The transfer of sediments and associated contaminants play an important role in catchment ecosystems as they directly influence water quality, habitat conditions and biogeochemical cycles. Contaminants may include heavy metals, pesticides, nutrients, radionuclides, and various organic, as well as organometallic compounds. The environmental risk posed by sediment-bound contaminants is largely determined by the sources and rate at which sediments are delivered to surface water bodies, the residence time in catchments, lakes and river systems as well as biogeochemical transformation processes. However, the dynamics of sediment and contaminant redistribution is highly variable in space and time due to the complex non-linear processes involved. This session thus focuses on sources, transport pathways, storage and re-mobilization, and travel times of sediments and contaminants across temporal and spatial scales as well as their impact on catchment and freshwater ecosystems.

This session particularly addresses the following issues:
- Delivery rates of sediments and contaminants from various sources (i.e. agriculture, urban areas, mining, industry or natural areas);
- Transport, retention and remobilization of sediments and contaminants in catchments and river reaches;
- Modelling of sediment and contaminant transport on various temporal and spatial scales;
- Biogeochemical controls on contaminant transport and transformation;
- Studies on sedimentary processes and morphodynamics, particularly sediment budgets;
- Linkages between catchment systems and lakes, including reservoirs;
- Analysis of sediment archives to appraise landscape scale variations in sediment and contaminant yield over medium to long time-scales;
- Impacts of sediments and contaminants on floodplain, riparian, hyporheic and other in-stream ecosystems;
- Response of sediment and contaminant dynamics in catchments, lakes and rivers to changing boundary conditions and human actions.

Co-organized by GM3
Convener: Núria Martínez-Carreras | Co-conveners: Patrick Byrne, Marcel van der Perk, Ottavia ZoboliECSECS
vPICO presentations
| Mon, 26 Apr, 09:00–10:30 (CEST)

Session assets

Session materials

vPICO presentations: Mon, 26 Apr

Chairpersons: Marcel van der Perk, Ottavia Zoboli, Patrick Byrne
10-minute solicited presentation
Georg Stauch, Alexander Esch, Lukas Dörwald, Verena Esser, Simone Lechthaler, Frank Lehmkuhl, Philipp Schulte, and Janek Walk

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.

2-minute presentations
Virginia Panizzo, Lucy Roberts, Nga Do, Sarah Taylor, Michael Watts, Elliott Hamilton, Suzanne McGowan, Duc Trinh, Melanie Leng, and Jorge Salgado

Suspended particulate matter (SPM) in large rivers is the main source of material into delta river ecosystems and the world’s oceans, and is the primary carrier of heavy metals. Large rivers are therefore important sources of pollutant transport through the watershed and potentially alter natural riverine biogeochemical cycling. Asian mega-deltas are some of the most densely populated and urbanizing environments in the world, with pollution, erosion, and anthropogenic catchment modifications changing sediment fluxes and pollutant transport across their catchments. The River Delta (RRD), northern Vietnam, comprises 14,300 km2, making it the fourth largest delta in Southeast Asia. The area has a large population of >22 million and has seen a rapid increase in industry and agriculture with waste products from domestic activities, agriculture, and industry entering the river network often unregulated and untreated. To estimate the impacts of industrialisation in the RRD delta, we measured downriver suspended sediment and pollutant flux from 21 locations over a 17 month period from March 2018 to July 2019. Previous studies suggest sediment retention in the RRD, which is supported here in 2019 with ~30% of sediments retained in the delta. Increased precipitation in 2018, however, led to a ~40% increase in sediment delivery between the inlet and the outlets of the delta, most likely attributed to erosion. Anthropogenic contaminant loads between the inlet and outlets suggest the retention of heavy metals within the delta irrespective of the sediment flux (e.g. a reduction by ~4 and ~14% of SPM bound Cr between sites in 2018 and 2019). This may, in part, be due to spatial variations across the delta revealing ‘hotspots’ of pollution, with a progressive increase in the Cr concentration of SPM between Son Tay (a predominantly agricultural landscape) and Hanoi (a major industrialised urban area) suggesting domestic and industrial waste are major sources of heavy metal pollution. XRF data from upstream Hoa Binh reservoir sediment cores (collected 2017) will permit a comparison of background contaminant storage in the RRD catchment, to better quantify downstream impacts of anthropogenic activity as well as underpin the effects of impoundments on sediment export from the riverine system. Results highlight the role of deltas in ‘filtering’ contaminants to protect coastal areas, but the retention of high loads of pollutants also has potential consequences for the bioaccumulation of heavy metals through the food chain and could ultimately have severe consequences for aquatic and human health in these areas. 

How to cite: Panizzo, V., Roberts, L., Do, N., Taylor, S., Watts, M., Hamilton, E., McGowan, S., Trinh, D., Leng, M., and Salgado, J.: Transport and storage of anthropogenic contaminants in the Red River Delta, Vietnam , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15360, https://doi.org/10.5194/egusphere-egu21-15360, 2021.

Ngoc Diep Nguyen, Malgorzata Grybos, Marion Rabiet, and Véronique Deluchat

The hydrodynamics of dam reservoirs favor the accumulation of phosphorus (P) in bottom sediments since it has a strong affinity for the sedimentary particles. However mechanical disturbance of sediment (resuspension) may release P back to water column. The load of sedimentary P poses a serious ecological problem related to the maintaining of water eutrophication. The aim of this study was to evaluate the potential of sediments, accumulated in Champsanglard reservoir (Central France), to release water-mobilizable colloidal and dissolved P. A sampling campaign was carried out at different locations along the main channel of reservoir from riverine to lacustrine area and characterized by different hydrodynamics. The results showed that colloids are intrinsic component of reservoir sediment and contribute up to 2.3% of sediment mass. Colloidal P attributed up to 6% of total sedimentary P and 80% of water-mobilizable P (fraction < 1 µm). The stock of water-mobilizable colloids and associated P varied according to particle size distribution and was strongly dependent to channel morphology, hydrodynamics and inlet of tributary.

Keywords: Dam reservoir, sedimentary colloids, phosphorus form, spatial variability

How to cite: Nguyen, N. D., Grybos, M., Rabiet, M., and Deluchat, V.: Spatial distribution of water-mobilizable colloids and phosphorus from dam reservoir sediment , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15545, https://doi.org/10.5194/egusphere-egu21-15545, 2021.

Jessica Ponting, Anne Verhoef, Michael Watts, and Tom Sizmur

Climate projections suggest that rainfall events will become more frequent and intense, which may lead to more widespread flooding. Floodplains can be used to help reduce the magnitude of floods downstream by storing excess flood water, thus making them useful for flood risk management. This means that floodplains are subjected to repeated drying and rewetting, which has implications for biogeochemical cycling of chemical elements in floodplain soils.

Floodplains have been considered a sink for contaminants in urban catchments, where high river flows transport contaminated sediments downstream and deposit them onto the floodplain topsoil. With increasing flooding frequency and duration, floodplains may become sources of legacy pollution through desorption of contaminants into soil porewater or resuspension of particulate matter into the overlying floodwater. Therefore, flooding could re-mobilise potentially toxic elements (PTEs) such as Cadmium (Cd), Copper (Cu), Chromium (Cr), Nickel (Ni), and Lead (Pb) that are present in the floodplain soil as a result of historic deposition. Mobilising PTEs in floodplain soils may cause adverse ecological impacts for soil microorganisms, plants, and both terrestrial and aquatic fauna.

The mobility of PTEs from the floodplain soil can increase or decrease due to the net effect of five key processes that influence dispersion and accumulation; 1) soil redox potential for which decreases  can directly alter the speciation, and hence mobility, of redox sensitive PTEs (e.g. As and Cr), 2) soil pH for which an increase usually reduces the mobility of metal cations (e.g. Cd2+, Cu2+, Ni2+, Pb2+), 3) dissolved organic matter which can mobilise PTEs were strongly bound to soil particles, 4) iron (Fe) and manganese (Mn) hydroxides undergo reductive dissolution, releasing adsorbed and co-precipitated PTEs, and 5) reduction of sulphate which immobilises PTEs due to precipitation of metal sulphides.

We took a field-based approach; extracting soil pore waters from a floodplain downstream of a typical urban catchment in southeast England before, during and after a flooding event. During the flood, there was increased mobility of Cd and Pb, and decreased mobility for Cu and Cr, compared to the mobility before flooding. After the flood, Ni mobility increased, whereas the other PTEs had lower mobility than they had prior to the flood. We also measured explanatory variables (e.g. pH, redox, Fe and Mn) that might explain the changes in mobility of PTEs that we found. Reductive dissolution of Mn is a possible mechanism for the increased mobility of Cd and Pb and redox likely played a role in the reduced Cr mobility.

Flooding did not influence the mobility of all PTEs in the same way. The duration of flooding is thought to influence the mobilisation due to the length of time for key processes to take place. It is therefore difficult to predict what PTEs might be mobilised into the environment with any given flooding event, further work is required to identify which soil properties should be measured in order to improve our capability to predict how a flooding event will influence the mobility of individual PTEs in geochemically contrasting floodplain soils.

How to cite: Ponting, J., Verhoef, A., Watts, M., and Sizmur, T.: Impact of fluvial flooding on potentially toxic element mobility in floodplain soils , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6260, https://doi.org/10.5194/egusphere-egu21-6260, 2021.

Luisa Helm, Fabienne Uphoff, Piero Bellanova, Nina Engels, Jan Schwarzbauer, Frank Lehmkuhl, and Klaus Reicherter

An alarming rise of sea level is the most prominent but by far not the only hazardous phenomenon caused by climatic change. Extreme weather events with increasing frequency, such as droughts or contrasting heavy rainfalls, cause severe harm to local populations. This holds true especially for fast-growing urban centers, such as Chennai (India) with a missing or unmaintained waste and drainage management. These large coastal population centers face an increasing vulnerability to frequently reoccurring monsoon-induced floods (e.g., Chennai flood 2015; Kochi flood 2018, 2019), intensified by the advancing urbanization along the urban landscape crossing river systems and adjacent floodplains. Accompanied with these extreme floods are the increased release, re-localization and distribution of toxic xenobiotics and other pollutants (e.g., PAHs, LABs, DEHA, Mesamoll®, NBFA, and pesticides) causing harm to adjacent communities and the environment along the river’s pathway. In order to endeavor the unknown risk posed by toxic river floods, to assess the flood and associated pollution history the preserved pollution signature from sedimentary records needs to be considered.

This investigation evaluates the inorganic and organic pollutant assemblage in nine sediment profiles along the Adyar and Cooum rivers (Chennai, India). Thereby heavy metals (Cr, Ni, Cu, Zn, Pb) show a continuous concentration decrease downstream towards the coast with their specific sources remaining unsolved. Based on GC-MS analysis, four main groups of organic pollutants have been detected: petrogenic pollutants (hopanes, PAHs), urban wastewater compounds (LABs, DEHA, methyl-triclosan, octocrylene), technical compounds (Mesamoll®, DPE, NBFA, PCBs) and pesticides (DDX). Organic compounds show a distinctly differing distribution pattern compared to the heavy metals. Some compounds (e.g., PAHs, LABs, DEHA, NBFA, Mesamoll®) were detected in high concentrations deriving from nearby point sources (e.g., tributaries, canals). While most organic compounds show high source specific properties, the definite sources for other compounds remain vague as the result of large scale and diffusiveness of anthropogenic emissions, such as air pollution or (untreated) industrial and municipal wastewaters. The chosen approaches have shown that urban wastewater pollutants and several technical compounds are suitable markers to assess the anthropogenic induced pollution and event history in sedimentary archives. However, the given sedimentary archives in these fast-growing and urbanized population centers might not always allow a full reconstruction of past events, as anthropogenic alterations on the rivers course and floodplains effect the archive’s preservation potential. For Chennai, advantages and disadvantages regarding the chemostratigraphic preservation are delicately balanced. However, increasing urbanization and anthropogenic overprinting causes the disruption of sedimentary archives and redistribution of contaminated material (e.g., through dredging), this favors remobilization and relocation of hazardous contaminants, thus endangering the local population due to the high mobility of these pollutants.

How to cite: Helm, L., Uphoff, F., Bellanova, P., Engels, N., Schwarzbauer, J., Lehmkuhl, F., and Reicherter, K.: Remobilization of hazardous contaminants caused by climate-induced flood events in (sub-)tropical river systems (Chennai, India), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14389, https://doi.org/10.5194/egusphere-egu21-14389, 2021.

Hung-Chun Chao

    Sediment geochemistry has been widely used to indentify the source of the sediments delivered from catchment to the deposition basin.  In this study, bed load sediments, high terrace soils, beach sediments, and cores drilled at estuary were collected at the catchment of Gangkou River and its tributary, Linlu River, southern Taiwan.  All sediments were sieved by 0.062 μm sifter and exchangeable, carbonate, and iron oxide phases were leached and only residue silicate phase were digested.  Chemical composition, rare earth elements (REEs), and lead isotopes were measured.  The results show that two major catchments, Linlu River and Gangkou River, as well as high terrace soil and beach sediments can be successfully classified by chemical composition and lead isotopes.  However, REEs show signature of upper continental crust and no differences among all the samples, possibly due to the same source of high REEs minerals.  The characteristic of chemical composition and lead isotopes are different between two catchments and the estuary sediments as well as beach sediments near the estuary imply mixing behavior between two catchments.  The upper most of the estuary core samples, presented as modern sediment, have similar chemical composition and lead isotopes compared with the mainstream.  However, the beach sediment on the top of the dune and the lower part of the core samples, which are elder than 7 ka, have distinct chemical and isotopic characteristics, indicating different sediment sources.  In, summary, chemical composition and the lead isotopes are robust tracers for the leached fine sediments in Gangkou River catchment but REEs are not.  The results of estuary core indicate that the sediment source of the estuary before 7 ka is different from the present.

How to cite: Chao, H.-C.: Spatial distribution of the sediments in the Gangkou River catchment: Evidence from chemical composition, rare earth elements, and lead isotopes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-483, https://doi.org/10.5194/egusphere-egu21-483, 2021.

Sandra Fischer, Jerker Jarsjö, Gunhild Rosqvist, and Carl-Magnus Mörth

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.

Hanqing Yu and Joseph Adu-Gyamfi

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 210Pbex (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.

Marta Lazzaroni, Marino Zuccolini, Barbara Nisi, Jacopo Cabassi, Daniele Rappuoli, and Orlando Vaselli

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.

Collin J. Weber, Simone Lechthaler, Georg Stauch, and Christian Opp

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.

Irene Alorda-Montiel, Júlia Rodríguez-Puig, Aaron Alorda-Kleinglass, Marc Diego-Feliu, Valentí Rodellas, and Jordi Garcia-Orellana

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.

Karen L. Rojas-Gómez, Jakob Benisch, Julian D. Reyes-Silva, Renato Mariano, Soohyun Yang, Björn Helm, Dietrich Borchardt, and Peter Krebs

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.

Shihua Yin, Guangyao Gao, and Bojie Fu

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.

François Mettra, Koen Blanckaert, Ulrich Lemmin, and David Andrew Barry

In Lake Geneva, a deep peri-Alpine lake in Switzerland, the sublacustrine Rhône River delta presents a deep canyon, the Rhône Canyon. Previous studies and recent observations show that low-velocity underflows and high-velocity turbidity currents pass frequently in the Rhône Canyon. The former carry little sediment, are long-lasting, slow moving and typically occur in winter when the lake is destratified, whereas the latter are sediment-rich, short-lived and occasionally generate high velocities. In the present study, we revisit three different event types that can trigger turbidity currents in the Rhône Canyon: large-scale floods of the Rhône River, sublacustrine slides on the Rhône delta and short high concentration sediment transport events induced by localized severe storms in the Rhône watershed (~5500 km2). Simultaneous observations of hyperconcentrated sediment-laden floods or debris flows in small sub-catchments (as small as 4 km2), suspended sediment concentration at the Rhône river mouth, and velocity profiles in the Rhône canyon demonstrate how localized storm events trigger turbidity currents in the canyon. Evidence that these turbidity currents can continue into the deep hypolimnion of Lake Geneva is provided. Preliminary estimations of the frequency of turbidity currents relative to their type of triggering and their contribution to the total sediment load discharged into Lake Geneva are discussed.

How to cite: Mettra, F., Blanckaert, K., Lemmin, U., and Barry, D. A.: Sediment transfer in the Rhône River Basin, Switzerland: the role of localized severe Alpine storm events on triggering turbidity currents in Lake Geneva, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7423, https://doi.org/10.5194/egusphere-egu21-7423, 2021.

Violaine Piton, Frédéric Soulignac, Ulrich Lemmin, Graf Benjamin, Htet Kyi Wynn, and Andrew Barry

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.

Marcel van der Perk

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.

John Robotham, Gareth Old, Ponnambalam Rameshwaran, David Sear, David Gasca-Tucker, Helena Soteriou, James Bishop, Ann Berkeley, David McKnight, and Joanne Old

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.