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Land use and water resource management influence the suspended sediment concentration (SSC) in rivers. Fine sediments are an important driver for river development, even in coarse-material-rich rivers. In this study, the sediment rating curve approach is modified to predict SSC several river-km downstream of a sampling site. Further, the prediction is improved by adding sediment input, storage, and dilution effects through relevant anthropogenic measures through a model identification approach. Thus, the impact of the most severe anthropogenic measures, damming and changes in the length of a channel section for the Rur River, could be identified. Further, the impact of describing parameter changes for those measures on the SSC can be computed and considered in future water resource management. In this approach, particle swarm optimization was used to fit parameters in permutable test- and training data sets to identify linear extensions to the sediment rating curve. The input data consists of (1) SSC, which was obtained by sampling along the river section four times a year over approximately two years, (2) discharge data from river gauges supplemented by rainfall-runoff modeling between stations, (3) rainfall data from meteorological stations, and (4) sub-catchment characteristics like river section length and erosivity obtained with GIS. Via incorporating the river section length and sediment deposition in response to damming, we reduced the RMSE (root mean squared error) from 152.27 to 131.83% with a p-value of 0.073 in the Wilcoxon Signed Rank Test. Further integration of sub-catchment parameters like erosivity led to overfitting and decreased prediction accuracy. A catchment-wide prediction was achieved, but sub-catchments operate on different spatial scales with different connectivity behavior, which restricts the transferability of the equation. SSC-Q hystereses provide the first indications of characteristic sediment sources and were used to discuss connectivity behavior within the study area. They are recommended as part of a (sub-) catchment characterization for further studies.

Microplastics in the environment are a relatively new form of anthropogenic contamination. Right now, the research focus is on the detection of microplastic accumulation in different environmental compartments and understanding the processes that have led to its transport. Detailed information on microplastics in floodplain areas and their distribution in depth are still missing to better understand accumulation points. Therefore, this study presents on the one hand microplastic detection in fluvial sediments from nine sampling sites along a river course. Polymers were determined with infrared spectroscopy and additional sedimentary analysis of the grain size and heavy metal concentration was performed. In total, there was less microplastic in the upper than in the lower river course and slip-off slopes were identified as accumulation hotspots also in deeper sediment layers. Mostly, microplastic particles were detected in fine sediment and heavy metal concentrations along the river were similar to those of microplastics. On the other hand, besides the spatial distribution of microplastics and accumulation in floodplain areas, microplastic analysis offered information in a sedimentary context. Sedimentation rates (0.29-4.00 cm a-1) and patterns between temporal deposition and microplastic polymers were identified. The basis for the development of a dating method by detection of MPs in sediments was thus established. Microplastics as a contaminant provide, in addition to the identification of deposition areas, further data in a temporal and sedimentary perspective.

The sediments of the artificial Urft reservoir preserve a century of environmental information due to undisturbed sedimentation conditions. The Urft reservoir is located in the Eifel Mountains in western Germany and was built between 1900 and 1905. At the time of its construction, the Urft reservoir was the largest reservoir (45.51 million m³) and drove, with 12 MW, the most powerful water storage power plant in Europe. During construction works in November 2020, the reservoir was nearly completely drained. This offered the unique possibility to analyse the sediment volume and the composition deposited during the last 115 years.We used high resolution maps with a scale of 1:1,000 from 1898 which were compiled to calculate the original storage volume of the reservoir. To assess the present-day surface, the entire lake area was photogrammetrically surveyed using an Unmanned Aerial Vehicle (UAV). Additionally, 10 drill cores were retrieved in 2020 to quantify the anthropogenic influence on the sediments in the form of mining-induced sediment-bound pollutants (e.g., heavy metals) and to relate this to the history of use in the catchment area. Furthermore, microplastics were studied in the sediments. To derive the sediment ages, a detailed Cs-137 chronology was created for one of the cores.In summer 2021, the northern Eifel Mountains were impacted by a catastrophic flooding event, resulting in massive destructions in the catchment of the Urft and strong relocation of sediments in the floodplain. To assess these geomorphologic changes in the Urft reservoir, the water level was lowered again in December 2021. Consequently, an additional digital elevation model was produced by UAV surveying. Furthermore, additional sediment cores were taken to get information on changes in the sediment composition due to the flood event. In the upper part of the reservoir, up to 30 cm of sediments were deposited in summer 2021 while channels below the water surface experienced strong modifications.

Extreme precipitation and discharge between July 13th and 16th 2021 caused serious flooding with bank erosion, including damages to infrastructure and buildings nearby the Eifel mountain region. Especially the small town of Stolberg and Eschweiler in the Inde River catchment were heavily affected. On-site investigation along the Inde River and its tributary, the Vichtbach creek, after the flood event show that mainly coarse sediments were remobilized and accumulated in the upper and middle reaches. The water masses mobilized not only sediments including gravel but also large objects like broken down trees and cars. In contrast, silty sediments were deposited in the lower reaches.The Stolberg region is a former mining area with related industries resulting in contaminated soils and tailings close to the floodplains (Esser et al. 2020). Therefore, our investigations also focus on pollution by sediment-bound heavy metals and their distribution in the floodplains before and after this event. Flood sediment samples were taken immediately after the extreme flood event. Based on the results of flood-related pollution monitoring, conducted between 2016 and 2019 (Esser, 2020), the impact of the extreme event in July can be evaluated. During the July flood event, an exceptional amount of pollutants was remobilized. In addition to an increase in pollutants on the modern floodplain, wider areas of older and higher floodplains (Altauen) were also affected.Esser, V. (2020): Untersuchungen zur fluvialen Morphodynamik und zur rezenten Schadstoffausbreitung in Flusssystemen - Beispiele aus der Grenzregion Belgien, Niederlande und Deutschland. PhD-Thesis, RWTH Aachen University.Esser, V., Buchty-Lemke, M., Schulte, P., Podzun, L.S., Lehmkuhl, F. (2020): Signatures of recent pollution profiles in comparable Central European rivers - Examples from the International River Basin District Meuse. Catena 193: 104646. https://doi.org/10.1016/j.catena.2020.104646

Background Over the last 200 years, the courses of most European rivers have experienced significant irreversible changes. These changes are connected to different kinds of anthropogenic river use and exploitation, which have varied from running water mills and rafting to large-scale hydroelectric power plants, industrial water withdrawal and flood protection measures. Today, in most developed countries, water quality and ecological river development are important factors in water management. The aim of this study is to evaluate the specific impacts of different time periods during the last 200 years on river courses and their effects on current river management using the example of the 165-km-long German Rur River (North Rhine-Westphalia). The Rur River is a typical central European upland-to-lowland river whose catchment has been affected by various phases of industrial development. Methods In this study, a range of morphological changes over the last 200 years are determined based on historic maps and up-to-date orthophotos. River length, sinuosity, oxbow structures, sidearms and the number of islands are used to investigate human impact. The results are correlated with historic time periods. Results This analysis shows that river straightening increases, especially during the Industrial Revolution, even without direct hydraulic channelization. The period and grade of river straightening have a direct morphodynamic impact on today’s river restorations. Since the Rur River is a typical upland-to-lowland river, the results show an additional impact by geofactors, such as landform configurations. Conclusions Morphodynamic development is correlated with five historic periods of industrial development between 1801 and 2019 up to the introduction of the EU—Water Framework Directive (EU-WFD). Each period shows a different influence on the watercourse, which is connected with human intervention. Even if worldwide comparisons show that the five historical phases differ slightly in their timing between regions, they are applicable to other study areas.

Environmental sciences Europe : ESEU 33, 15 (2021). doi:10.1186/s12302-021-00460-8, Published by Springer, Berlin

EGU General Assembly 2021, vEGU21, online, 19 Apr 2021 - 30 Apr 2021; Geophysical research abstracts 23, EGU21-148 (2021). doi:10.5194/egusphere-egu21-148 special issue: "EGU General Assembly 2021", Published by European Geophysical Society, Katlenburg-Lindau

Background Over the last 200 years, most European river courses experienced significant irreversible changes. These changes were connected with different kinds of anthropogenic river use and exploitation, which varied from running water mills and rafting to large-scale hydroelectric power plants, industrial water withdrawal and measures for flood protection. Today, in most of the developed countries water quality and ecological river development are stakeholders in water management. The aim of the following study is to evaluate the specific impact of different time periods during the last 200 years on river courses, and its effects on the current river management using the example of the 165 km long German Rur River (North Rhine-Westphalia). The Rur River is a representative central European upland to lowland river, whose catchment has been affected by various phases of industrial development.MethodsIn this study, large-scale morphological changes over the last 200 years are determined based on historic maps and up-to-date orthophotos. The indicators river length, sinuosity, oxbow structures, sidearms and the number of islands are used to investigate human impact. The results are correlated with historic time periods.ResultsThis analysis shows that river straightening does increase especially during the industrial revolution, even without direct hydraulic channelization, which applies not only to the study area but also to further examples worldwide. The period and grade of river straightening has a direct morphodynamic impact on today’s river restorations. Since the Rur River is a typical upland to lowland river, the results show additional impact of geo-factors, like landform configurations.ConclusionsThe morphodynamic development is correlated with five historic periods between 1801 and 2019 of industrial development up to the introduction of the EU - Water Framework Directive (EU-WFD). Each period shows different influence on the watercourse which is connected with human intervention. Even if worldwide comparisons show that the five historical phases differ slightly in time between regions, they are applicable to other study areas.

Recultivation is a strategy for restoring near-natural landscape systems in anthropogenically influenced environments. Especially in post-mining landscapes after open pit mining, recultivation gives opportunities and potential for near-natural landscape modeling. In order to evaluate the success of the applied measures, biological monitoring approaches with a focus on biodiversity are often carried out. However, the loss of natural soils, which are the result of long-term formation, is an irreversible damage to the pedosphere. The natural soil functions must be completely re-established and it is difficult to examine its success. In our study we therefore investigated initial soil formation in an morphodynamically active artificial river valley, modeled and constructed with a recultivation substrate called “Forstkies”. The study area is located in the catchment of the Inde River (North Rhine-Westphalia, Western Germany), which is part of the international River Basin District Meuse. Due to the progress of the open pit lignite mining, a 5 km long river course had to be relocated. With the aim of creating a near-natural landscape and an appropriate development corridor for the river, a ~ 12 km long river relocation was designed. The artificial river section "Neue Inde" is still geomorphologically naïve and characterized by temporary, highly energetic morphodynamic processes resulting in strong erosion processes in the river bed and the surrounding area. To characterize the morphodynamics and to detect initial soil formation processes, we analyzed a transect of seven soil profiles. The transect includes floodplains and slope areas further away from the river. Allochthonous flood sediments can be differentiated from the underlying artificial Forstkies sediments by inherited contamination of the heavy metals Pb, Zn and Cu. By means of common soil parameters (grain size, CaCO3, total organic carbon, pH value and sediment colors) and geochemical weathering indices, first initial post-sedimentary alterations can be detected. The quality of the soils is absolutely appropriate to the state of development. The results obtained can be helpful for the planning of future renaturation in post-mining landscapes.

Rivers are strongly influenced by humans. As the natural occurrence of trace elements (TEs) is controlled by the geological setting, elevated contents of TEs are caused by anthropogenic activities. TEs can be adsorbed at fine sediments and (re-)mobilized, transported and accumulated at the riverbed and as overbank deposits on the floodplains. Thus, rivers are the transition system for pollutants between their source areas and the depositional areas. To investigate the recent distribution of TEs related to different impact factors, suspendible riverbed sediments of three rivers with neighboring catchments (catchment size each ± 350 km2) within the International River Basin District Meuse (border triangle between Belgium, the Netherlands and Germany) were analyzed. The aim is to compare the variability of pollution profiles (longitudinal TE distribution of sediment samples along the river) of three rivers, that are representative for central European foothills to lowland rivers, with both similar natural settings and disparate human impact factors, and to identify and analyze the ‘fingerprint’ of each river. Hence, a characterization of the individual pollution characteristics of the rivers, with past and recent TE sources, is achieved, which is applicable to other rivers with a similar land use history. The suspendible riverbed sediments of all three rivers show high contents of Cr (71.3–846.7 mg kg−1), Ni (15.2–61.9 mg kg−1), Cu (10.7–357.8 mg kg−1), Zn (186.35–6,571 mg kg−1), As (3.05–25.25 mg kg−1), Cd (1.1–22.8 mg kg−1), Sn (0.325–36.1 mg kg−1), and Pb (16.6–1,116 mg kg−1). Most of the concentration values exceed European supraregional background levels. The three catchments are characterized by high geogenic background contents due to the occurrence of ore and coal deposits and urban sources. However, each river shows different characteristics, driven by the natural setting and the individual anthropogenic activities. The pollution profiles show heterogeneous patterns along the river, with both, increasing and decreasing TE values and pollution hotspots. The used sampling method after Lambert and Walling (1988) is very well suitable for comparable rivers with a heterogeneous riverbed composition and enables to analyze characteristics of longitudinal pollution profiles in different river catchments. The TEs contents of the suspendible riverbed sediments of the three catchments are anthropogenically elevated. While urbanization causes heterogeneous patterns and moderately elevated contents of TEs, concentrations caused by past exploitation and processing of ore and coal and other related industries exceed other possible pollution sources. Today, the historical pollution sources stored in the sediments still have a major impact on the river systems, while modern pollution sources contribute to a minor extent.