HS9.2

The sediments of the artificial Urft reservoir represent a unique archive of human influence on late Holocene sediment composition. The Urft dam, located in the Eifel Mountains in western Germany, was built between 1900 and 1905. At the time of its construction, the Urft reservoir was the largest reservoir and, with 12 MW, drove the most powerful water storage power plant in Europe. The reservoir has a length of 12 km and, when fully dammed, has a volume of 45.51 million m³ over an area of 2.16 km². The most important inflow is the river Urft. Today, the Urft Lake is completely enclosed by the Eifel National Park.

Consequently, sediments were deposited in the lake almost undisturbed over the last 115 years. Due to construction work on the Urft dam and the inspection of the 2.7 km long Kermeter Tunnel, which powers the Heimbach hydroelectric power plant, the reservoir was almost completely drained in November 2020. This offered the rare opportunity to sample the deposits in detail and to record the entire lake area photogrammetrically using an Unmanned Aircraft System (UAS). The work was carried out in cooperation between the Water Board Eifel-Rur (WVER) and the Chair of Physical Geography and Geoecology (PGG) at RWTH Aachen University.

Within the framework of the project, the sediments in the reservoir will be investigated in detail. The comparison of the high-resolution UAS digital elevation models and historical maps will give insights in the amount of sediment deposition in the different areas of the lake during the last 115 years. Geochemical markers will be used to quantify the anthropogenic influence on the sediments in the form of mining-induced pollutant contamination (e.g., heavy metals) and to relate this to the history of use in the catchment area. Another focus will be on recording the microplastics content of the different sediment layers. Since microplastics have only been introduced into the natural system by humans for the last 70 years since the beginning of mass production around 1950, the sediment layers can also be differentiated in terms of time. For these investigations, a total of ten sediment cores with a length of up to 4 m were taken from the deposits.

How to cite: Stauch, G., Esch, A., Dörwald, L., Esser, V., Lechthaler, S., Lehmkuhl, F., Schulte, P., and Walk, J.: 115 years of sediment deposition in the Urft reservoir (Eifel Mountains, western Germany), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-148, https://doi.org/10.5194/egusphere-egu21-148, 2021.

Acid mine drainage (AMD) threaten ecosystems world-wide and research on biological remediation techniques are increasing. One of them is bacterial sulfate reduction (BSR) that immobilizes the aqueous sulfate and through coprecipitation removes dissolved metals from the more bioavailable phase. Although BSR has previously only been investigated at the local wastewater treatment scale (e.g. for constructed wetlands), it is unknown to which extent they contribute to contaminant attenuation at larger scales (e.g. a hydrological basin). We developed a new method to trace the activity of BSR within an AMD-impacted catchment using sulfur isotopes (δ³⁴S) and found that they naturally reduce 30% of the riverine sulfate and metal concentrations, with a spread from 10 to 50% reduction within the catchment. These results are based on surface water field measurements from our test site in northern Sweden combined in a mass-balance mixing model where we explicitly addressed the isotopic fractionation from bacterial activity. This innovative mapping of catchment-scale biogeochemical natural attenuation provides important clues to strategically target remediation measures, e.g. potential in-situ enhancement of the BSR activity. In combination with stable water isotopes we hope to refine this method to further identify BSR hot spots within the catchment and to extend its application to other sites, e.g. the Khibiny mining region, Russia.

How to cite: Fischer, S., Jarsjö, J., Rosqvist, G., and Mörth, C.-M.: Catchment-scale metal retention revealed from natural bacterial sulfate reduction (BSR), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8238, https://doi.org/10.5194/egusphere-egu21-8238, 2021.

The intensive farmland in north China accounts for more than 17% of China's arable land area and is main producing area of wheat and corn in China. The response of sources and loads of sediment of N and P pollutants to the high-intensity agricultural activities in north China still remains unclear. The study aims to quantify the source and magnitude of N and P pollutants in the sediment from different land use types using a novel application of compound-specific δ¹³C isotopes (CSSI), ¹³⁷Cs and ²¹⁰Pb_ex (FRNs), in a representative agricultural catchment (Jiangou). Surface (0-2 cm) soil and sediment samples were collected from different plant species for CSSI and FRNs, while subsurface (5-30 cm) soil samples were collected from channel bank for FRNs. The ¹³⁷Cs cores (0-60 cm) collected at the outlet of the catchment and also at reference sites. Sediment sources from surface and subsurface soils were derived by FRNs data which accounted by 83±6% and 17±6%, respectively, while the sediment sources from maize, bean, vegetable farmlands and forestlands on the surface soil areas were identified by CSSI data. Combining FRNs and CSSI fingerprinting techniques, the dominant sediment source was derived from maize farmland which contributed by 60±8%, followed by channel bank, bean farmland and vegetable farmland which accounted for 17±6%, 12±3% and 8±3%, respectively, and the least contribution was from forestland (3±1%). According to the ¹³⁷Cs cores (0-60 cm) collected at the outlet of Jiangou catchment, a sedimentation rate of 23.38±0.22 t ha^-1 yr^-1 of this study catchment was quantified. The ¹³⁷Cs inventory of the reference site was 1162±131Bq m^-2. Based on the measured of N and P concentrations in source samples, and areas of land uses in this catchment, we quantitatively estimated the N pollutant in sediment (t yr^-1) from maize (2.19), bean (0.42), vegetable farmlands (0.31), forestland (0.49) and channel bank (0.05), while P pollutant (t yr^-1) were 4.39 for maize, 0.18 for beans, 0.28 for vegetable farmland, 0.37 for forestland and 0.04 for channel bank. This study shows that the novel conjunctive use of FRNs and CSSI techniques could quantify the N and P pollutants in sediment from different land uses in catchment, which is critical to assess and implement effective agricultural and land management practices.

How to cite: Yu, H. and Adu-Gyamfi, J.: Quantitively and novelty source fingerprinting N and P pollutants in sediment: Case study in a small catchment, North China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10946, https://doi.org/10.5194/egusphere-egu21-10946, 2021.

The Mediterranean area hosts three important mercury mining districts, which are presently abandoned and partially reclaimed: Almadén (Spain), Monte Amiata-Abbadia San Salvatore (Italy) and Idrija (Slovenia). The Galleria Italia (Italy) is the only mining drainage of the former mining area from Abbadia San Salvatore, which feeds the 2.5 km long Fosso della Chiusa. The Galleria Italia waters are circumneutral (pH ≈ 6) and characterized by Ca(Mg)-SO₄ composition; TDS around 1000 mg/L; high concentrations of Fe, Mn and Al (18714.5, 493.3, 486.6 μg/L, respectively) and dissolved CO₂. The high content of these elements is also present in the stream sediments. In the mining district area of Abbadia San Salvatore, the Galleria Italia-Fosso della Chiusa system is connected to a major riverine network: i.e. the Pagliola, Paglia and Tiber rivers. This work is aimed to (i) characterize the interaction of Hg and As between the water and sediment compartments in the Fosso della Chiusa by including the suspended particulate; (ii) estimate the total Hg and As mass load released by Galleria Italia and iii) evaluate the total load discharged in the riverine network from the circumneutral mine drainage using the Igeo index. In 2020, during four sampling sessions, waters, sediments and suspended particulate were collected all along the Fosso della Chiusa creek. Each sampling station was located maintaining a relatively equidistance from the source to the confluence with the Pagliola river. Specific aliquots at 13 sites were collected to geochemically characterize the creek waters. Also, stream sediments were collected for determining the mineral composition and As, Hg, Sb while at the source and the mouth  2 L of waters were filtered at  <0.45 μm to measure the suspended material and the concentration of three chalcophile elements. A general decrease of the As content was observed along the creek in both waters and sediments, i.e. from 336 to 2 mg/kg and from 12 to 0.3 μg/L, respectively whereas no a clear trend was recognized for Hg, where the higher contents being up to 105 mg/kg and 2.8 μg/L, respectively. It is to mention that the reddish-whitish colour of the waters and sediments (due to the presence of oxy-hydroxide of Fe and, subordinately, Al and Mn) decreasing down to about 1 km from the source, suggesting, as supported by the analytical data, that the presence of the toxic elements in both the solid and aqueous phase. This implies that the environmental impact by the Galleria Italia waters and related sediments is limited spatially at least for As, as also evidenced by the Igeo index applied to sediments for As and Hg, the former showing a general decrease from Class 6 ( “extremely contaminated’’) to 1 (‘’non to moderately contaminated’’). Differently, Hg in each sampling site belongs to Class 6. Nevertheless, the Igeo ranking suggests that As tends to be preferentially partitioned in the liquid phase whilst Hg is mainly enriched in the solid fraction. This contrasting behaviour of As and Hg is also analytically observed when the suspended particulate is considered.

How to cite: Lazzaroni, M., Zuccolini, M., Nisi, B., Cabassi, J., Rappuoli, D., and Vaselli, O.: Mercury and arsenic in suspended particulate and sediments from the Fosso della Chiusa creek fed by the Galleria Italia mining drainage (Abbadia San Salvatore, central Italy)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12239, https://doi.org/10.5194/egusphere-egu21-12239, 2021.

After approximately two decades of plastic research in freshwater environments, plastics and especially microplastics (d < 5 mm) have entered the scientific consciousness as an anthropogenic pollutant. Even if this pollutant shows certain comparability with heavy metal pollution in soils and sediments, it should be seen as a purely anthropogenic material without geochemical or natural background loads, which leads to the assumption that it might also be a potential marker of the Anthropocene. Regarding the global plastic cycle within the environment, rivers act as main transport paths from land-to-sea. As rivers are embedded into landscapes, accumulation of plastics within riverine (e.g. sediment temporary sink) and accompanied terrestrial environments (e.g., floodplain storage for deposited plastics) has been proven in initial studies.

In contrast to other natural or anthropogenic pollutants, the approximate time since plastics and microplastic can be introduced into the environment starts in the 1950's with increasing global plastic production and consumption. A steady increase of possible plastic loads with the rising plastic production, probably decreasing with beginning environmental responsibility (approx. 2010 or beyond) leads to the fact, that plastic contents mainly occur in sediments and soils over a period of the last 70 years. This circumstance in connection with the general known sink function of soils and sediments, especially floodplains, nutrients as well as pollutants, allows the consideration of plastic deposits for dating purposes. As different dating methods reach their limits regarding comparatively young sediments, the connection between plastic deposition depth and temporal entry provides a basis for dating recent sediment layers. Possible detailed age differentiations in dependence on the identification of polymer types and additives, particle surface appearance (e.g., fresh/weathered) or spectroscopic criteria (e.g., surface weathering determination) are thinkable.

The opinion presented here, aims to address this new opportunity on the basis of own research findings within floodplains as well as other studies and highlights two main requirements: The first requirement for a sufficient dating implementation of plastic particles is the particle size: Detection and application for dating purposes is relatively easy to apply for macro- and mesoplastic particles (˃5 mm), due to size and less mobility in soils or sediments (e.g., plastic films embedded in sediment structure). In contrast for particles in the microplastic size class (˂ 5mm down to 1 µm) we recommend only the consideration of coarse microplastics (˃ 2mm) as smaller particles could easily shift in soils and sediments (e.g., bioturbation, preferential flow).  Additionally, the selection of a suitable sampling site as a second requirement depends on the appropriate localization within the floodplain area and surface morphology, sampling depth, flood history and anthropogenic influences.

Apart from the numerous potential environmental risks of plastics, their purely anthropogenic production and their respectively features, can turn them into a useful dating tool in river and floodplain sediments and thus enabling, besides the detection alone, a further application. This approach could also be transferred to marine or lacustrine sediments in future.

How to cite: Weber, C. J., Lechthaler, S., Stauch, G., and Opp, C.: Plastics and microplastics – A future marker to reconstruct floodplain chronology (Opinion), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-62, https://doi.org/10.5194/egusphere-egu21-62, 2021.

Mar Menor (SE, Spain) is one of the largest coastal lagoons in the Mediterranean basin. Its ecological and economic significance has led to its inclusion in several protection programmes, both on a national and international level. In the last decades, this semiconfined habitat has been under high anthropogenic pressure from agricultural, mining and tourism activities, which have resulted in significant changes, such as eutrophic events and their cascading ecological effects. Previous research suggests that this degradation is linked to the introduction of nutrients and contaminants to this ecosystem, which are accumulated in the sediments of the lagoon. In this work, sediment cores from key locations of the Mar Menor were collected in order to estimate the amount of accumulated chemical compounds, such as metals and organic compounds. The results of this study are used to reconstruct the historical record of contaminants, which can fuel future contamination episodes in the lagoon.  

How to cite: Alorda-Montiel, I., Rodríguez-Puig, J., Alorda-Kleinglass, A., Diego-Feliu, M., Rodellas, V., and Garcia-Orellana, J.: Historical record and sources of contaminants in sediments from Mar Menor coastal lagoon., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15883, https://doi.org/10.5194/egusphere-egu21-15883, 2021.

During heavy rainfall events, the large amounts of generated runoff in urban areas mobilise particulate matter from different surfaces. These particles have attached other contaminants such as heavy metals, polycyclic aromatic hydrocarbons and, faecal microorganisms. In urbanised areas, particle-bound contaminants (PBCs) may reach rivers through surface runoff, combined sewer overflows or storm water discharges. This may affect the water quality of receiving water bodies and creates health risks to humans and ecosystems. Due to the spatial variability of PBCs, associated to different land uses and pollution sources, the quantification and characterisation of contaminant pathways remain a challenge. Despite high investments, the implemented management alternatives to improve river water quality are still inefficient due to late identification of pressures and lack of a real paradigm shift towards holistic approaches. Therefore, it is necessary to better understand and describe the main factors controlling PBCs pathways in urban areas. This is expected to facilitate the selection of appropriate technologies and strategies to reduce the impact of urban discharges on receiving water bodies.

In this context, the aim of this study is to evaluate the influence of spatial and temporal variability of sediments and PBCs sources on river water quality in an urbanised catchment, considering land-use distribution within the sewersheds. This is expected to provide a better understanding of the relationship between drivers of relevant PBCs and the response of the urban water system under dynamic conditions (i.e. variable sediment load, urban runoff, storm water discharge and river flow). 

Data for this study is obtained from an integrated monitoring network in a small watershed (Lockwitzbach) located in Dresden, Germany. This urban observatory consists of four water quality monitoring stations within the stream and in the sewer network. High-resolution (1min) discharge and turbidity data are collected. This allows to understand the dynamic transport mechanisms of sediments in the catchment, providing insights in complex runoff and discharge processes.

Integrated simulation of sediments and PBCs (i.e. heavy metals) is done by using EPA SWMM to evaluate surface build-up and wash-off. Additionally, the impact of sedimentation, accumulation and re-suspension of sediments and heavy metals within the sewer network and river are analysed using a simplified block developed in Simba#. Calibration and validation of the integrated model was done using online monitoring data and water samples taken during the period 2018-2020. Turbidity was used as a proxy for total suspended solids and PBCs. We identified and prioritised urban areas that are hotspots for high sediment and PBCs loads. Those represent potential locations for an optimal control and reduction of water pollution strategies. Results suggest that integrated simulation is an effective approach to analyse transport mechanisms and pathways of sediments and PBCs within urbanised catchments. Furthermore, high-resolution discharge and turbidity data are especially useful to represent the wash-off of contaminants associated to the first flush process during rainfall events.

How to cite: Rojas-Gómez, K. L., Benisch, J., Reyes-Silva, J. D., Mariano, R., Yang, S., Helm, B., Borchardt, D., and Krebs, P.: Integrated Simulation of Particle-Bound Contaminants in Urbanised Catchments Using High-Resolution Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3232, https://doi.org/10.5194/egusphere-egu21-3232, 2021.

Water and sediment are the main transport materials transported by rivers to the ocean, playing a crucial role in the evolution of river-delta-estuary-coast topography. Strong anthropogenic activities and climate change have led to distinct hydrological changes and geomorphological responses in river systems worldwide. However, previous studies usually considered the changes of streamflow and sediment load and the evolution of river channel and delta separately, and the understanding of the interactions between hydrological changes and geomorphological responses from the perspective of basin system integrity remains limited. In this study, using the Mann-Kendall trend test, normalized anomalies analyses and sediment budget analyses, the basin-wide streamflow and sediment load changes stretching from the headwater to the delta in the Yellow River basin (YRB) during 1956-2019 were examined, and the coupling relationships of water-sediment variations with channel erosion and delta evolution across the basin were explored. The results indicate that the streamflow and sediment load in the YRB decreased significantly over the past six decades except the headwater, and the decrease rate increased along the downstream continuum with the whole basin. However, the streamflow increased significantly and the sediment load tended to be gradually stabilizing since 2000. The reduction of sediment load mainly occurred in the middle-lower river downstream. The sediment yield coefficient in the middle reach decreased linearly with the reservoir capacity and exponentially with the vegetation coverage and number of check dams (p < 0.01), and the sediment reduction rate increased exponentially with the increase of terraces proportion, and gradually approached the limit value of 96.20% (p < 0.01). The ratio of sediment load at the outlet of the upper reach over that exporting from the middle reach was stable before 2000, but it increased and fluctuated sharply after 2000 as a result of ecological restoration campaign in the middle reach. The sediment load at the outlet of the middle basin was about 1.99 times of that transporting to the ocean before 2002, but their ratio decreased to be 0.69 after 2002 due to the operation of water-sediment regulation project. The construction of reservoirs gradually reduced the erosion in the headwater to near zero, and the river sediment deposition in the middle reach increased linearly with the reservoir capacity, whereas the sediment deposition in the lower reach depended on the sediment concentration exporting from the middle reach. The decreasing sediment supply also resulted in the gradual erosion of delta land since 2000 with combination of tidal waves. This study provides a synthesis of the relationships among water, sediment, channel and delta from the entire river system in the YRB, and it can shed light on integrated basin management adapting to anthropogenic activities and climate change.

How to cite: Yin, S., Gao, G., and Fu, B.: Interactions between hydrological changes and geomorphological responses in the Yellow River basin from the perspective of basin system integrity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4661, https://doi.org/10.5194/egusphere-egu21-4661, 2021.

River inflows have a major influence on lake water quality through their input of sediments, nutrients and contaminants. It is therefore essential to determine their pathways, their mixing with ambient waters and the amount and type of Suspended Particulate Matter (SPM) they carry. Two field campaigns during the stratified period took place in Lake Geneva, Switzerland, in the vicinity of the Rhône River plume, at high and intermediate river discharge. Currents, water and sediment fluxes, temperature, turbidity and particle size distribution were measured along three circular transects located at 400, 800 and 1500 m in front of the river mouth. During the surveys, the lake was thermally stratified, the negatively buoyant Rhône River plume plunged and intruded into the metalimnion as an interflow and flowed out in the streamwise direction. Along the pathway, interflow core velocities, SPM concentrations and volumes of particles progressively decreased with the distance from the mouth (by 2-3 times), while interflow cross sections and plume volume increased by 2-3 times due to entrainment of ambient water. The characteristics of the river outflow determined the characteristics of the interflows: i.e. interflow fluxes and concentrations were the highest at high discharge. Both sediment settling and interflow dilution contributed to the observed decrease of sediment discharge with distance from the mouth. The particle size distribution of the interflow was dominated by fine particles (<32 μm), which were transported up to 1500 m away from the mouth and most likely beyond, while large particles (>62 μm) have almost completely settled out before reaching 1500 m. 

How to cite: Piton, V., Soulignac, F., Lemmin, U., Benjamin, G., Wynn, H. K., and Barry, A.: Nearfield development of the negatively buoyant Rhône River inflow into Lake Geneva as an interflow: suspended particulate matter and associated fluxes., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8890, https://doi.org/10.5194/egusphere-egu21-8890, 2021.

In an ongoing study to the decline in suspended sediment concentrations and loads in the Rhine river since the mid-1950s, the temporal changes in the power-law sediment rating curve parameters were examined. This revealed that the rating exponent of the rating curve increased substantially between the early and late 1980s. Until the early 1980s, the ratings curves were relatively flat with values of the rating exponent b varying around 0.2. In the mid-1980s, the exponent suddenly increased to a value between 0.4 and 0.6 and since then has remained within this range. This change in the rating exponent was mainly caused by a decrease in suspended sediment concentrations during low discharges. During high discharges, the suspended sediment concentration initially increased during the late 1980s, but this increase was nullified soon afterwards due to the declining trend in suspended sediment concentration.

The sudden increase of the rating exponent coincided with the period that the Ponto-Caspian Chelicorophium curvispinum (Caspian mud shrimp) invaded the Rhine river basin. This suggests that this suspension-feeder species bears the prime responsibility for this increase, although this hypothesis requires further independent evidence. The sudden increase in the rating exponent does however not manifest itself in the long-term gradual trend of declining suspended sediment concentrations and vice versa. Apparently, the sequestration of sediment by Chelicorophium curvispinum is only temporary: the suspended sediment sequestered during periods of relatively low discharges is likely remobilised again during periods of high discharge. This implies that the invasion of Chelicorophium curvispinum has not played a significant role in the decline of suspended sediment concentrations. The precise reasons for the gradual long-term decline in suspended sediment concentration remain yet unknown.

How to cite: van der Perk, M.: Impact of Chelicorophium curvispinum on the concentration-discharge response of suspended sediment in the Rhine River, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9199, https://doi.org/10.5194/egusphere-egu21-9199, 2021.

Agricultural land is a key source of fine sediment and nutrients, often contributing significantly to diffuse pollution and catchment water quality issues. In the UK, recent efforts to mitigate agricultural diffuse pollution and reverse declines in the chemical and ecological status of waterbodies have focussed on catchment-based approaches. These nature-based solutions involve restoring, enhancing, or emulating natural processes to slow, store, and filter water and contaminants as they move through a catchment. Several studies in UK catchments show the potential benefits of retention ponds and constructed wetlands, however their functioning has been shown to vary according to their design and the catchment typology they are situated within.

To help further the evidence base on the effectiveness of ponds for mitigating diffuse agricultural pollution, we monitored a series of small, connected pond features (draining 0.3 km² of slowly permeable clay soils) created as part of the Littlestock Brook Natural Flood Management (NFM) scheme. This lowland NFM scheme, situated in the headwaters of the River Thames basin (South East England), targets the issues of flooding and diffuse pollution, and is delivered through the Evenlode Catchment Partnership and Environment Agency as part of a five-year project (2016-2021).

Water and sediment sampling were undertaken during both baseflows and stormflows to determine retention of sediment and phosphorus species within the ponds under varying hydrological conditions. Results demonstrate that during small to moderate storm events, the ponds were able to capture run-off and reduce peak concentrations of suspended solids and particulate phosphorus. However, during large magnitude events, the ponds became inundated and resuspension of previously deposited sediment caused a net loss of material from the system. We estimate that the annual settling flux within the pond series is 16.48 tonnes (±5.77) for sediment, and ~0.014 tonnes for phosphorus. This equates to 17% (±6) of the annual suspended sediment load for the wider 3.4 km² sub-catchment area. This study highlights the complexities of sediment dynamics in connected pond features and the importance of maintenance for retention efficiency.

How to cite: Robotham, J., Old, G., Rameshwaran, P., Sear, D., Gasca-Tucker, D., Soteriou, H., Bishop, J., Berkeley, A., McKnight, D., and Old, J.: Monitoring the effectiveness of connected ponds at fine sediment and phosphorus retention in a lowland agricultural stream, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7370, https://doi.org/10.5194/egusphere-egu21-7370, 2021.