HS9.2

Since 60 years, a large amount of data has been acquired to survey river sediment quality, especially concerning regulatory trace metals such as Cd, Cr, Cu, Hg, Ni, Pb, and Zn. Large-scale syntheses are still rare and show some limits to assess the effectiveness of public regulations and the river systems' resilience. Based on a sediment contamination database comprising more than 12,000 samples, we propose a first attempt to decipher spatio-temporal trends of metal contamination along seven major rivers in Western Europe (Garonne-Lot, Loire, Meuse Rhine, Rhone, Scheldt and Seine Rivers). Facing heterogeneous sampling and analytical methods on different sediment matrices (bed and flood deposits – BFD, suspended particulate matter – SPM, dated sediment cores – DSC), this work investigates the effect of analytical protocols, spatial and temporal factors on metal concentration trends. At a large scale, an increase in metal concentrations (especially for Cd, Pb and Zn) is reported along most of the investigated rivers. It appears closely related to major urban-industrial hotspots (Paris-Rouen corridor on the Seine River, Bonn-Duisburg corridor on the Rhine River, etc.) and to the geology of each watershed, both influencing the regional sediment quality. Former mining and metallurgical districts, generally located in crystalline areas, also caused high metal concentrations on the long term (Upper Loire River, Middle Meuse River, Lot River). A global decrease of metal concentrations is observed in all river sections since the 1960s-1970s onwards, in response to European and national regulations, and to socio-economical changes affecting urban-industrial areas. The high influence of the location of the samples along the rivers and the decade of sampling is confirmed by a Factor Analysis of Mixed Data (FAMD). Secondary factors such as the influence of the sediment matrix type (BFD, SPM and DSC) and the different digestion procedures prior to elemental analysis also explained significant differences for Cr, Cd, Cu, Pb, or Zn, although this can also be locally balanced by the substratum (i.e. for alkaline rivers). This approach points out the limitations of the available data, particularly regarding the need of regional geological backgrounds and the more systematic acquisition of ancillary data such as grain-size and TOC. It also provides critical clues to intercompare metal sediment pollution in rivers at large spatial and temporal scales worldwide.

How to cite: Dendievel, A.-M., Grosbois, C., Ayrault, S., Evrard, O., Coynel, A., Debret, M., Gardes, T., Euzen, C., Schmitt, L., Chabaux, F., Winiarski, T., van Der Perk, M., and Mourier, B.: Progress towards an international comparison of river sediment pollution: Key factors influencing metal concentrations along seven Western European Rivers (1945-2020), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2928, https://doi.org/10.5194/egusphere-egu22-2928, 2022.

In urbanised areas, the surface runoff generated by heavy rainfall events mobilise particles carrying contaminants such as heavy metals and polycyclic aromatic hydrocarbons. Those particle-bound pollutants (PBPs) are likely to reach streams through combined sewer overflows or stormwater discharges. Hence, stormwater runoff from urban impervious surfaces affects hydrological and sedimentological conditions of urban streams. Therefore, it is necessary to assess sediment sources, pathways and storage in urbanised catchments to improve sediment management and receiving water quality.

This study aimed at characterising the impacts of urban wet weather discharges (UWWDs) along a stream bed. Thus, the intrusion of fine sediments and the concentration of heavy metals was evaluated along a downstream urbanisation gradient. Our study area is a small catchment (Lockwitzbach, 84 km²) located in Dresden, Germany. It has a main stream length of 29 km and its land use is dominated by non-irrigated arable land (40%), pastures (21%) and urban areas (14%). The urbanised area is clustered towards downstream. In this study we focused on the last 7 km within the city of Dresden, where 9 combined sewer overflows and 19 storm water outlets are located. The urban catchment was subdivided into 9 sewersheds considering the characteristics of the urban drainage network.

Between March and October 2021, sediment samples were collected along the stream bed in 7 points, before and after heavy rainfall events. A total of 75 sediment samples were characterised considering 9 elements concentration (i.e., Al, B, Cd, Co, Cr, Cu, Pb, Sr and Zn) of the fine sediment fraction (<63µm), total solids and volatile solids. Additionally, suspended sediment samples were taken upstream and downstream the urban area. In those two sampling points, high-resolution discharge and turbidity data were continuously monitored. Fine sediment loads were calculated in order to compute a mass balance of the urban catchment. This allowed to understand the dynamic transport mechanisms of fine sediments and relevant PBPs in the urban stream, considering complex runoff and discharge processes.

Furthermore, identification of main sources of sediments was carried out using finger-printing analysis. K-means clustering allowed to group the stream bed sediment samples into two distinct types: 1) “relatively clean sediment” and 2) “sediment affected by UWWDs”. The urban discharges increase the element concentration in the fine sediment fraction along the first 6 km of the stream. This suggests an accumulation of contaminants towards the urban gradient. However, results showed a high attenuation capacity of the urban stream, since after receiving 27 UWWDs, the elements concentration of the sediment collected in the last 1 km is statistically similar to the fine sediment collected upstream the urban area (cluster type 1).

Fine sediments export was calculated for each sewershed. Areas with UWWDs carrying high sediments and PBPs loads were distinguished. Likewise, potential hotspots of intrusion of fine sediments in the stream were clearly determined. Those hotspots could be potential locations to control fine sediments and PBPs. The findings will help prioritising and locating possible strategies to improve river water and sediment quality. 

How to cite: Rojas-Gómez, K. L., Benisch, J., Yang, S., Borchardt, D., and Krebs, P.: Accumulation of Fine Sediments and Particle-bound Pollutants in a German Urbanised Stream, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6094, https://doi.org/10.5194/egusphere-egu22-6094, 2022.

The Pb-Ag mine of Peisey-Nancroix was operated between 1734 and 1824. The associated smelters emitted Pb-rich fumes that were reported as threatening for local people all along their period of activity. Lake La Plagne is located at 2 100 m a.s.l., 7 km uphill the former mine. Considering that smelters fumes were transported uphill by prevailing winds, studying the metal contamination within Lake La Plagne sediments offers the rare opportunity to reconstruct the local atmospheric contamination, as well as the remnant catchment area contamination in a context where historical conditions of exploitation are well-constrained.

Sediments deposited before mining and smelting only contains 30 mg/kg of Pb, whereas the sediments deposited during smelting contains up to 148 mg/kg of Pb. Recent sediments deposited after mining activity period also present an enrichment in Pb (up to 58 mg/kg). Mineralogical observations (SEM-FEG) suggest that within contamination peaks, Pb is essentially associated with infra µm-scale Mn-Fe (hyrdr-)oxides.

Pb isotopes were measured on selected samples collected along the lake sediment core prior mining, during mining and smelting, and after mining. The Pb isotopic ratios of all lake sediments (n=12) indicate mixing between the isotopic ratios of the ore (n=39; galena : ²⁰⁸Pb/²⁰⁶Pb =2.092 ± 0.004 and ²⁰⁶Pb/²⁰⁷Pb= 1.173 ± 0.002), and those of the deepest lake sediments (n=2; ²⁰⁸Pb/²⁰⁶Pb =2.041 ± 0.002 and ²⁰⁶Pb/²⁰⁷Pb= 1.209 ± 0.0004) that are representative of the geochemical background. The sediments deposited long after mining still present a significant influence of local ore-derived Pb, suggesting remobilisation from the watershed of Pb inherited from the smelting period.

How to cite: Guillevic, F., Rossi, M., Arnaud, F., Poulenard, J., Quantin, C., and Monvoisin, G.: Persistent imprint of historical metallurgy in an alpine watershed evidenced from lake sediments Pb isotopes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8781, https://doi.org/10.5194/egusphere-egu22-8781, 2022.

Historically, glaciers have been seen as pristine environments. However, research has shown that glaciers can accumulate and store contaminants through processes such as atmospheric deposition, mass movements, and anthropogenic activities. Numerous anthropogenically and naturally-derived contaminants have been found within glacial sediments, including fallout radionuclides, potentially toxic elements, and heavy metals. The introduction of these contaminants often come from human activities such as the use of agricultural fertilisers, carbon based industries, vehicular use, and nuclear power plants. However, these contaminants can also originate from natural sources such as erosion of metal-rich rock and forest fires. Through mechanisms of secondary release, these often legacy contaminants are remobilized, finding their way into glacial riverine systems and downstream environments. This can then pose potential threats to human and ecosystem health, as well as impacting food quality, water resources, livelihoods, and social justice.

When assessing potential downstream risk from glacial contaminants, it is crucial to know what types of contaminants may be released in meltwaters and in what quantity. Here we identify contaminants in cryoconite – a sediment found on the surface of glaciers – in Peru’s Cordillera Blanca, from which meltwater feeds into the Rio Santa. Previous studies have shown that glaciers in similar environments (i.e. high mountain glacier catchments) have been found to contain differing types and concentrations of contaminants within cryoconite. However, until now this had not been reported for cryoconite on glaciers in Peru. This research investigates the variation in contaminant load in cryoconite from four different glaciers (Pastoruri, Shallap, Vallunaraju, and Yanapacca) within the Cordillera Blanca. Key contaminants in cryoconite from this region have been analysed using X-ray fluorescence, gamma spectrometry, and ICP-MS. These results contribute to an improved understanding of the extent to which glaciers may act as a secondary source of contaminants to the Rio Santa catchment. This is an important first step towards assessing the risk of contaminant release from glaciers in this region.

How to cite: Beard, D. B., Clason, C., Rangecroft, S., Rodríguez, W. S., and Blake, W.: Catchment scale variation of contaminants in glacial sediments from the Cordillera Blanca, Peru, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9184, https://doi.org/10.5194/egusphere-egu22-9184, 2022.

Open-channel confluences are important junctions in fluvial and artificial networks, which regulate the mixing phenomena of substances transported by the merging flows. This paper aims at contributing to the study of how the discharge ratio of the incoming flows influences the flow patterns and mixing phenomena at a T-shaped open-channel confluence with a wider downstream channel. In this study, Large Eddy Simulations (LES) are applied to compare the flow and passive scalar transport processes at two discharge ratios. The results clearly show that in the tributary-dominant case, the shear layer and the mixing interface move to the outer bank, due to the larger lateral velocities in the Confluence Hydrodynamics Zone (CHZ). Moreover, the turbulence and the secondary flow are enhanced, leading to a higher degree of mixing, as compared to the case with a dominance of the incoming flow from the main channel.

How to cite: Jin, T., Xavier Ramos, P., and De Mulder, T.: Effect of discharge ratio on flow and passive scalar transport in a T-shaped confluence with a wider downstream channel, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7821, https://doi.org/10.5194/egusphere-egu22-7821, 2022.

Turbulent flow is a chaotic condition filled with vortex structures in the flow. Based on past studies, turbulent bursting events are composed of outward interactions (Q1), ejections (Q2), inward interactions (Q3), and sweeps (Q4). Among these events, ejections (Q2) and sweeps (Q4) significantly contribute to time occupied, momentum flux, and sediment flux from the turbulent coherent structure analysis. In addition, turbulent coherent events were assumed to occur continuously in the past. However, it is noticed that, on average, approximately 90% of the total stress was found within merely 50% of the total sampling time. Furthermore, the earlier works supposed the occurrences of these events are the same, and the change between the two states is uncorrelated. It is found that the occurrences of bursting events are a non-Markovian random process. The flow region can be divided into two parts (the near-bed region and the upper layer) by the spatial gradient of the flow velocity. The flow condition near the bed bottom tends to be anisotropic because of the turbulent structures. As mentioned above, these characteristics (intermittency, memory, and anisotropy) were not considered in past studies. This study proposes a modified Stochastic Diffusion Particle Tracking Model, a stochastic Lagrangian model to describe sediment particle movement. The proposed model integrates these characteristics, such as length-scale and time-scale of coherent events determined from the Direct Numerical Simulation dataset (DNS dataset), to reveal more details of sediment particle motion in the turbulent flow. We obtain the sediment particle trajectory from the model and analyze the anomalous diffusion in sediment transport by calculating the variance of the particle trajectory. As far as we know, extreme flow events such as floods induced by typhoons or heavy rainfalls can be regarded as highly intermittency processes. When a detailed description of the turbulent flow can be made available, we can simulate sediment particle motion more comprehensively under these extreme flow conditions.

How to cite: Wu, M. J. and Tsai, C. W.: Stochastic sediment transport modeling under the effects of intermittency and anisotropy of turbulent flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7008, https://doi.org/10.5194/egusphere-egu22-7008, 2022.

Lake Onego is the second largest body of water in Europe (S lake mirrors = 9720 km², V = 295 km³, S catchment area = 53100 km²), located at the junction of two geological structures (the Fennoscandian Shield and the Russian Platform) is characterized by a complex morphology of the basin, uneven distribution of river flow and anthropogenic load.

In 2020-2021, the peculiarities of the flow of terrigenous material into the lake, affecting the formation of heterogeneity in the composition of the mineral part of the bottom sediments, were studied. New knowledge was obtained about the seasonal variability of the geochemical composition of river waters, the spatial and temporal nature of its variability was shown. By the example of iron, manganese and total phosphorus, the seasonal distribution of the forms of migration of these elements in rivers is considered. Concentrations of dissolved and suspended forms of trace elements in river waters were obtained. The uneven distribution of river suspension particles by size and degree of rolling, as well as seasonal differences in the ratio of mineral and organic components of the suspension are shown. The study of the composition of the dispersed sedimentary matter revealed similar spectra of minerals. It was found that the material of river suspensions is represented by a biogenic X-ray amorphous mass (biodetrite of diatoms, spores and pollen of plant communities) with associations of detrital mineral particles, scaly formations of layered silicates and aluminosilicates, fouling with jelly-like clots and films of oxides and hydroxides of manganese and iron on organic skeletons.

The study was supported by RFBR grant #19-05-50014, RSF research project #18-17-00176 and by the Federal Budget, within the State Assignments nos. 121021700116-6.

How to cite: Kulik, N., Efremenko, N., Belkina, N., Strakhovenko, V., and Gatalskaya, E.: Geochemical features of river flow into Lake Onego, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9411, https://doi.org/10.5194/egusphere-egu22-9411, 2022.