by the addition of leaves. Despite their high initial nutrient leaching, fresh leaves showed stronger stimulating effects on the net P uptake than leached leaves over the entire experiment. Furthermore, biofilms grown under near‐optimum C:N:P ratios responded stronger to the POC supply than biofilms grown under C‐limited conditions. In contrast to dark‐grown biofilms, leaf additions had no significant effects on the net P uptake by light‐grown biofilms. We also found no effects of leaf additions on net nitrate uptake.
Our study shows that an increased POC supply in nutrient‐impacted streams may boost heterotrophic phosphate uptake. However, the stimulating effect of the POC addition depends on a variety of POC‐dependent (e.g. respiration, heterotrophic assimilation, denitrification) and independent (e.g. adsorption, photoautotrophic assimilation) processes, making nutrient control via POC management challenging. We suggest application of management approaches that focus on restoration of riparian areas and wetlands to increase the amount of natural, complex POC with a moderate degradability, thus keeping the heterotrophic metabolism low but potentially stimulating in‐stream N and P retention.
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.
Extreme sea levels (ESLs) affect coastal ecosystems worldwide. Protection and adaptation strategies rely on the characterization of the extreme's occurrence probability in the future. However, ...knowledge on the occurrence rate and duration of ESLs is also needed to properly characterize the associated future risk. In this paper, we focus on the Venice lagoon, where a system of storm surge barriers can disconnect the lagoon from the sea to mitigate ESLs. Using long-term (96 years) sea level records, we model occurrence rate and duration of ESLs while accounting explicitly for seasonality and mean sea level rise. While historically ESLs occurred in the winter season, we project a significant increase (up to 10-fold with a mean sea level increase of +100 cm) of the occurrence rate also in the summer season, when disconnections from the sea can have profound impacts on the lagoon's ecosystem. We also predict an increase in ESLs durations up to 200 h, leading to longer disconnections of the lagoon from the sea in the future. Therefore, several adaptation strategies will be needed to limit the adverse effects of storm surge barriers on the lagoon ecosystem.
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•Point process model for extreme sea levels duration and occurrence frequency•Forecast under climate change for the Venice Lagoon and its storm surge barrier system•Future increases in extreme sea levels duration and occurrence depend on the season.•Storm surge barriers are likely to be operated also in summer in the future.
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•Modeling cascade used to simulate natural water retention measures (NWRM).•Impact of NWRMs on fine bed material deposits predicted at different spatial scales.•Identification of ...controls for fine bed material deposits drives NWRM choice.•Effectiveness of NWRMs diagnosed at different spatial scale is diverse.•Both catchment and reach scale effects should be considered for measures planning.
Natural water retention measures (NWRMs) belong to the broad range of nature-based solutions and are receiving increased attention for targeting environmental problems of river catchments as they effectively support the restoration of natural processes and cycles. Challenges involved in NWRMs planning include the development of tools able to project and diagnose the effects at different spatial scales (e.g., catchment or the reach). This paper focuses on NWRMs addressing fine bed material deposits (FBMDs), with the aim of a) assessing factors and scales that control FBMDs; b) simulating the cascading impact of NWRMs on catchment hydrology, sediment loads, reach hydraulics, and FBMD; and c) assessing the effectiveness of NWRMs in targeting FBMDs at different spatial scales (catchment and reach). A modeling cascade was used to propagate the effects. This included a hydrological model (SWAT), a hydraulic model (HEC-RAS), and a spatially distributed Random Forest ensemble to model FBMDs risk for the Aist catchment (650 km2) Austria. Our results show that upstream sediment loads are an important predictor controlling the likelihood of sites to be classified as low risk. The effectiveness of NWRMs in reducing FBMDs is variable and depends on the target risk class. Vegetated filter strips that can trap sediments before they enter into the stream are more effective in increasing the extent of the river network towards natural conditions (5% increase compared to baseline). Sediment retention ponds are effective in reducing the extent of reaches where instream habitats are completely clogged by FBMDs (−8%). Hydromorphological improvements are effective in targeting sites where FBMDs are transported even during mean flow (−10%). A combination of NWRMs could benefit both high-risk as well as low-risk sites. The effectiveness of NWRMs can greatly differ when both reach and catchment diagnostics are analyzed. Thus, multi-scale assessment of the effectiveness can support NWRMs planning by unraveling all the potential benefits and highlighting tradeoffs hidden by analyses limited to a single spatial scale.
The identification and prioritization of sites for conservation actions to protect biodiversity in lotic systems is crucial when economic resources or available areas are limited. Challenges include ...the incorporation of multi-scale interactions, and the application of species distribution models (SDMs) to rare organism with multiple life stages. To support the planning of conservation actions for the highly endangered Freshwater Pearl Mussel Margaritifera margaritifera (FPM), this paper aims at developing an ecohydrological modeling cascade including a hydrological model (SWAT) and a hydraulic model (HEC-RAS). Building on hydrology and hydraulics, Random Forest models for potential risk to juveniles due to sand accumulation, SDMs for adults habitat niche, and a landscape connectivity assessment of dispersal potential were developed. The feasibility of such models integration was tested in the Aist catchment (630 km2) in Austria. The potential FPM habitat and the sand accumulation risk for the whole catchment were predicted with good accuracy. Results show that while the potentially suitable habitats for adults FPM cover 34% of the river network, only few habitat patches can maximize the dispersal potential (4% of the river network) and even less are showing limited impact of accumulations (3.5% of river network). No habitat patch that meets all the three criteria is available, suggesting approaches that target the patch-specific critical life stage-factors are promising for conservation.
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•Ecohydrological modeling cascades support multi-scaled conservation planning.•A tool for modeling the life stages of the Freshwater Pearl Mussels is developed.•Hydrological, hydraulic, sand accumulation, species distribution models are linked.•Sites for life-stage-specific conservation actions are identified and prioritized.•Critical life stages drive choice of conservation action.
The freshwater pearl mussel Margaritifera margaritifera is a benthic organism sensitive to hydrological regime alterations and habitat degradation driven by excessive fine bed material deposit ...(FBMD). Both issues are potentially exacerbated by climate change. Understanding how climate change affects future mussel habitats and the dispersal among them (dependent on the brown trout as fish host) can support the planning of effective conservation actions.
To project the impacts of climate change on the mussel, a semi‐mechanistic modelling cascade was implemented for the Aist catchment in Austria (630 km2), including a hydrological model, a hydraulic model, Random Forest Models for FBMD accumulation risk and Species Distribution Models. Two climate change models (RCPs 4.5 and 8.5) for two future horizons (2060 and 2090) were considered. A graph‐based assessment of the structural connectivity was used to measure the probability of successful dispersal.
Results show a reduction of peak discharge that cascades into a widespread reduction in shear stresses during high flow. The mussel's habitats, defined by hydraulics (i.e. patches with low shear stresses during high flow), are predicted to be stable over the simulated scenarios.
The pressure of FBMDs over the delineated habitat patches is predicted to increase in the future due to the reduced stream transport capacity, reducing up to 25% of the available patches in 2090 for RCP 8.5. Consequently, the mussel's dispersal probability decreases to 44.3%–75.6% of the maximum theoretical value, with the highest drops for short dispersal distances, impacting metapopulation dynamics.
Synthesis and applications. The widespread issue of fine sediment deposition in the streambed will be exacerbated for those catchments where climate change reduces the stream transport capacity. The impacts on the freshwater pearl mussel include habitat loss due to the formation of a new unsuitable substrate, and a decrease in the potential dispersal among the residual habitats. Thus, conservation plans that aim to protect the mussel in the future should focus on the mitigation of fine bed material deposits, prioritizing those subreaches that offer the highest potential for preserving connectivity among suitable habitats.
Zusammenfassung
Die Flussperlmuschel Margaritifera margaritifera bewohnt die Fließgewässersohle, und ist gegenüber Veränderungen des hydrologischen Regimes und der durch übermäßige Feinsedimentablagerung (FSA) verursachten Lebensraumzerstörung empfindlich. Beide Probleme werden durch den Klimawandel potenziell verschärft. Das Verständnis der Auswirkungen des Klimawandels auf zukünftig verfügbaren Lebensraum und das Verbreitungspotential (abhängig von der Bachforelle als Fischwirt) kann die Planung effektiver Schutzmaßnahmen unterstützen.
Um die Auswirkungen des Klimawandels auf diese Muschelart zu prognostizieren, wurde eine semi‐mechanistischer Modellierungsansatz für das Aist‐Einzugsgebiet in Österreich (630 km2) umgesetzt, welche ein hydrologisches Modell, ein hydraulisches Modell, ein Random Forest Klassifikationsverfahren zur Bestimmung des Risikos von Feinsedimentablagerungen und ein Artenverteilungsmodell beinhaltet. Dieser Ansatz wurde dann mit zwei Klimawandelmodelle (RCPs 4.5 und 8.5) für zwei Zukunftshorizonte (2060 und 2090) gekoppelt. Eine spezielle mathematische Analyse der Konnektivität (basierend auf der Graphentheorie) wurde verwendet, um die Wahrscheinlichkeit einer erfolgreichen Ausbreitung zu ermitteln.
Die Ergebnisse der Klimawandelszenarien zeigen eine Reduzierung des Spitzenabflusses, die zu einer Reduktion der Sohlschubspannungen bei hohem Durchfluss führt. Die durch die Hydraulik definierten verfügbaren Lebensräume der Muschel (d. h. Bereiche mit geringen Sohlschubspannungen bei hohem Durchfluss) werden in den simulierten Szenarien als stabil vorhergesagt.
Es wird prognostiziert, dass der Druck von Feinsedimentablagerungen auf die abgegrenzten Lebensraumbereiche in Zukunft aufgrund der reduzierten Transportkapazität zunehmen wird und bis zu 25% der verfügbaren Lebensraumbereiche im Jahr 2090 beim Szenario RCP 8.5 zusätzlich reduziert werden. Folglich sinkt die Ausbreitungswahrscheinlichkeit der Muschel auf 44,3–75,6% des maximalen theoretischen Wertes, mit den stärksten Abnahmen bei kurzen Ausbreitungsdistanzen.
Synthese und anwendungen. Das weit verbreitete Problem der erhöhten Feinsedimentablagerung wird für Einzugsgebiete verschärft, in denen der Klimawandel den Abfluss und damit die Transportkapazität von Flüssen verringert, was sich auf geeignete Lebensräume von Süßwasserarten wie der Flussperlmuschel auswirkt. In diesen Einzugsgebieten sollte sich ein Managementplan zum Schutz der Art und vitaler Metapopulationen auf die Minderung von Feinsedimentablagerungen konzentrieren und den Teilgebieten Priorität einräumen, die das höchste Potenzial für die Erhaltung der Konnektivität zwischen geeigneten Lebensraumbereichen bieten. Die Entwicklung integrierter Modelle ist zwar datenintensiv und erfordert eine interdisziplinäre Integration, ermöglicht jedoch die Verknüpfung von hydrologischen Belastungen und ökologischen Reaktionen und unterstützt die Identifizierung angepasster Managementpraktiken.
The widespread issue of fine sediment deposition in the streambed will be exacerbated for those catchments where climate change reduces the stream transport capacity. The impacts on the freshwater pearl mussel include habitat loss due to the formation of a new unsuitable substrate, and a decrease in the potential dispersal among the residual habitats. Thus, conservation plans that aim to protect the mussel in the future should focus on the mitigation of fine bed material deposits, prioritizing those subreaches that offer the highest potential for preserving connectivity among suitable habitats.
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