Rhine River Research Articles

A critical review of arsenic occurrence, fate and transport in natural and modified groundwater systems in The Netherlands

Arsenic is a common trace element in groundwater and its fate and transport are controlled by combination of (i) natural processes, including redox conditions, salinity and pH, (ii) sedimentary and geochemical environment, and (iii) anthropogenic influences such as groundwater extraction, managed aquifer recharge (MAR), Aquifer Thermal Energy Storage (ATES), and pollution. We investigated the relative influence of these processes by presenting 10 cases from The Netherlands. Our review showed that the primary controlling factor for arsenic mobility in natural coastal dune systems is the redox state of groundwater, with concentrations between 2 and 10 μg/L. Strongly reduced greensands (containing glauconite and, more importantly, associated minerals) exhibited elevated As concentrations, with concentrations up to 40 μg/L. Groundwater systems modified by MAR or those that are influenced by nitrate pollution (NP) showed elevated As concentrations (20–110 μg/L), as a result of either pyrite oxidation (MAR, NP) or reductive dissolution of iron(hydr)oxides (MAR). Increasing temperature at ATES systems may cause mobilization of As at temperatures beyond 25 °C. The highest As concentrations were observed at sites where muddy sediments were recently deposited in surface water bodies (200–820 μg/L), for example in dammed Rhine River tributaries and sand pit lakes south of the city of Amsterdam. The reduction of arsenate to arsenite and competitive desorption during intrusion of polluted water also form important As mobilizing processes. The data for the Netherlands show that high CH4 and NH4 concentrations may form a risk indicator of elevated As levels in some fresh groundwater systems.

Using impact chains for assessing local climate risk—A case study on impacts of extended periods of fluvial low waters and drought on a metropolitan region

As the climate crisis accelerates, the resilience of Europe's aging critical infrastructure systems shifts more and more into focus. However, the rising interconnectedness of critical infrastructure systems and the dependency of their operation on multiple stakeholders makes approaches that target the resilience of isolated infrastructures insufficient and might even result in a decrease of the resilience of the whole system. This need for more resilience thinking in interconnected infrastructure systems has resulted in advances in risk analyses of supply chains and analyses of interdependencies in infrastructure systems from a Critical Infrastructure Protection/Resilience perspective. However, results from such analyses on the level of interconnected infrastructure systems have seldomly be broken down to the level of individual corporate value chains, a necessity as national/regional resilience efforts need to be supported on the local level. In this paper we therefore propose a novel approach for value chain climate risk and vulnerability analysis that combines a participatory, indicator-based approach with a semi-quantitative risk matrix approach to allow linking analyses from national to local scale and supports economic assessment of climate change impacts for individual businesses. This approach has been developed and prototypically applied in a case study in a German metropolitan area located at the Rhine River. The results allow to identify where along the dependency chains of interconnected infrastructure systems, hazards and impacts might manifest, which cascading (economic) impacts result on the level of individual infrastructure operators, and where resilience measures should be taken to be most effective and (cost) efficient.

Trophic impact of Neogobius melanostomus in a restored site on the Old Rhine River (France)

Trophic impact of Neogobius melanostomus in a restored site on the Old Rhine River (France)

Numerical investigations to identify environmental factors for field-scale reactive transport of pathogens at riverbank filtration sites

While induced bank filtration is a proven method for facilitating sustainable drinking water production, it is at risk from surface water contaminations (e.g., pathogens). Induced bank filtration and pathogen transport in groundwater have been studied extensively. However, long-term studies that consider real-world conditions are missing. These conditions include seasonal changes to environmental conditions and waterworks operations. Therefore, to analyze the effect of seasonal changes on the transport of human pathogenic viruses and their indicators in induced bank filtration, concentrations of adenoviruses and pathogen indicators were monitored over 16 months at an active bank filtration plant at the Rhine River, in Düsseldorf (Germany). Based on this data, a 2D groundwater model was created in PFLOTRAN that simulated flow, heat transport, conservative transport of chloride and the resulting electrical conductivity, reactive transport of oxygen and nitrate, and colloid-based transport of coliforms, somatic coliphages, and adenoviruses. The results show that reduced travel time was the key factor determining periods with a low removal of coliforms and somatic coliphages in the aquifer. Travel time was controlled by river level variations during rainy seasons, and the waterworks extraction rates during dry seasons. For adenovirus transport, travel distance in the subsurface appeared to be the key factor, while travel time had no significant impact. Coliform removal increased when the colmation layer permeability decreased, while coliphage and adenovirus removal was unaffected by the colmation layer permeability. Seasonal changes in temperature and oxygen content did not significantly impact the removal of coliphages and adenoviruses in groundwater. Denitrifying conditions correlated with a lowered coliform removal, but the modelling could not establish a connection between denitrifying conditions and coliform removal. Our study showed that removal of pathogens and pathogen indicators at induced bank filtration plants varies greatly in time and space (e.g., for coliforms from 1 to 4 log-levels at 20 m travel distance), and that adenovirus transport differs considerably from transport of coliforms and somatic coliphages

Sample size requirements for riverbank macrolitter characterization

Anthropogenic litter is omnipresent in terrestrial and freshwater systems, and can have major economic and ecological impacts. Monitoring and modeling of anthropogenic litter comes with large uncertainties due to the wide variety of litter characteristics, including size, mass, and item type. It is unclear as to what the effect of sample set size is on the reliability and representativeness of litter item statistics. Reliable item statistics are needed to (1) improve monitoring strategies, (2) parameterize litter in transport models, and (3) convert litter counts to mass for stock and flux calculations. In this paper, we quantify sample set size requirement for riverbank litter characterization, using a database of more than 14,000 macrolitter items (>0.5 cm), sampled for 1 year at eight riverbank locations along the Dutch Rhine, IJssel, and Meuse rivers. We use this database to perform a Monte Carlo based bootstrap analysis on the item statistics, to determine the relation between sample size and variability in the mean and median values. Based on this, we present sample set size requirements, corresponding to selected uncertainty and confidence levels. Optima between sampling effort and information gain is suggested (depending on the acceptable uncertainty level), which is a function of litter type heterogeneity. We found that the heterogeneity of the characteristics of litter items varies between different litter categories, and demonstrate that the minimum required sample set size depends on the heterogeneity of the litter category. This implies that more items of heterogeneous litter categories need to be sampled than of heterogeneous item categories to reach the same uncertainty level in item statistics. For example, to describe the mean mass the heterogeneous category soft fragments (>2.5 cm) with 90% confidence, 990 items were needed, while only 39 items were needed for the uniform category metal bottle caps. Finally, we use the heterogeneity within litter categories to assess the sample size requirements for each river system. All data collected for this study are freely available, and may form the basis of an open access global database which can be used by scientists, practitioners, and policymakers to improve future monitoring strategies and modeling efforts.

Alien species and climate change drive shifts in a riverine fish community and trait compositions over 35 years

Alien fish substantially impact aquatic communities. However, their effects on trait composition remain poorly understood, especially at large spatiotemporal scales. Here, we used long-term biomonitoring data (1984–2018) from 31 fish communities of the Rhine river in Germany to investigate compositional and functional changes over time. Average total community richness increased by 49 %: it was stable until 2004, then declined until 2010, before increasing until 2018. Average abundance decreased by 9 %. Starting from 198 individuals/m2 in 1984 abundance largely declined to 23 individuals/m2 in 2010 (−88 %), and then consequently increased by 678 % up to 180 individuals/m2 until 2018. Increases in abundance and richness starting around 2010 were mainly driven by the establishment of alien species: while alien species represented 5 % of all species and 0.1 % of total individuals in 1993, it increased to 30 % (7 species) and 32 % of individuals in 2018. Concomitant to the increase in alien species, average native species richness and abundance declined by 26 % and 50 % respectively. We identified increases in temperature, precipitation, abundance and richness of alien fish driving compositional changes after 2010. To get more insights on the impacts of alien species on fish communities, we used 12 biological and 13 ecological traits to compute four trait metrics each. Ecological trait dispersion increased before 2010, probably due to diminishing ecologically similar native species. No changes in trait metrics were measured after 2010, albeit relative shares of expressed trait modalities significantly changing. The observed shift in trait modalities suggested the introduction of new species carrying similar and novel trait modalities. Our results revealed significant changes in taxonomic and trait compositions following alien fish introductions and climatic change. To conclude, our analyses show taxonomic and functional changes in the Rhine river over 35 years, likely indicative of future changes in ecosystem services.

СТВОРЕННЯ І РОЗВИТОК СИСТЕМ ВАГОВИХ МІР НІМЕЧЧИНИ, АВСТРІЇ І КРАЇН СКАНДИНАВІЇ

The development of the economy in the territories of modern Germany, the peninsulas of Jutland and Scandinavia, inhabited since ancient times by tribes that spoke Germanic languages, required the use of various measures, the units of which must be related to each other. Since primitive times, the Germans, like other peoples of the world, used the so-called primitive natural measures, the standards of which were borrowed from nature itself. The political disunity of the Germanic tribes led to their lack of a single system of measures. However, a generally accepted standard of weight measures appeared with them. It was a mass of wheat or barley grain. When using units of measure in production and trade, the calculation was based on the numbers of ten and twenty adopted by the Indo-European peoples. In the II–I century B.C., the Romans conquered the territory of modern Germany to the west bank of the Rhine River. Roman colonies were founded there; the Roman system of measures and the monetary system were put into use. The Germanic lands to the east of the Rhine were not part of the Roman Empire. However, due to political ties and trade exchange with the Roman Empire, Roman monetary and weight measures gradually came into use in these lands. In the first centuries A.D., Germanic tribes attacked the Romans. In the 5th century, the Western Roman Empire fell. The territory of its provinces was conquered by Germanic tribes who created independent kingdoms here. In the 8th century, Charlemagne, the ruler of one of them, namely Frankish, united the former territories of the Western Roman Empire under his authority. In the empire of Charlemagne, a single system of measures was created, in which Roman and German measures were combined. In particular, instead of the Roman siliqua, which is a carob bean, the mass of a barley grain was adopted as the standard of weight. The calculation of units according to this system was conducted not only with the help of Roman numerals for 6 and 12, but also by dividing by the two system and using the decimal system. Charlemagne’s weight measures included units of coin and trade weight. Subsequently, as the analysis of the sources shows, it was on the basis of the Carolingian units of trade weight that systems of weight measures were created in the territories of Germany, Austria and the Scandinavian countries during the Middle Ages. In the 9th century, the Carolingian empire fell apart. In the 10th century, Otto I, the king of Germany, having united under his authority certain territories of Western Europe, announced the foundation of the Holy Roman Empire of the German nation. Later, this state gradually fell apart into separate possessions, the rulers of which introduced their own monetary and weight measures. They were based on the division into marks. Initially, this monetary weight unit was equal to 2/3 of a Roman pound. Subsequently, various stamp weight standards appeared in German lands. From the 15th century, the gold and silver mass standards of the Cologne mark are being distributed in Western Europe. In the second half of the XIX century, the political unification of Germany took place, which coincided with the introduction of the international metric system in the territories of Germany, Austria and the Scandinavian countries.

River basins and deltas need a second game-change

River basins and deltas can be considered as complex systems with dynamics resulting from natural processes. These dynamics have generated many ecosystem services, but they are also erratic in nature.
 Since the industrial revolution, the belief has emerged that these systems can be controlled, thereby suppressing the erratic nature of rivers and deltas and maximizing economic benefits. This has led to a game change in the development of rivers and deltas: until the mid-19th century, the natural system was dominant and economic and urban development followed; after the mid-19th century, economic and urban development became dominant and the river and delta systems were increasingly adapted to the new economic and urban realities. The result of this first game change was the disappearance of sufficient room for the natural dynamics of river and delta systems. This has led to major problems in the current times of climate change, which can only be tackled with a second game change, which takes more into account the natural dynamics of the river and delta systems and offers more space for these dynamics.
 An example of what this second game change could look like is a proposal for the reorganization of the main discharge of the Rhine and Maas rivers in the Dutch Rhine-Meuse delta. This reorganization has major consequences, but also offers new opportunities for the water system, as well as for the natural environment and for port development, urban development, and the necessary energy transition. For this new game change, design explorations are necessary to investigate how a new synergy can be achieved by combining all these aspects.

Machine Learning Predictions of Oil Yields Obtained by Plastic Pyrolysis and Application to Thermodynamic Analysis.

Chemical recycling via thermal processes such as pyrolysis is a potentially viable way to convert mixed streams of waste plastics into usable fuels and chemicals. Unfortunately, experimentally measuring product yields for real waste streams can be time- and cost-prohibitive, and the yields are very sensitive to feed composition, especially for certain types of plastics like poly(ethylene terephthalate) (PET) and polyvinyl chloride (PVC). Models capable of predicting yields and conversion from feed composition and reaction conditions have potential as tools to prioritize resources to the most promising plastic streams and to evaluate potential preseparation strategies to improve yields. In this study, a data set consisting of 325 data points for pyrolysis of plastic feeds was collected from the open literature. The data set was divided into training and test sub data sets; the training data were used to optimize the seven different machine learning regression methods, and the testing data were used to evaluate the accuracy of the resulting models. Of the seven types of models, eXtreme Gradient Boosting (XGBoost) predicted the oil yield of the test set with the highest accuracy, corresponding to a mean absolute error (MAE) value of 9.1%. The optimized XGBoost model was then used to predict the oil yields from real waste compositions found in Municipal Recycling Facilities (MRFs) and the Rhine River. The dependence of oil yields on composition was evaluated, and strategies for removing PET and PVC were assessed as examples of how to use the model. Thermodynamic analysis of a pyrolysis system capable of achieving oil yields predicted using the machine-learned model showed that pyrolysis of Rhine River plastics should be net exergy producing under most reasonable conditions.

Reconstruction of the 1374 Rhine river flood event around Cologne region using 1D-2D coupled hydraulic modelling approach

Reconstructions of the most severe historic flood events contribute to improved quantification of design discharges corresponding to large return periods. Reducing the uncertainty of design discharges has a great significance in constructing proper flood defences to protect the hinterland from future flooding. However, reconstructions of the peak discharges of such historic flood events are generally associated with large uncertainties, which arise from the accuracy of the historic topography, hydraulic roughness of the river channels and floodplains, and the historic hydrograph shape. This study sets up a one dimensional-two dimensional (1D-2D) coupled hydraulic model, stretching from the upstream of Bonn at Remagen to downstream of Düsseldorf, Germany, with the length of 113 km to reconstruct the maximum discharge of the 1374 flood event (Qmax,1374), which is considered to be the largest flood of the last millennium in the Lower Rhine catchment. An uncertainty analysis was performed by adopting different river bed levels and roughness values in order to estimate the influence of these uncertainties on the reconstructed peak discharge. The upstream discharge wave was varied corresponding to a wide range of peak discharges from 12,000 to 24,000 m3/s. The resulting Qmax,1374 was determined of between 14,400 and 18,500 m3/s, were then used in a flood frequency analysis to determine the design discharges corresponding to different return periods. Compared to the design discharge computed with previous estimations of the 1374 peak discharge, we found a significant reduction of 2,000 m3/s in the design discharge corresponding to a 100,000 year return period, which is the maximum safety standard adopted in the Dutch water policy for some downstream dike sections.

The Tamins rock avalanche (eastern Switzerland): timing and emplacement processes

The Tamins rock avalanche lies adjacent to the Flims rock avalanche, the largest in the Alps. Its deposit forms a ridge across the Rhine Valley just downstream of the confluence of the Vorderrhein and Hinterrhein rivers. The deposit is dominated by a 1.6-km-long longitudinal ridge, Ils Aults, and two roughly 600-m-long transverse ridges. Several extensional scarps bear witness to spreading of the deposit. A breach through the deposit, where the Rhine River presently flows, reveals a carapace and intense fragmentation. Exposure dating using cosmogenic 36Cl yields an age of 9420 ± 880 years. This suggests that the Tamins event occurred in a time frame similar to the Flims event but was slightly earlier than the Flims rock avalanche, as also required by stratigraphic relationships. 3D volume modeling reveals bulking of only 14%. The motion of the rock avalanche seems to have occurred first as a flexible block, which underwent fragmentation and simple shearing where the top moved faster than the bottom. The ensuing spreading led to the formation of extensional scarps. There is no identified weak layer along the sliding surface; nevertheless, modeling suggests a friction angle of 10°.

Efficacy of Longitudinal Training Walls to Mitigate Riverbed Erosion

AbstractThe Waal Branch of the Rhine River has eroded over the last 150 years following channel straightening and narrowing. In 2014–2015 a pilot project replaced existing groynes over an 11 km long reach with three longitudinal training walls (LTWs) to mitigate channel bed erosion, among other purposes. Walls are lower than the river bank and split the flow between a primary and an auxiliary channel, which are hydraulically connected during floods. Water enters the auxiliary channel at three elevations (from bottom to top): via an entrance weir, through inter‐wall notches, and over the wall. Bathymetry and discharge data were collected for 5 years after construction, which is a first indication that longitudinal dams can help mitigate channel bed erosion and analyzed to understand how the walls partition water and sediment and whether erosion is mitigated by LTWs. As the river discharge increases, a larger fraction of flow is diverted from the primary channel into the auxiliary channel. After a flood, sediment is deposited in the primary channel near the upstream end of each wall and localized scour occurs where the auxiliary channel rejoins the primary channel. Between floods, the accumulated sediment disperses and scour pits tend to fill. We observe a net‐accumulation of sediment in the study domain 5 years after construction. Erosion is best mitigated when weir flow is minimized to keep bed material in the primary channel, but weir flow remains important at lower flows for ecological purposes.

Raspberry Pi Reflector (RPR): A Low‐Cost Water‐Level Monitoring System Based on GNSS Interferometric Reflectometry

AbstractAlthough reflectometry is not the primary application of Global Positioning System (GPS) and similar Global Navigation Satellite Systems (GNSS), fast‐growing GNSS tracking networks has led to the emergence of GNSS interferometric reflectometry technique for monitoring surface changes such as water level. However, scientific‐grade or geodetic GNSS instruments are expensive, which is a limiting factor for their prompt and more widespread deployment as a dedicated environmental sensor. We present a prototype called Raspberry Pi Reflector (RPR) that includes a low‐cost and low‐maintenance single‐frequency GPS module and a navigation antenna connected to an inexpensive Raspberry Pi microcomputer. A unit has been successfully operating for almost 2 years since March 2020 in Wesel (Germany) next to the Rhine river. Sub‐daily and daily water levels are retrieved using spectral analysis of reflection data. The river level measurements from RPR are compared with a co‐located river gauge. We find an Root‐Mean‐Square Error (RMSE) of 7.6 cm in sub‐daily estimates and 6 cm in daily means of river level. In August 2021, we changed the antenna orientation from upright to sideways facing the river. The RMSE reduced to 3 cm (sub‐daily) and 1.5 cm (daily) with the new orientation. While satellite radar altimetry techniques have been utilized to monitor water levels with global coverage, their measurements are associated with moderate uncertainties and temporal resolution. Therefore, such low‐cost and high‐precision instruments can be paired with satellite data for calibrating, validating and modeling purposes. These instruments are financially (<US$ 150 as of November 2021) and technically accessible worldwide.

Upstream-downstream asymmetries of drought impacts in major river basins of the European Alps

The European Alps, despite being Europe's water towers, are increasingly affected by droughts. In recent decades, when climate warming has intensified, drought impacts have illustrated the regions' vulnerability. Improved knowledge on the spatial distribution of drought impacts from high elevation headwater regions down to plateau and foothill areas is of tremendous importance to understand socio-economic drought dimensions. The region has an exceptional data availability including archived drought impact information. It is therefore a good test bed for the often-assumed general hypothesis that drought impacts occur more often downstream. The aim of this study was to investigate whether upstream-downstream differences in the distribution of drought impacts exist in the four major river basins of the European Alps - Rhine, Rhone, Po and Danube. Two different classifications were developed to divide these basins in up- and downstream areas. We based the first classification on the distances to the main sink, and the second classification on human influence. The EDIIALPS database provided qualitative data to analyze the distribution patterns of reported drought impacts from 2000 to 2020. The results suggest a strong regional variability regarding the temporal and spatial distribution of drought impacts within the individual basins. But they support the general hypothesis: for both classifications the number of drought impacts per area is higher in downstream regions. For the classification based on distances differences are statistically significant for the Rhine and Danube basin. Further, the analysis of the drought indices SPI-6 and SPEI-6 revealed that the drought event does not have a large impact on the upstream-downstream differences. The study provides support for the existence of upstream-downstream asymmetries, but most importantly, the spatial distributions of drought impacts found in the four major river basins of the European Alps highlight the need for a network based analysis with more consistent impact data within river basins. Climate change and enhanced cascading effects likely increase these asymmetries and consequently future drought management strategies should take them into account.

Toward Robust River Plastic Detection: Combining Lab and Field‐Based Hyperspectral Imagery

AbstractPlastic pollution in aquatic ecosystems has increased dramatically in the last five decades, with strong impacts on human and aquatic life. Recent studies endorse the need for innovative approaches to monitor the presence, abundance, and types of plastic in these ecosystems. One approach gaining rapid traction is the use of multi‐ and hyperspectral cameras. However, most experiments using this approach were in controlled environments, making findings challenging to apply in natural environments. We present a method linking lab‐ and field‐based identification of macroplastics using hyperspectral data (1,150–1,675 nm). Experiments using riverbank‐harvested macroplastics were set up in a laboratory environment, and on the banks of the Rhine River. Representative pixel selections of eleven lab‐based images (n = 786,264 pixels) and two field‐based images (n = 40,289 pixels) were used to analyze the differences between these environments. Next, classifier algorithms such as support vector machines (SVM), spectral angle mapper (SAM) and spectral information divergence (SID) were applied, because of their robustness to varying light conditions and high accuracies in mapping spectral similarities. Our results showed that SAM classifiers are most robust in separating plastic pixels from background elements. By applying lab‐based data for plastic detection in field‐based images, user accuracies for plastics to up to 93.6% (n = 8,370 plastic pixels) were attained. This study provides key fundamental insights in linking lab‐based data to plastic detection in the field. With this paper we aim to contribute to the development of future spectral missions to detect and monitor plastic pollution in aquatic ecosystems.

Vegetation and peat accumulation steer Holocene tidal–fluvial basin filling and overbank sedimentation along the Old Rhine River, The Netherlands

AbstractIn the transformation from tidal systems to freshwater coastal landscapes, plants act as eco‐engineering species that reduce hydrodynamics and trap sediment, but nature and timing of the mechanisms of land creation along estuaries remains unclear. This article focuses on the Old Rhine estuary (The Netherlands) to show the importance of vegetation in coastal landscape evolution, predominantly regarding tidal basin filling and overbank morphology. This estuary hosted the main outflow channel of the river Rhine between ca 6500 to 2000 cal bp, and was constrained by peat during most of its existence. This study reconstructs its geological evolution, by correlating newly integrated geological data and new field records to varying conditions. Numerical modelling was performed to test the inferred mechanisms. It was found that floodbasin vegetation and resulting organic accumulation strongly accelerated back‐barrier infill, by minimizing tidal influence. After tidal and wave transport had already sufficiently filled the back‐barrier basin, reed rapidly expanded from its edges under brackish conditions, as shown by diatom analysis and datings. Reed growth provided a positive infilling feedback by reducing tidal flow and tidal prism, accelerating basin infilling. New radiocarbon dates show that large‐scale crevassing along the Old Rhine River – driven by tidal backwater effect – only started as nutrient‐rich river water transformed the floodbasin into an Alder carr in a next phase of estuary evolution. Such less dense vegetation promotes crevassing as sediments are more easily transported into the floodbasin. As river discharge increased and estuary mouth infilling progressed, crevasse activity diminished around 3800 to 3000 cal bp, likely due to a reduced tidal backwater effect. The insights from this data‐rich Holocene study showcase the dominant role that vegetation may have in the long‐term evolution of coastal wetlands. It provides clues for effective use of vegetation in vulnerable wetland landscapes to steer sedimentation patterns to strategically adapt to rising water levels.

Effect of sediment form and form distribution on porosity: a simulation study based on the discrete element method

Porosity is one of the key properties of dense particle packings like sediment deposits and is influenced by a multitude of grain characteristics such as their size distribution and shape. In the present work, we focus on the form, a specific aspect of the overall shape, of sedimentary grains in order to investigate and quantify its effect on porosity, ultimately deriving novel porosity-prediction models. To this end, we develop a robust and accurate simulation tool based on the discrete element method which we validate against laboratory experiments. Utilizing digital representations of actual sediment from the Rhine river, we first study packings that are composed of particles with a single form. There, porosity is found to be mainly determined by the inverse equancy, i.e., the ratio of the longest to the smallest form-defining axis. Only for small ratios, additional shape-related properties become relevant, as revealed by a direct comparison to packings of form-equivalent but smooth ellipsoids. Since sediment naturally features form mixtures, we extend our simulation tool to study sediment packings with normally-distributed forms. In agreement with our single form studies, porosity is found to depend primarily on the inverse of the mean equancy. By supplying additional information about a second form factor and the standard deviations, we derive an accurate model for porosity prediction. Due to its simplicity, it can be readily applied to sediment packings for which some measurements of flatness and elongation, the two most common form factors, are available.Graphical abstract

Spatio-temporal differences dominate suspended sediment dynamics in medium-sized catchments in central Germany

Suspended sediment transport, dominating material export from lowland river systems, is highly variable in space and time. Since suspended sediment transport can have adverse effects on human infrastructure, targeted management is imperative. To achieve this, a thorough understanding of suspended sediment dynamics is needed, but requires long-term monitoring data. Despite studies investigating suspended sediment dynamics on decadal time scales, an assessment of the spatio-temporal variability across adjacent river catchments is still lacking.To fill this gap, we analyse suspended sediment transport at twelve stations along German upland rivers, monitored on a daily basis for 28 to 54 years. All monitoring stations belong to the Rhine (Lahn, Lippe, Main, and Neckar) and Weser river systems (Fulda, Leine, Werra, and Weser) and have contributing areas between 2500 and 22,000 km2. Although located in comparable topo-climatic settings, average sediment yield for the monitoring period varied more than fourfold. Covering the range of 5.9 to 28.7 t km−2 yr−1, we found the highest and lowest suspended sediment yields for the Neckar and Lippe catchments, respectively. Using two different streamflow separation approaches, we estimated the contribution of stormflow discharge to total sediment transport to fall between 73 and 85 % in the Neckar and Lahn rivers while remaining ~15 % lower for the remaining catchments. Investigating the relevance of extreme events, we found the share of total suspended sediment load transported during the ten largest events to vary between ~28 % for the Neckar and ~8 % for the Lippe and Werra catchments. These events were predominantly characterized by clockwise hysteresis loops that hint to in-channel reworking as a significant material source, with the exception of the Neckar stations where anti-clockwise hysteresis patterns prevailed. Here, the hysteresis analysis indicates sediment delivery from more distant sources in the headwater regions, likely related to elevated rainfall intensities and the susceptibility of the escarpment of the Swabian Alb towards landsliding. We conclude that the combined effect of varying rainfall amounts and intensities, the fraction of steeper slopes as well as lithological differences explain the across-catchment variability on multiple time scales that is further modulated by river management practices.

Morpho-sedimentary characteristics of Holocene paleochannels in the Upper Rhine alluvial plain, France

Abstract. The French Upper Rhine alluvial plain is characterized by a complex system of paleochannels inherited from Late Glacial to Holocene fluvial dynamics of the Rhine and Ill river systems, among other smaller rivers. These paleochannels represent valuable archives for understanding and reconstructing the fluvial and landscape evolution of the area. However, the Holocene temporal trajectories of the paleochannels, in response to a range of environmental changes, remain poorly understood. This study presents a detailed and systematic mapping and characterization of an extensive network of paleochannels spanning the entire width (19 km) of a reach of the central French Rhine plain. Based on qualitative and quantitative lidar analysis, field investigations, and provenance investigations of paleochannel infill sequences, five distinct paleochannel groups (PG 1 to PG 5) were identified in the study area. These paleochannel groups differ considerably regarding their channel patterns, morphological characteristics, and sedimentary sources of the infilling sediments. The interpretation of the different datasets indicates that the development of these different paleomorphologies is attributed to significant changes in hydro-geomorphodynamic processes in the area during the Holocene, especially lateral migrations of the Rhine and Ill rivers. The findings reported here are promising and will have significant implications for reconstructing the long-term (Late Glacial to Holocene) evolution of the Upper Rhine fluvial hydrosystem in response to various controlling factors.

Technology-critical elements in Rhine sediments - A case study on occurrence and spatial distribution

Despite their presence in almost every technical device, little is known about the occurrence, distribution, and fate of technology-critical elements (TCEs) within the environment. Due to high economic demands and short product lifespans as well as low recycling rates, many TCEs appear to become emerging contaminants.Within the scope of this work, 57 sediment samples from the German part of the Rhine river, as well as various tributaries, were collected to study the occurrence and distribution of TCEs. This specific catchment area has consistently been subjected to strong anthropogenic influences over the last century. Hierarchical cluster analysis, as well as principal component analysis were used to gain first insights into the spatial distribution and possible sources of TCEs along the Rhine.Obtained mass fractions in conjunction with corresponding geoaccumulation indices (Igeo) provide first indications of a possible enrichment along the Rhine for the TCEs of interest (Ga, Ge, Nb, In, Te, rare earth elements, and Ta). Especially the mass fractions of Zn, Ge, In, La, Sm, and Gd exhibit significant anthropogenic inputs. For stations characterized by high Ge and In mass fractions, element fingerprints imply possible atmospheric deposition stemming from e.g. combustion processes. Distinct anomalies of La and Sm most likely originate from discharges located at the city of Worms into the Upper Rhine. Statistical analysis of all analyzed 55 elemental mass fractions revealed similar behavior of TCEs compared to classical heavy metals. Diffuse as well as point sources of TCEs are likely. As a result, this study provides further insight into the role of TCEs as potential emerging contaminants in the environment.