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HS2.3.7

EDI
Plastic in freshwater environments

Plastic pollution in freshwater systems is a widely recognized global problem with potential environmental risks to water and sediment quality. Furthermore, freshwater plastic pollution is also considered the dominant source of plastic input to the oceans. Despite this, research on plastic pollution has only recently expanded from the marine environment to freshwater systems. Therefore data and knowledge from field studies are still limited in regard to freshwater environments. Sources, quantities, distribution across environmental matrices and ecosystem compartments, and transport mechanisms remain mostly unknown at catchment scale. These knowledge gaps must be addressed to understand the dispersal and eventual fate of plastics in the environment, enabling a better assessment of potential risks as well as development of effective mitigation measures.
In this session, we explore the current state of knowledge and activities on macro-, micro- and nanoplastics in freshwater systems, including aspects such as:
• Plastics in rivers, lakes, urban water systems, floodplains, estuaries, freshwater biota;
• Monitoring and analysis techniques;
• Source to sink investigations, considering quantities and distribution across environmental matrices (water and sediment) and compartments (water surface layer, water column, ice, riverbed, and riverbanks);
• Transport processes of plastics at catchment and local scale;
• The role of river regulation structures, e.g. dams, navigation, flood control, etc., in plastic retention and transport
• Effects of hydrological extremes, e.g. accumulation of plastics during droughts, and short-term export during floods in the catchment;
• Degradation and fragmentation processes, e.g. from macro- to micro- and nanoplastics;
• Modelling approaches for local and/or global river output estimations;
• Legislative/regulatory efforts, such as monitoring programs and measures against plastic pollution in freshwater systems.

Convener: Marcel Liedermann | Co-conveners: Kryss Waldschläger, Daniel González-Fernández, Tim van EmmerikECSECS, Freija Mendrik
Presentations
| Tue, 24 May, 10:20–11:50 (CEST), 13:20–18:30 (CEST)
 
Room 3.29/30

Tue, 24 May, 10:20–11:50

Chairpersons: Marcel Liedermann, Kryss Waldschläger, Daniel González-Fernández

10:20–10:23
TB 1 - Plastics in freshwater environments & Modelling approaches

10:23–10:30
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EGU22-12841
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Highlight
Daniel González-Fernández et al.

Rivers act as pathways transporting anthropogenic waste from inland sources to the sea, including large quantities of plastic. Estuaries are rich and diverse environments where the interaction between fluvial processes and the tidal regime results in complex dynamics that affects residence time and net transport plastics in the water column. The use of plankton nets (small mesh sizes, e.g. < 500 µm) to collect microplastic samples allows characterizing plastic particles of different sizes. At the same time, given the variability in plastic particles abundance, the limitation in number of samples and/or volume filtered per sample, may cause a large bias in such characterization. Generally, particle abundance decreases toward larger particle sizes, and therefore the collection of representative samples for a certain plastic size range depends on sampling effort. Here, we analyze abundance and weight of micro- (< 5mm) and mesoplastics (5-25 mm) collected in estuarine waters at the River Guadalquivir through bi-monthly monitoring over one year. Our results demonstrate that establishing ratios between micro- and meso-plastics concentrations can lead to large uncertainties when a limited number of samples is used in the analysis, causing strong bias in the extrapolation of mass budgets for mesoplastics. Collecting representative samples for mesoplastics implies a change in the current monitoring methods to specifically target such particle size range.

How to cite: González-Fernández, D., Manzano-Medina, S., González-Duarte, M. M., and Cózar, A.: Monitoring mesoplastic concentrations in estuarine waters: A case study in the River Guadalquivir (Southern Spain), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12841, https://doi.org/10.5194/egusphere-egu22-12841, 2022.

10:30–10:37
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EGU22-12272
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ECS
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Highlight
Stephanie Andrews et al.

A ubiquitous contaminant across the globe, microplastic contamination is a growing issue of which the effects and consequences in the environment are relatively unknown. Freshwater systems, specifically rivers, are important in the translocation of microplastics from terrestrial sources to the marine environment. This makes it vital to understand the abundance and distribution of plastics within them and any potential effects on freshwater organisms. The River Thames is the second largest river in the UK and has multiple anthropogenic stressors and pathways of potential microplastic contamination along its trajectory. This study aims to determine the distribution and abundance of microplastics in the waters and benthic organisms that inhabit the River Thames. It will explore how location and proximity to sites of potential contamination, and feeding type influence the ingestion of microplastics in organisms. Water samples were collected from the river in May 2019 along with benthic dwelling organisms from 3 sites of suspected microplastic contamination. Initial findings reveal a high abundance of microplastics in water samples from the River Thames (average 3.55 mp/m3) and abundance increases along the trajectory of the river (1.05 mp/m3 at the highest sampling site increasing to 5.72 mp/m3 at the lowest sampling site). In all sites sampled, fragments and fibres were the most dominant particle shapes. Filter feeders ingested the highest abundance of microplastic fibres whilst grazers had the highest abundance of ingested fragments. The abundance of particles ingested by invertebrates differed across study sites showing varying levels of contamination. The presence of microplastics in a range of benthic taxa aligned with differences in dominant particle shapes in species with distinct feeding modes indicates widespread contamination with potential ecological impacts of microplastics in freshwater species of the River Thames.

How to cite: Andrews, S., Lewis, C., and Galloway, T.: The distribution and abundance of microplastics in the waters and organisms of the River Thames, UK., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12272, https://doi.org/10.5194/egusphere-egu22-12272, 2022.

10:37–10:44
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EGU22-9320
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ECS
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Rose Pinto et al.

Rivers have been highlighted to play a key role in the transport of plastics into the ocean and especially, urban water systems act as a major source of plastic leakage into the marine environment.  However, observed data on plastic pollution in these urban water systems are scarce.  Our study focuses on the Odaw river basin which is the main drainage systems in Accra, Ghana, and is heavily polluted with macroplastics.  This is due to the high anthropogenic activities which have increased the indiscriminate dumping of waste into the water system.  These macroplastics in the water system accumulates over long periods, and a part of it is emitted into the ocean during high discharges.  Due to limited data on the quantification of macroplastics in the Odaw river, the seasonality and hotspot accumulation zones of these macroplastics in the river are unknown.  Such information is crucial for policymakers to prioritize future plastic debris monitoring and mitigation strategies.  We aimed to quantify the macroplastic emissions from the Odaw river into the ocean.  Using visual plastic counting from four bridges together with a hydrodynamic model, estimations for total yearly plastic fluxes through the Odaw river were made.  This model used rainfall data from 2016-2021 at the input nodes to simulate the discharges in the water system.  We estimated a total plastic flux from the Odaw river into the ocean between 2.6 x 101 and 1.7 x 103 tons per year.  Low plastic fluxes were observed at the bridges during dry periods, but a 10 fold increase in plastic fluxes was observed during and after a rainfall event.  Except for two sampling days, negative plastic fluxes were observed at the two bridges closest to the ocean due to the effect of tides.  These observations made the estimation of the total plastic emissions into the ocean challenging because of the bidirectional flow dynamics of the macroplastics at these locations.  The findings of this study provide baseline data for macroplastic transport through the Odaw river into the ocean.  Future research could focus on investigating the accumulation zones of macroplastics at the bridges closest to the river mouths due to the role of tidal dynamics on the river plastic transport and export into the ocean.

How to cite: Pinto, R., Barendse, T., van Emmerik, T., Annor, F., Duah, K., Udo, J., Lugt, D., and Uijlenhoet, R.:  Macroplastic emissions from the Odaw river, Ghana, into the ocean., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9320, https://doi.org/10.5194/egusphere-egu22-9320, 2022.

10:44–10:51
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EGU22-3669
Simone Lechthaler et al.

Microplastics are detected in most environmental compartments and hence receive a great deal of attention, especially in aquatic environments where rivers act as pathways for microplastics. Currently, a particularly high input of microplastics through Asian rivers is assumed predominantly by modelling data, while field measurements are scanty.

Three rivers in South India were considered for this purpose to focus on their microplastic loads. The emphasis was on the comparison of microplastic concentrations in urban and rural rivers to identify if the anthropogenic influence control the loads. While two rivers in the megacity Chennai (Tamil Nadu) were found to have an average microplastic concentration of 0.4 microplastic particles/L, a rural river near Munnar (Kerala) had an average concentration of 0.2 microplastic particles/L. The results show higher loads in the urban area with a high anthropogenic influence by wastewater discharges and waste disposal through high number of residents dumping directly by the river. Fibres were the predominant shape (64.13%), black was the predominant particle colour (44.80%) and polyethylene and polyprolyene were the predominant polymers (each 46.67%) detected within the identified particles of all samples.

Rough estimates of annual microplastic discharge from the Adyar River (Chennai) into the Bay of Bengal are found to be as high as 11.6 trillion microplastic particles. This study, which is one of the first baseline studies for microplastic loads in South Indian streams, should be complemented with further environmental sampling during pre-monsoon, monsoon and post-monsoon seasons to get more detailed information on the storage and transportation of fluvial microplastics and to understand the seasonal effect on the river flow characteristics as well as the fate of microplastics.

How to cite: Lechthaler, S., Waldschläger, K., Sandhani, C. G., Sannasi Annamalaisamy, S., Vallam, S., Schwarzbauer, J., and Schüttrumpf, H.: Microplastics in Indian freshwater systems – is an anthropogenic influence measurable?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3669, https://doi.org/10.5194/egusphere-egu22-3669, 2022.

10:51–10:58
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EGU22-251
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ECS
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Ajay Kumar et al.

The occurrence, distribution, characterization and quantification of microplastics (MPs) and phthalic acid esters (PAEs) from the freshwater aquatic environment are not thoroughly explored in the Indian Himalayas despite concern over their adverse effects on human health and ecosystem. In this study, we have investigated the presence of MPs and PAEs in an aquatic system from Indian subcontinent. The MPs were detected in all water and sediment samples with abundances ranging from 02–64 particles/L and 15–632 particles/kg dw, respectively. The abundance of MPs, dominated by polyethylene and polystyrene, with the majority being fibres and fragments indicated that they were derived from plastic paints, boats or synthetic products. The concentrations of PAEs in the surface sediment samples varied from 06-357 ng/g dw. The most abundant PAEs in the sediments were dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP), since they were present in all the samples collected from the lake basin. The relatively higher abundances of MPs and higher concentrations of PAEs were generally found in the vicinity of areas impacted by anthropogenic activities. A clear correlation between the abundance of microplastics and PAEs concentration was observed suggesting that they are closely attributed to a single source. This study also provides an alternative approach to utilize the chemical additives in plastics as markers to trace the presence and distribution of MPs in the aquatic environment.

How to cite: Kumar, A., Behera, D., Bhattacharya, S., Mishra, P. K., Yadav, A., and Ambili, A.: Distribution and characteristics of microplastics and phthalate esters from a freshwater lake system in Lesser Himalayas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-251, https://doi.org/10.5194/egusphere-egu22-251, 2022.

10:58–11:05
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EGU22-205
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ECS
Milica Velimirovic et al.

The presence of small plastic fragments in open ocean water was first noticed in the 1970’s. Throughout the last decade, the scientific interest has been renewed and has pointed out that rivers may act as sinks for land-based plastic pollution and a potential major source of marine plastic debris, thus presenting an environmental threat. As a long-term consequence, plastic fragmentation will lead to pollution release that can impose a negative impact on river, as well as marine ecosystems, especially once they enter the food webs. As a result, this is a topic of increasing concern, but research on this issue is still in its early stages with fundamental gaps in the understanding of the sources, transformation pathways, fragmentation processes, fate of the land-based plastic pollution and estimates of the riverine plastic flux in general.

In order to identify the most polluting rivers and to prioritize mitigation efforts, accurate estimates of global riverine plastic emissions are required. The present work is aimed to give an overview of the morphology, size and composition of plastic debris found in the Sea Scheldt estuary (Belgium). For that purpose, in 2018, 3 sampling campaigns were performed by using an anchor netting technique with the mesh size of the nets progressively becoming smaller, reaching 5 mm at the tip of the nets. The samples originating from the Scheldt were separated into two categories based on their appearance (morphology) and size. The morphology consisted of 5 classes: fragments, foam, foil, filaments and pellets, whilst the size was divided into 6 categories: 0-2.5 cm (where 0 represents smallest size of the mesh being 5 mm); 2.5-5 cm; 5-10 cm; 10-20 cm; 20-30 cm; and larger than 30 cm. As a result, a grand total of 12,801 plastic items were collected. On average 1.6x10-3 items per m3 were found as suspended fraction of plastic debris in the Scheldt river. Foils were the most abundant with more than 88% of the samples being characterized as such, followed by fragments for 11% of the samples and filaments constituting less than 1% of the plastic debris. By using FTIR, polypropylene and polyethylene were identified as the most common polymers found with an abundance of more than 70%. This can be expected, as polypropylene and polyethylene make up for more than 50% of the plastic production in general. Finally, analysis of plastic debris by using μ-XRF spectrometry presents a good method for the identification of the mineral elements present. Ca, P, S and Si are the most abundant elements in the plastic debris, followed by Al, Fe and Ti.

M.V. is a senior postdoctoral fellow of the Research Foundation – Flanders (FWO 12ZD120N).

How to cite: Velimirovic, M., Teunkens, B., Ghorbanfekr, H., Buelens, B., Van Damme, S., Tirez, K., and Vanhaecke, F.: Macroplastics monitoring in the Sea Scheldt estuary , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-205, https://doi.org/10.5194/egusphere-egu22-205, 2022.

11:05–11:10
Discussion

11:10–11:17
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EGU22-1566
Tadanobu Nakayama and Masahiro Osako

Contamination of plastic materials in our environment has received more attention from the public, scientists, and policy makers during the last few decades. Though some of the models have succeeded to simulate the transport and fate of plastic debris in freshwater systems, a complete model is under development to elucidate the whole picture of plastic dynamics in the basin scale. One of the authors has so far developed a process-based eco-hydrology model, NICE (National Integrated Catchment-based Eco-hydrology) (Nakayama and Watanabe, 2004) and NICE-BGC (BioGeochemical Cycle) (Nakayama, 2017), and applied them to various basins from local/regional to continental/global scales. NICE-BGC can simulate iteratively nonlinear interactions between hydrologic, geomorphic, and ecological processes (water, heat, sediment, nutrient, and carbon cycles, etc.) (Nakayama, 2020). In this study, the authors extended NICE-BGC to couple with plastic debris model for freshwater systems, and applied it to all the first-class river basins in entire Japan (109 river basins). The new model included the advection, dispersion, diffusion, settling, dissolution and deterioration due to light and temperature, but assumed no interaction with suspended matter (heteroaggregation), resuspension, biofouling, and effect of wind, etc. The authors also assumed plastics as pure and totally inert polymers and spherical particles with constant size and density for model simplification. NICE-BGC simulated how mismanaged plastic waste (MPW) of about 36,000 ton/yr (Meijer et al., 2021) and point sources such as tyres, personal care products (PCPs), dust, and laundry in the entire country are transported from land to river, and finally to the ocean. The model showed the total flux of macro- and micro-plastics varies dependent on the removal efficiency of micro-plastic in wastewater treatment plants and the density of plastic. It was clear that only limited plastics discharged to land flows out into the ocean intensively during rainfall seasons, similar to plastic loading estimates in the previous study (Nihei et al., 2020). These results help to quantify the impacts of plastic waste on terrestrial and aquatic ecosystems, and find solutions and measures to reduce plastic input to the ocean.

How to cite: Nakayama, T. and Osako, M.: Evaluation of fate and transport of macro- and micro-plastics in terrestrial-aquatic continuum of entire Japan by developing a spatio-temporally explicit eco-hydrology model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1566, https://doi.org/10.5194/egusphere-egu22-1566, 2022.

11:17–11:24
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EGU22-76
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ECS
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David Mennekes and Bernd Nowack

Starting from plastic pollution in oceans as a widely recognized environmental problem, the research focus has also shifted towards rivers which were found to be a major inflow of plastics into the oceans. However, the source of plastic pollution itself is mostly upstream and for instance related to waste water treatment plants, littering of on-the-go consumer packages or agricultural films. For Switzerland a recent study modeled the release of the seven most used plastic polymers (LDPE, HDPE, PP, PS, EPS, PVC, PET) as micro- und macroplastic to the environment. Release maps of plastic emissions were obtained at high spatial resolution of 100 m by 100 m for soil grid cells and for each single river section in Switzerland. The aim of the current work was to couple this release model with its high spatial resolution to a model for the transport, accumulation and removal of the plastic polymers.

The model for the Swiss river and lake network allows to follow plastic pollution through every stream in Switzerland from the sources towards the outflows to the neighboring countries of Switzerland. We differentiate between the different plastic polymers and micro- and macroplastic. Furthermore, we consider physical properties (e. g. density, size) to establish parameters for accumulation and removal or cleaning rates of plastics in each river section and lakes based on parameters such as slope, urbanization or volume. In detail, we model the movement of plastic mass along the rivers based on average flow velocities while in lakes we consider sedimentation rates (accumulation) based on literature data. Input for the model is the yearly release of the seven polymers into about 2000 river sections. The transport model considers a network of over 600,000 river segments and 210 lakes. Our model provide contamination data on the scale of each river section which compared with so far available catchment scale model will provide an even closer look at rivers and local sources and sinks of plastics. However, many parameters regarding micro- or macroplastic transport in natural rivers at a large scale are still unknown or hydrological parameters on a country scale are not available. Therefore, a compromise between data availability and implementation of physical processes in the model had to be found. First results show the strength of our model to trace plastic particles regardless the size or polymer type. We are able to detect lakes as major sinks which substantially reduce plastic transport in rivers.

Our work can help to better understand the sources of the global plastic pollution but rises the need for experimental data on plastic transport in the environment. The large-scale understanding of plastic transport processes will provide policy makers with options were to tackle the spread of plastic pollution in the most efficient way.

How to cite: Mennekes, D. and Nowack, B.: Modeling polymer-specific exposure to micro- and macroplastics in freshwaters at high spatial resolution at the country-scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-76, https://doi.org/10.5194/egusphere-egu22-76, 2022.

11:24–11:31
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EGU22-3775
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ECS
Eshel Peleg et al.

Microplastic (MP) delivery from the terrestrial to aquatic environments is a global concern to many ecosystems and potentially also to humans. Currently, a limited number of models can accurately predict how MPs move through streams and rivers toward the oceans. The limited predictive power of classical colloid filtration theory and the lack of models that take into account the interactive effect between streambed characteristics, flow conditions and particle characteristics limit our ability to model the deposition of MP in streambeds. This study combines improved mechanistic prediction of colloid attachment with a model that predicts flow and transport of particles in a moving streambed to quantify MP deposition in streams. A set of numerical simulations were conducted using sand with D50 of 0.3 mm and hydraulic conductivity of 0.12 cm/s. Such sand is predicted to form ripples with a length of approximately 17 cm and a height of 1.9 cm. Coefficient of attachment (Katt) was predicted for simulated MP particles of four different densities (900, 1050, 1140, and 1350 (Kg/m3), which are typical densities of Polypropylene [PP], Polystyrene [PS], Polyamide [PA], Polyethylene terephthalate [PET], respectively. In addition, model scenarios included three colloidal sizes (0.5, 1, 10 μm) and various overlying stream velocities of 0.1-0.5 m/sec. Such stream velocities were predicted to yield bed celerities between 0-130 cm/hr. Hyporheic exchange flux between the stream and the bed increased non-linearly with celerity and was found to be ten times greater for the fast celerity (130 cm/hr at stream velocity of 0.5 m/sec) as compared to slow-moving bedform with the same geometry (10 cm/hr at stream velocity of 0.2 m/sec). Difference hyporheic exchange fluxes are also expected to influence the rate of MP delivery to the bed and their deposition. Initial simulations show that increased bedform celerity and Katt lead to a shallower depth of MP deposition and a more compact distribution in the bed. Increased celerity reduces deposition depth by flattening hyporheic exchange flow paths. Therefore, despite an increased flux of MP into the bed under high stream water velocity, deposition occurs at shallower depths, and the chance for resuspension due to erosion of the bed sediment increases. Quantifying the deposition rates and residence time in the bed is essential for understanding the transfer of MP through streams and rivers toward the oceans, developing sampling strategies, and finding long-term solutions for reducing their concentrations and the associated risks.

How to cite: Peleg, E., Johnson, W. P., Teitelbaum, Y., and Arnon, S.: Modeling microplastic deposition in sandy streams with moving bedforms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3775, https://doi.org/10.5194/egusphere-egu22-3775, 2022.

11:31–11:38
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EGU22-4402
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Highlight
Alena Bartosova et al.

Plastic pollution is one of the major global water quality issues. Yet the lack of consistent data and standardized monitoring leads to a wide range of estimates of plastic load that is being delivered to marine environment. At the same time, continental and global dynamic hydrological models have emerged as tools for e.g. flood forecasting, large-scale climate impact analyses, and estimation of time-dynamic water fluxes into sea basins. One such tool is a dynamic process-based rainfall-runoff and water quality model Hydrological Predictions for Environment (HYPE) and its global application, World-Wide HYPE (WWH, Arheimer et al., 2020). We present the first results simulating riverine plastic pollution in South Africa using a WWH submodel.

WWH was amended to include the population living within different sanitation conditions. Sanitation service type and safely managed fraction were estimated for each catchment by combining country and regional sanitation data (WHO, 2017) with human development index data (5 arc-min resolution; Kummu et al., 2020) and high-resolution (1km grid) settlement type and population (Pesaresi et al., 2019) datasets. This information was then linked to plastic waste generation, both in terms of mismanaged waste production and microplastics associated with municipal point sources.

Data on plastic flows and concentrations in various South African freshwater bodies were collected from published literature. Traditional model calibration techniques may not be appropriate in this case due to insufficient number of data points, large variability in plastic characteristics and sampling techniques, as well as large uncertainty and a lack of current knowledge of transport and transformation processes in water bodies. Thus, an ensemble of the models was developed by varying model parameters that affect generation, transformation, and transport of plastic from the various sanitation categories and in rivers. Collected data together with other global estimates were then used to evaluate the ensemble with a weight of evidence approach, highlighting sources and processes of major significance and focusing the ensemble towards a realistic set. This set will be used to further develop modeling routines at a large scale and provide guidance in developing the full global model.

References:

Arheimer, B., Pimentel, R., Isberg, K., Crochemore, L., Andersson, J. C. M., Hasan, A., and Pineda, L., 2020. Global catchment modelling using World-Wide HYPE (WWH), open data and stepwise parameter estimation, Hydrol. Earth Syst. Sci. 24, 535–559, https://doi.org/10.5194/hess-24-535-2020

Kummu, Matti; Taka, Maija; Guillaume, Joseph H. A. (2020), Data from: Gridded global datasets for Gross Domestic Product and Human Development Index over 1990-2015, Dryad, Dataset, https://doi.org/10.5061/dryad.dk1j0

Pesaresi, Martino; Florczyk, Aneta; Schiavina, Marcello; Melchiorri, Michele; Maffenini, Luca (2019): GHS-SMOD R2019A - GHS settlement layers, updated and refined REGIO model 2014 in application to GHS-BUILT R2018A and GHS-POP R2019A, multitemporal (1975-1990-2000-2015). European Commission, Joint Research Centre (JRC) [Dataset] doi: 10.2905/42E8BE89-54FF-464E-BE7B-BF9E64DA5218 PID: http://data.europa.eu/89h/42e8be89-54ff-464e-be7b-bf9e64da5218

World Health Organization. "Progress on drinking water, sanitation and hygiene: 2017 update and SDG baselines." (2017).

How to cite: Bartosova, A., Brendel, C., and Arheimer, B.: Ensemble modeling of plastic flows in South Africa’s rivers with a large-scale hydrological model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4402, https://doi.org/10.5194/egusphere-egu22-4402, 2022.

11:38–11:45
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EGU22-9806
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ECS
Pouyan Ahmadi et al.

Mismanaged waste leads to inputs of microplastics into the environment and the aquatic system affecting rivers and lakes. The physical properties of microplastic (MP) particles affect their terminal settling velocity (TSV) in the water column and in turn their distribution patterns in aquatic systems. To evaluate the settling behavior and the TSV of MP particles we simulated the settling of a large range of MP particles with regular and irregular shapes in the water column using a computational fluid dynamics (CFD) model. To validate the results returned by our model, we compared CFD findings to the corresponding results obtained by semi-empirical relationships as well as the results from experiments for 120 irregularly shaped MP particles with sizes and densities ranging from 500 to 2000 µm and 1.03 to 1.38 grcm-3, respectively. The CFD results are in good agreement with the results from the laboratory and semi-empirical relationships with a 0.05 difference in the slopes of their linear regressions. In a next step, we defined scenarios to systematically investigate the influence of different particle characteristics such as roundness, density, and volume as well as water temperature on the TSV of regular and irregular MP particles. Our simulations revealed a dominant effect of particle density on the TSV compared to the effects of the other parameters. For example, doubling particle densities increased the TSVs of the MP particles up to 500%, while, doubling their volumes only led to a maximum increase in their TSV of 200%. Increasing the roundness of the MP particles, letting them evolve towards a perfect sphere, increased their TSVs by up to 15%, while seasonal changes in lake water temperatures typical for lakes in temperate climate regions, caused changes in TSVs by up to 32%.

How to cite: Ahmadi, P., Elagami, H., Dichgans, F., Gilfedder, B., and Fleckenstein, J. H.: Evaluation of the Effects of Particle Characteristics on the Terminal Settling Velocities of Microplastics in Stagnant Waters using CFD, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9806, https://doi.org/10.5194/egusphere-egu22-9806, 2022.

11:45–11:50
Discussion

Tue, 24 May, 13:20–14:50

Chairpersons: Kryss Waldschläger, Tim van Emmerik, Marcel Liedermann

13:20–13:25
TB 2 - Monitoring and analysis techniques & Effects of hydrological extremes

13:25–13:32
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EGU22-1044
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ECS
Batdulam Battulga et al.

Plastic debris has been recognized as one of the carriers of hazardous substances in the aquatic ecosystem due to its ubiquitous distribution and potential interaction with pollutants through developed biofilms. Although an increasing number of studies have highlighted that diverse microbial species including biofilm-forming microorganisms are colonized on the plastic surfaces in aquatic environments, biofilm-mediated interactions between plastics and pollutants especially radionuclides remain unclear. In this study, we aimed to extract biofilms from the environmental plastics using a newly developed extraction method and to determine the concentration of radiocesium (137Cs) and stable isotope ratios (δ13C and δ15N) in the extracted biofilm samples. Visible plastics were collected from the mouths of coastal rivers in Ibaraki prefecture, Japan. Although the plastic concentration along the river mouth was not evaluated in this study, various abundances (96 – 1868 pieces), sizes (1 – 50 mm), colors, and morphotypes of plastics were applied to the extraction procedures. After plastic and biofilm separation with ultrasonication, biofilm samples were collected by the two ways: freeze-drying (15.5 – 44.4 mg); and freeze-drying after syringe treatment (14.5 – 65.4 mg). The XRD diffractograms of biofilm samples confirmed that biofilms obtained by freeze-drying only were still heterogeneous and the agglomerations of organic substances, mineral particles, and small microplastics (MPs, <1 mm). The results also demonstrated that biofilm extraction was achieved by syringe treatment separating the mineral and small MP particles, resulting in homogenous biofilms from the surface of plastics. Preliminarily results of 137Cs activity concentrations in heterogenous (ranging from 0.22 to 0.54 Bq g−1) and homogenous (0.82 ± 0.04 Bq g−1) biofilm samples revealed that plastics serve as a carrier for 137Cs in the coastal river environment mediated by developed biofilms. As a result of the presence of petroleum-derived small MPs, heterogeneous biofilm samples showed a relatively lower δ13C value (−26.03 ± 0.34‰; mean ± SE) compared with homogenous biofilm samples. A similar trend was observed in the δ15N values. Our results suggest that developed biofilms on the plastics might have specific signatures of δ13C and δ15N depending on the source and pathway of the organic matter. The study contributes to the knowledge of the developed biofilms on environmental plastics and their potential interactions with 137Cs in the coastal aquatic environment.

Keywords: environmental plastics, biofilm, coastal river, radiocesium, stable carbon and nitrogen isotopes

How to cite: Battulga, B., Atarashi-Andoh, M., and Koarashi, J.: A new approach to extracting biofilm from environmental plastics using ultrasound-assisted syringe treatment for isotopic analyses , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1044, https://doi.org/10.5194/egusphere-egu22-1044, 2022.

13:32–13:39
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EGU22-7423
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ECS
Tianlong Jia et al.

Plastic pollution in rivers is a serious environmental concern. To improve the monitoring of floating macro-plastic litter in water, researchers increasingly resort to automatic detection tools based on Artificial Intelligence (AI) for Computer Vision (CV). The most advanced applications feature Deep Learning (DL) methods based on Convolutional Neural Networks (CNN) achieving state-of-the-art performances in standard CV datasets (e.g., ImageNet).

Despite promising initial results, only few studies validated the generalization ability of DL models across different locations, environmental conditions, and instrumental setups. Poor generalization results in the need for a new model for each different setting. This increases the data requirements and limits the applicability. These aspects are essential for practical implementations such as the development of a structural monitoring strategy backed by a reliable AI model.

In this work, we discuss how to develop a robust DL methodology by harnessing recent advancements in AI, such as data-centric AI and semi-supervised learning. We also show the effects of implementing these techniques on the generalization performances of a DL model by employing two different datasets of floating macro-plastic in rivers. The first is a new dataset recorded in a semi-controlled environment featuring a small drainage canal in the Netherlands; the second is a dataset available from the literature, with images from different waterways in Jakarta, Indonesia. The significant diversity among the two datasets grants a sound evaluation of model generalization performances and on the suitability of the proposed methodology for achieving increased robustness.

How to cite: Jia, T., de Vries, R., Kapelan, Z., and Taormina, R.: A robust deep learning methodology to detect floating macro-plastic litter in rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7423, https://doi.org/10.5194/egusphere-egu22-7423, 2022.

13:39–13:46
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EGU22-1889
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ECS
Collin J. Weber et al.
13:46–13:53
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EGU22-8796
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ECS
Jan-Pascal Boos et al.

Rivers and streams are a primary transport vector for microplastics (MPs), connecting terrestrial sources to marine environments. While previous studies indicated that pore-scale MPs can accumulate in streambed sediments, the specific MPs transport and retention mechanisms in fluvial systems remain poorly understood. We present a novel method for a quantitative analysis of the spatiotemporal transport and retention of pore-scale MPs in an experimental flume. A continuous mass balance for MPs in surface water was achieved using two online fluorometers, while a laser-induced Fluorescence-Imaging-System was developed to track and quantify the spatial migration of MPs through the streambed sediments. The detection limit was <1 μg/L for 1 μm polystyrene microbeads with the fluorometers and 3 μg/L for the Fluorescence-Imaging-System. The system was able to quantitatively track the advective transfer of MPs into the streambed sediments: a process that has yet not been observed experimentally. Results showed that MPs infiltrated into the streambed sediments up to a depth twice the bedform amplitude. This work provides a novel experimental method to quantitatively monitor MP transport through porous media and advective exchange of MP across the streambed interface.

How to cite: Boos, J.-P., Gilfedder, B., and Frei, S.: Using fluorometric techniques to quantify microplastic transport in an experimental flume, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8796, https://doi.org/10.5194/egusphere-egu22-8796, 2022.

13:53–14:00
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EGU22-9060
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ECS
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Finn Begemann et al.

Macrolitter in aquatic environments is an emerging environmental risk, as it negatively impacts ecosystems, endangers aquatic species, and causes economic damage. One of the major reservoirs of macrolitter in aquatic environments are riverbanks. To effectively clean riverbanks and prevent future litter from accumulating in these reservoirs, robust monitoring techniques are needed that allow for quick, but reliable, assessments of the type, size and mass of macrolitter in these reservoirs. Here, we present a unique dataset of more than 16,000 anthropogenic litter items in the Dutch Rhine, Meuse and IJssel rivers. With this dataset, we facilitate making considered decisions for developing future monitoring strategies. Items were collected on 8 different riverbanks once per month for one year. Items were collected at upstream and downstream locations along the Dutch part of the rivers, and were categorized (river-OSPAR), weighed and measured. The dataset shows that the majority of the found items is plastic, especially fragments of foam, soft plastics (foils), and hard plastics. The composition of litter type varies more in space than in time, indicating that the spatial resolution of a future monitoring campaign outweighs the importance of the temporal resolution. We performed a Monte Carlo analysis to determine sample size requirements to calculate a representative number of average item mass. Up until 8,900 items are needed for an accurate representation of average items mass, depending on item category uniformity. Finally, a method is proposed to determine on which item size should be focused. The presented dataset can be used in future research, modelling practices and development of management strategies. 

How to cite: Begemann, F., de Lange, S., Mellink, Y., Vriend, P., Tasseron, P., and van Emmerik, T.: 16,000 riverbank litter items – A data driven approach to optimizing riverine plastic monitoring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9060, https://doi.org/10.5194/egusphere-egu22-9060, 2022.

14:00–14:07
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EGU22-9938
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ECS
Katrina Kremer et al.

Plastics are omnipresent in our daily lives, and this has a profound yet poorly understood impact on our health and environment. Since the 1950s, plastics consumption has strongly increased across the globe. Large amounts of this plastic is not recycled and is disposed into the environment. Through fluvial systems, plastics are transported and are deposited in reservoirs such as lakes and oceans where the plastics accumulate in the sedimentary systems. Thus, sediments which contain these plastic fragments can be used to assess their fate pathways, mass loads and accumulation rates in different environmental systems. This study aims to assess the plastics contamination in lake sediments, particularly for the microplastic size fraction (< 1mm) within an artificially ventilated lake, Lake Hallwil, Switzerland. We aim to understand plastics temporal deposition and understand accumulation areas. For this purpose, we retrieved short gravity sediment cores to study the temporal deposition history of plastics.  In addition, surface sediment samples have been taken from different locations within the lake basin for the geographical distribution of plastics. In order to quantify microplastics in sediments, the particles must be extracted from the lake sediments before further identification and characterization.

In this contribution, we present (1) the workflow to separate microplastic particles from the sediments and (2) the first data for the temporal evolution and the geographical distribution of the microplastic contamination recorded in lake sediments.

Using these first results, we plan to further expand the study to better understand the pathways of microplastics into lakes to assess specific release scenarios and mass concentrations of plastics from urban to natural areas surrounding Lake Hallwil, and compare these results to other lake systems.

How to cite: Kremer, K., Fabbri, S., Rast, D., and Zimmerli, M.: Microplastics contamination in an artificially ventilated Lake (Lake Hallwil, Switzerland), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9938, https://doi.org/10.5194/egusphere-egu22-9938, 2022.

14:07–14:14
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EGU22-11959
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ECS
Mattis Wolf et al.

Plastic waste finds its way to the ocean often through rivers: it is estimated that between 1.15 and 2.41 million tons of plastic waste enters the ocean every year from rivers. Out of the 1500+ rivers that are estimated for being responsible for 80% of the riverine plastic emissions, around 70 of these rivers are located in Vietnam which highlights the importance of further investigating the plastic waste situation in its rivers.

The aim for this study was to develop a method for machine learning based measuring several types of plastic litter (in particular floating, trapped and submerged) in riverine systems. By considering the combined information of various litter categories this methodology is able to draw a holistic picture of plastic transport in riverine systems.

Two different methodological components were set up: (i) an AI (artificial intelligence) based litter detection algorithm which analyses imagery gathered by bridge-installed action cameras for floating and trapped plastic waste items in terms of abundances and waste types and (ii) a net-based sampling method which measures floating as well as submerged plastics at the bridge locations. The applied AI-based litter detection algorithm was originally developed for plastics detection in an aquatic environment in Cambodia for drone imagery. Within this framework, this approach was further developed and applied to detect floating and trapped plastic litter in polluted rivers captured with action cameras in Vietnam. The complementing net-based sampling for submerged plastics was applied in parallel to calibrate the continuous camera-based sampling with direct measurements.

Within this study it was shown that the combination of the two presented approaches provides a suitable methodology for the measurement of plastic transport along a river. Calibration of the continuous camera-based method showed that about 50% of the litter was transported at the surface and was thus directly detectable by AI. The methodology is relevant to the remote sensing community focusing on plastics detection and to researchers addressing plastic waste. The continuous assessment of plastic quantities transported by rivers will be key for policy makers to identify main polluters and to understand the impacts of any taken measures to reduce plastics pollution. Increasing the understanding of plastic types through these measurements is key for policy makers to develop the right measures which can target the items responsible for the majority of plastics pollution in rivers, as typically only few items are responsible for the majority of plastics leakage. The achievements of this study aim to fill these knowledge gaps by enhancing the litter detection method. As a next step, this method could be scaled up to be tested for a longer time period and at additional sites. The results of such longer-term measurements of surface and submerged plastics may allow for extrapolation of floating plastics to total transported plastics.

How to cite: Wolf, M., Liedermann, M., El-Arini, A., Pessenlehner, S., Sattler, K., and Zielinski, O.: Method for AI-enhanced litter detection in aquatic environments using action cameras combined with net-based device for measuring submerged plastics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11959, https://doi.org/10.5194/egusphere-egu22-11959, 2022.

14:14–14:21
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EGU22-12172
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ECS
Paolo Tasseron et al.

Plastic pollution in aquatic ecosystems has increased dramatically in the last five decades, with strong impacts on human and aquatic life. Recent studies endorse the need for innovative approaches to monitor the presence, abundance, and types of plastic in these ecosystems. One such approach gaining rapid traction in the remote sensing community is the use of hyperspectral cameras to identify floating plastic litter. However, most experiments using this approach have been conducted in controlled laboratory environments, making findings exceptionally challenging to apply in natural environments. We present a method that links lab- and field-based identification of macroplastics using hyperspectral data (1150-1675 nm). Two experiments using riverbank-harvested macroplastics were set up in (1) a laboratory environment, and (2) at the Rhine River. The reflectance characteristics of the sample items were analysed to understand the influences of the two environmental settings. Eleven lab-based images (n = 786.264 pixels) and two field-based images (n = 40.289 pixels) were used for these analyses. Next, multiple classifier algorithms such as support vector machines (SVM), spectral angle mappers (SAM) and spectral information divergence (SID) techniques were applied, because of their robustness to varying light intensities and high accuracies in mapping spectral similarities. Our results showed that SAM classifiers are most robust in separating plastic debris from natural or human-made background elements, such as vegetation, quay walls, and sand. By applying lab-based spectral data for plastic detection in our field-based images, we were able to attain user accuracies up to 93.6% (n = 8.370 plastic pixels) using SAM. The same approach resulted in accuracies of 50.2% and 65.4% for SID and SIDSAM, respectively. The limitations of this study concern the low number of images used for training and classification, hardware issues related to the hyperspectral camera, and the unforeseen dynamic nature of environmental conditions outside a laboratory. Nevertheless, this study provides key fundamental insights in linking lab-based data to plastic detection in the field. In doing so, a contribution to the development of future spectral missions to monitor plastic pollution in aquatic ecosystems is made.

How to cite: Tasseron, P., Schreyers, L., Peller, J., Biermann, L., and van Emmerik, T.: Tackling the challenge between lab- and field-based detection of floating plastics using hyperspectral remote sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12172, https://doi.org/10.5194/egusphere-egu22-12172, 2022.

14:21–14:28
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EGU22-12712
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ECS
Anouk Boon and Frans Buschman

Plastic pollution has become a threat to both nature and humans. A substantial amount of plastic is transported in rivers towards the sea. Insight in the sources and transport in rivers, and how this is changing with conditions like discharge, is needed to plan effective mitigation strategies. Current measurement techniques mostly target floating items, recent studies however suggest that suspended plastics form a significant part of the total riverine plastic transport. Despite being successful, recently applied sampling techniques using several nets in the vertical are too invasive, expensive and labour intensive to apply on large spatial and temporal scale. A non-invasive and continuous measurement technique of suspended plastics, applicable on a large scale, is needed.

 

Sonar has shown potential for plastic detection. During measurements, a high-frequency acoustic signal is transmitted. This signal is scattered by water and suspended particles. Using an Acoustic Doppler Current Profiler (ADCP), the chosen sonar device, flow velocity can be obtained using the frequency shift of the signal. Aside from the frequency shift, also the strength of the returned acoustic signal can be measured. This backscatter strength depends on the size, form and material of the sampled object. It is nowadays used to estimate suspended sediment concentrations, but also relatively large objects like fish, organic matter and macro-plastics can be recognised by high backscatter intensity. As ADCPs have been broadly used for decades, current and historical data from a large network of measuring devices are available for analysis of plastic transport and its fluctuations. We propose steps for a method to quantify the macroplastic concentration from ADCP data.

 

During the study, a RDI StreamPro ADCP is horizontally mounted in a basin. Macroplastics differing in shape, size and polymer type are sampled 5 times within a period of 10 seconds, on three different distances (around 1, 3 and 5 meter) from the transducer. Almost all plastic items show a significantly higher backscatter intensity than the background signal, on all measurement distances. In contrast to net-based measurements, rotation is found to be an important aspect in the identification of items during ADCP measurements. To further develop the detection method, analysis of ADCP field data containing the usual background noise, combined with net measurements for validation, is needed. Expectation is that net measurements, used to make an estimate of the fraction organic material and plastic, are only needed periodically to make a good continuous estimate of macroplastic transport using ADCP data.

How to cite: Boon, A. and Buschman, F.: Revealing underwater plastics: Detection of suspended macroplastics using acoustic backscatter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12712, https://doi.org/10.5194/egusphere-egu22-12712, 2022.

14:28–14:35
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EGU22-12856
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ECS
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Highlight
Lauren Biermann et al.

Water hyacinths appear to play an important role in gathering and transporting macroplastic litter in riverine ecosystems. These fast-growing and free-floating invasive freshwater plants tend to form large patches at the water surface, which makes it possible to detect and map them in freely available imagery collected by the European Space Agency (ESA) satellites. In polluted rivers, hyacinth may thus serve as a viable proxy for macroplastics. However, at the ~10m spatial resolution offered by the Sentinel-1 and Sentinel-2 satellites, it’s not possible to discriminate smaller items of plastic caught up within large plant patches.

We present a case study from the Saigon River around Ho Chi Minh City, Vietnam. Here, we were able to successfully discriminate plastic debris within hyacinth patches using MAXAR Worldview-3 multispectral optical data (1.24m) and panchromatic imagery (0.31m). For the optical data, we selected the ACOLITE atmospheric correction and applied a novel detection index that leveraged the panchromatic band and the red band (band 5) to highlight differences between vegetation and debris. This approach allowed for the detection of riverine plastics within hyacinth patches floating downstream from Ho Chi Minh City towards the coast. Initial results from the Han River and coastal waters of Da Nang in Vietnam suggest that our plastic litter discrimination method is transferable to other aquatic environments. This research is preparatory for further remote sensing monitoring of 'plastic plants' in riverine ecosystems, and will be supporting clean-up operations being trialled in 2022.

How to cite: Biermann, L., Schreyers, L., van Emmerik, T., Bui, T.-K., Ling, Y., and Streett, D.: Finding Riverine Plastics in Floating Plant Patches using Worldview-3 Satellite Imagery, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12856, https://doi.org/10.5194/egusphere-egu22-12856, 2022.

14:35–14:42
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EGU22-3582
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ECS
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Highlight
Rahel Hauk et al.

The majority of mismanaged plastic waste does not reach the oceans, and rather accumulates in terrestrial and freshwater environments. Since 2017, riverbanks along the Dutch part of the river Meuse have been monitored by volunteers in spring and fall. At each monitored riverbank macroplastic and other litter items were collected along a 100 m section and classified in over 100 specific item categories. In July 2021, the Meuse was hit by a severe flood event with an estimated return period between 100 - > 1000 years, similar to other rivers in Germany, France, Belgium, and the Netherlands. Flood conditions can highly increase plastic (re)mobilization and transport within river systems, and plastic discharge into the oceans. However, the impact of a severe flood event on plastic litter accumulation on riverbanks, to the authors knowledge, was never measured before. Within three weeks after the flood event we counted and classified macroplastic and other litter items on 25 riverbanks along the Meuse, from the Dutch-Belgian border to the river mouth. The additional sampling allows us to, for the first time, assess the impact of such a flood event on plastic accumulation on riverbanks. In this presentation we compare plastic accumulation on riverbanks after this flood event to plastic accumulation during normal conditions. We compare the amounts and types of litter, and possible litter sources. This study aims to contribute to better understand mobilization, transport, and accumulation dynamics of plastics in river systems, and the role and impact of extreme events on plastic accumulation on riverbanks.

How to cite: Hauk, R., van Emmerik, T., Boonstra, M., de Winter, W., and van der Ploeg, M.: Plastic accumulation on riverbanks after the July 2021 Meuse flood, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3582, https://doi.org/10.5194/egusphere-egu22-3582, 2022.

14:42–14:50
Discussion

Tue, 24 May, 15:10–16:40

Chairpersons: Daniel González-Fernández, Kryss Waldschläger, Tim van Emmerik

15:10–15:13
TB 3 - Source to sink investigations & The role of river regulation structures in plastic retention and transport

15:13–15:20
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EGU22-327
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ECS
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Verena Levy Sturm et al.

Microplastic (MP) is ubiquitously found in aquatic environments and poses a risk to organisms and potentially also to human health. While MP in oceans was studied extensively in recent years there is still a lack of knowledge especially on how MP is being transported and deposited in streams. We conducted flume experiments to study how plastic properties and bedform movement influence the deposition dynamics of MP. We used a recirculating stainless-steel laboratory flume (650 cm x 20 cm), that was packed with homogeneous sand (D50=0.65 mm). We compared the deposition dynamics of MP under stationary bed and under fast moving bedforms. We used aged MP fibers made from PET, PP, PA at various lengths (25, 100, 200 μm). The deposition rates were quantified by adding MP into the water and tracking their concentration in the stream water over time. In addition, streambed samples were taken to quantify and analyze the locations and concentrations of MPs within the sediment. It was found that the physical properties of MP including size, density, and type had a relatively minor influence on their deposition rate because the mechanism was dominated by the movement of the bedform and not due to their transport within the porous medium. Only a slight difference in deposition rate was observed for the different types of MP. The MP particles that we used are too large to be efficiently transported into the porous media and the resulting patterns were deposition close to the water-sediment interface in stationary bed, and below the moving fraction of the bed for moving bedforms. These experimental results represent unique observations of the transport mechanisms of MP in streams with moving bedforms. They are important for the understanding of the transfer of MP from its source toward the oceans, for understanding the life cycle of plastics in the environment, to develop sampling strategies in streams, and to find long-term solutions for reducing their concentrations and the associated risks.

How to cite: Levy Sturm, V., Gobrecht, S., Bernstein, R., and Arnon, S.: The effects of stream water velocity, streambed celerity, and particle properties on microplastic deposition in streams, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-327, https://doi.org/10.5194/egusphere-egu22-327, 2022.

15:20–15:27
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EGU22-440
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ECS
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Highlight
Lisa Watkins and Jordan Yu

Intercepting mismanaged waste before it reaches the ocean is key to addressing global plastic pollution and its associated ecological effects. A successful strategy for disrupting the transport of macro debris is “trash traps”, cages and booms currently deployed in rivers worldwide to capture floating items. Existing traps are largely managed by NGOs and municipalities, many of whom collect comprehensive data on all captured trash. These community datasets provide a substantial, largely untapped opportunity to advance scientific understanding of riverine plastic pollution.

For this study, we partnered with Chattahoochee Riverkeeper, an NGO in Atlanta, U.S.A. that manages 11 trash traps across 6 rivers spanning a spectrum of urban to agricultural watersheds. After each rainstorm, NGO staff assess all captured debris according to U.S. Environmental Protection Agency Escaped Trash Assessment Protocol (ETAP), noting total volume and weight of the contents, as well as each item’s condition, material-type (e.g. glass, metal), and use (out of 41 item categories).

We analyzed data from each of their 281 trap collections occurring between 2019 and 2021, which captured 8904 items. We found that 80% of collected trash was plastic, with the most common item types being plastic bottles, Styrofoam and plastic bags. Their system of 11 trash traps intercepted 5.7 kg/day of trash from the Chattahoochee River watershed (median: 0.4 kg/day/trap). Though this amounts to 2 tonnes of trash in these tributaries annually, it’s the equivalent of each watershed resident contributing less than a water bottle each year (5.6 g/person/yr), supporting the need for centralized or system-scale pollution intervention strategies over distributed ones. To explore potential drivers of macroplastics, we utilize a general mixed effects model and find rainfall, watershed imperviousness, and local human engagement to be significant predictors of captured quantity. The model coefficients indicate, however, that these factors may be less important to macroplastics than they traditionally are for other river-transported pollutants. We suspect this is due to macroplastics being highly affected by harder-to-capture human activities.

In our presentation we explore these findings in the context of other macroplastic studies worldwide. Through this work, we hope to highlight how collaborative research principles can be used to leverage the local expertise and abundant, underutilized data of NGOs for the advancement of riverine plastic science, while also better engaging local communities around solutions.

How to cite: Watkins, L. and Yu, J.: Leveraging community data to characterize river macroplastic pollution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-440, https://doi.org/10.5194/egusphere-egu22-440, 2022.

15:27–15:34
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EGU22-1211
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ECS
Karolina Skalska et al.

Rivers form major conduits for land-derived plastic waste, with the annual emission of plastics to the world’s oceans currently being quantified at as much as 2.7 million metric tons. In particular, riverbed sediments have been found to retain high levels of microplastics (plastics <5 mm in size) and multiple studies reported microplastic concentrations in the sediments to exceed those in the water column by as much as 600,000 times. Emerging evidence suggests that high flows may remobilise some of the sedimentary microplastic pool, resulting in high microplastic loads entering the adjacent seas following flood events. However, the transport mechanisms that microplastics undergo in river settings remain poorly understood.

In this study, we investigated spatio-temporal variations in the microplastic contamination within river bed sediments in the R. Thames (UK) catchment. Sediment samples were taken on a seasonal basis over 3 years (2019-2021) from 12 sampling sites (classified as rural, urban and industrial) located on the main R. Thames and 8 of its tributaries. Microplastics were extracted from sediment using density flotation, then visually counted and investigated using a combination of ATR-FTIR and µATR-FTIR (Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy). Additional SEM analysis was carried out to describe the morphology (degradational patterns/occurrence of biofouling) of extracted microplastics.

Microplastics were present in most sediment samples (85%), with fragments being the dominant shape (92% across all seasons), followed by beads/pellets (5%) and fibres (3%). Microplastic levels varied on a seasonal basis (0 - 4,200 MP·kg-1 range), increasing in the summer months and decreasing in the winter by up to 89%. This suggests the occurrence of microplastic accumulation in the summer low-flow conditions followed by subsequent flushing of microplastics as a result of higher winter flows. Inter-site variations in microplastic levels were evident in the summer months, with concentrations increasing in the order of industrial>urban>rural. Microplastics were also more abundant at inner river banks and near point sources (e.g. effluent outlets). In contrast, such inter- and intra-site variations were less clear in the winter. Urban and rural samples were dominated by fragments (96% on average) irrespective of season, with most items made out of polyethylene (PE), but also containing thermoplastic elastomers found in road marking paints (e.g. ethylene vinyl acetate (EVA), polyamide (PA)). Although samples taken from industrial locations were also dominated by fragments (84%), they contained higher numbers of microbeads and industrial pellets (12%) composed of polymers widely used for industrial applications (e.g. poly(methyl methacrylate) (PMMA) used as Perspex glass, poly(diallyl phthalate) used in the processing of thermosetting plastics and resins, or poly(1,4-butylene terephthalate) (PBT) used for insulation purposes in the electrical industry).

Our study reveals a multitude of microplastic sources contributing to the pollution of the R. Thames catchment and confirms the existence of a strong seasonal pattern in microplastic deposition within riverbeds, suggesting a need to account for this process in the global models of microplastic export from land to sea.

How to cite: Skalska, K., Ockelford, A., Ebdon, J. E., Cundy, A. B., and Horton, A. A.: Spatio-temporal variations in microplastic presence and composition in the sediments of the R. Thames (UK) and its tributaries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1211, https://doi.org/10.5194/egusphere-egu22-1211, 2022.

15:34–15:41
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EGU22-1275
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ECS
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Highlight
Maciej Liro et al.

Amounts of macroplastic debris stored on different elements of mountain rivers are unknown, but such data are crucial to plan future mitigation activities in these fragile ecosystems. We determined the amounts of macroplastic stored on different surface types (geomorphic units and wood jams) in two reaches of the Dunajec River in the Polish Carpathians. A wide, multi-thread reach stored 36 times more macroplastic per 1 km of river length than the upstream-located narrow, channelized reach (1495.4 kg vs. 41.8 kg). In the multi-thread reach, 43.8% and 41.1% of macroplastic was stored on wooded islands and wood jams that covered, respectively, 16.7% and 1.5% of the area of active river zone. The median of macroplastic mass stored on wood jams equalled 113.2 g/m2 and was 180 times higher than on exposed river sediments, 129 times higher than in the areas overgrown with herbaceous vegetation and 19 times higher than on wooded islands. The results indicated that multi-thread reaches of mountain rivers supporting extensive wooded islands and numerous wood jams are hot-spots of macroplastic storage, whereas channelized reaches lacking these surface types act as transport reaches for macroplastic debris. Thus, multi-thread reaches of mountain rivers in populated areas can be used as target zones for river cleaning actions and downstream ends of channelized reaches as the location for installation of macroplastic trapping infrastructure.

How to cite: Liro, M., Mikuś, P., and Wyżga, B.: First insight into the spatial pattern of macroplastic storage in a mountain river, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1275, https://doi.org/10.5194/egusphere-egu22-1275, 2022.

15:41–15:48
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EGU22-1285
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ECS
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Highlight
Jen Drummond et al.

Wastewater treatment plants (WWTPs), are known sources of microplastics (1-1000 µm) to receiving streams. We analyzed surface water and streambed sediments at ~1km downstream of a WWTP in a rural stream near Birmingham, UK. To assess the temporal variation in microplastic transport and accumulation, we conducted a total of five sampling campaigns to sample both during high and low flow conditions. Point sampling was supported by semi-continuous measurements of flow and electrical conductivity to characterize the stream hydrologic conditions, especially in response to the WWTP effluent. We used the high frequency flow data as input to a mobile-immobile model for microplastic transport in streams that can account for the exchange between the surface water and streambed sediments, deposition and resuspension during baseflow and stormflow conditions. By combining the model with the less frequent microplastic measurements, we estimated inputs from the wastewater treatment plant and timescales of microplastic deposition and retention in the stream. Our findings advance the understanding of the interplay between microplastics depositing during low flows and resuspending during high flows, to improve predictions of microplastic fate and transport in river systems.

How to cite: Drummond, J., Schneidewind, U., Brekenfeld, N., Nel, H., Haverson, L., Kukkola, A., Sambrook-Smith, G., and Krause, S.: Microplastic accumulation in streambed sediment downstream of a wastewater treatment plant in response to dynamic flow conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1285, https://doi.org/10.5194/egusphere-egu22-1285, 2022.

15:48–15:55
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EGU22-1528
Stefan Krause et al.

Microplastic pollution has been found to be ubiquitous in freshwater ecosystems around the world, with global models predicting river network contributions to the oceans to present major and still increasing sources of marine plastic waste. While previous research has to a large degree focussed on identifying potential sources of plastic pollution to freshwater ecosystems (such as wastewater treatment plants, storm sewers, urban areas), and attributing these to observed microplastic pollution patterns in river corridors, little is known under what conditions potential pollution sources become activated and connected to surface waters, and how the fluvial transport of different micro- and nanoplastic size fractions determines spatial patterns of plastics along river networks, including long-term deposition, storage and potential resuspension.

This paper integrates field-based evidence of our global river microplastic survey and several comparative large river network studies (including the rivers Ganges, Boulder Creek, Rhone, and others) with river basin to global scale plastic fate and transport models to identify major drivers of hotspots and hot moments of riverine plastic pollution. Our results highlight under what conditions prior knowledge of the source distributions of plastic pollution carries significant predictive capacity for expected river corridor microplastic concentrations and when (and where) these patters can get transformed substantially by fluvial transport (and transformation) processes. Fusing this experimental evidence with our model predictions revealed significant differences in the downstream footprint, longevity and legacy of dominant sources and transport controls of plastics in the water column and in streambed sediments, driven by gravitational settling, hyporheic exchange flow and resuspension processes.  

How to cite: Krause, S., Nel, H., Schneidewind, U., Kukkola, A., Drummond, J., Kelleher, L., Lynch, I., Sambrook Smith, G., Runkel, R., Allen, D., Allen, S., Wazne, M., Dendievel, A.-M., Simon, L., Mermillod-Blondin, F., Haverson, L., Yonan, Y., Mourier, B., Piegay, H., and Gomez-Velez, J.: Source activation or fluvial transport – dynamic controls on spatial patterns and temporal dynamics of plastic pollution in river corridors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1528, https://doi.org/10.5194/egusphere-egu22-1528, 2022.

15:55–16:02
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EGU22-1804
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ECS
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Khoa Thi et al.

Recent studies suggest that more land-based plastics are accumulated and remobilized in riverine environments than exported to the ocean. Hydrodynamics and other factors like wind drag and navigation can drive plastics to riverbanks, where they can be retained in plants, on floodplains, or in stagnant water bodies. With this study, we provide additional observational evidence that a substantial share of floating plastics may not flow downstream. Every week from May to December 2021, we measured floating plastics at three bridges located in the Hong-Duong bifurcation of the Red River, Vietnam. These locations were chosen to monitor both the input plastics entering the bifurcation and the output plastics exiting the bifurcation in both branches. The upstream location is Nhat Tan, which is located on the Red River in northern Hanoi. The downstream location on the main stream is Long Bien, approximately 8 kilometers south of Nhat Tan on the Red River, while the third location is in Dong Tru, on the distributary Duong River, about 7 kilometers from Nhat Tan. We collected data on the plastic mass balance of various plastic categories in the bifurcation, including PET, PO-soft, PO-hard, multilayers, PS, and PS-E. The results indicated that the plastic mass balance does not close in general; there is more plastic upstream than in the two downstream locations combined. The dry season, from October to December, was more balanced, with a 4% difference. Meanwhile, between May and September, approximately 16% of floating plastics were discovered to be missing. Additionally, the majority of floating plastics remained in the main stream, with only 8% entering the distributary, and the division rate kept constant throughout the study period. However, the balance differed for specific categories. Five categories had missing downstream records compared to upstream, and PO-soft featured a more intricate balance mechanism with alternating changes between missing and abundant records from month to month. In the meantime, PS was seen upstream but was never detected downstream. For PS-E, most of the items found in the upstream were either detected in the distributary, or disappeared in the bifurcation; less than 1% was identified downstream. The variation in transport between PS and PS-E may be caused by deposition, extraction, accumulation, or sub-surface transport. Finally, except for PO-hard, the rate of plastic transport was found to be higher near the river banks than in the thalweg. These findings suggest that the transport mechanism of macroplastics in rivers may be more complex than previously assumed, and prompt further studies. Our data allow modelling plastic transport for different plastic categories, designing suitable monitoring or clean-up methods, and understanding the roles of hydrological components such as discharge and flow velocity in transporting plastics.

How to cite: Thi, K., van Emmerik, T., Hoitink, T., and Quy Pham, N.: Plastics Gone Missing: Resolving the Mass Balance at River Bifurcations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1804, https://doi.org/10.5194/egusphere-egu22-1804, 2022.

16:02–16:09
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EGU22-8010
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ECS
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Markus Rolf et al.

Rivers are important transport pathways of microplastics from terrestrial to marine environments. They also interact with terrestrial ecosystems, in particular during flood events, when microplastics can be deposited in or eroded from floodplains. The spatial distribution of these riverine microplastics in alluvial floodplains remains widely unclear. However, the knowledge on their abundance and distribution in floodplain soils is essentially important for ecological risk assessment.

We analysed the distribution of microplastics in three transects of a floodplain soil in a nature reserve in Cologne (Germany). We took soil samples in two different depths (0-5 cm and 5-20 cm), described the soil profiles and plant cover and determined the soil texture. Additionally, we used a hydrodynamic model (MIKE21 software by DHI) and time series of Rhine's water level to analyse the frequency of past flood events from 1950 to 2020. We analysed concentrations of microplastics via ATR-FTIR and µ-FPA-FTIR spectroscopy after density separation and enzymatic-oxidative purification of soil samples. We found elevated microplastic concentrations per kg of dry soil with increasing distance to the river ranging from 25,616 particles/kg to 84,824 particles/kg. Combining the analysis of flood events, the digital terrain model and quantification of microplastics, we show how the local topography (e.g., depressions), flood frequency and soil properties (e.g., grain size) interact and affect the spatial and vertical distribution of microplastics.

How to cite: Rolf, M., Laermanns, H., Kienzler, L., Pohl, C., Möller, J., Laforsch, C., Löder, M. G. J., and Bogner, C.: Interplay of topography, flood frequency and soil properties determine the distribution of microplastics in a Rhine floodplain , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8010, https://doi.org/10.5194/egusphere-egu22-8010, 2022.

16:09–16:16
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EGU22-9118
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ECS
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Highlight
Tim van Emmerik et al.

Land-based plastic waste, carried to the sea through rivers, is considered a main source of marine plastic pollution. However, most plastics that leak into the environment never make it into the ocean. Only a small fraction of plastics that are found in the terrestrial and aquatic compartments of river systems are emitted, and the vast majority can be retained for years, decades, and potentially centuries. In this presentation we introduce the concept of river systems as plastic reservoirs. Under normal conditions, hydrometeorological variables (such as wind, runoff and river discharge) mobilize, transport and deposit plastics within different river compartments (e.g. riverbanks, floodplains, lakes, estuaries). The emptying of these plastic reservoirs primarily occurs under extreme hydrological conditions (e.g. storms, floods). We specifically focus on the retention mechanisms within different river compartments, and their effect on the fate of the plastics that are accumulated over various timescales. With this presentation, we aim to introduce the concept of rivers as (long-term) sinks for plastic pollution, and provide suggestions for future research directions.

How to cite: van Emmerik, T., Mellink, Y., Hauk, R., Waldschläger, K., and Schreyers, L.: Rivers as Plastic Reservoirs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9118, https://doi.org/10.5194/egusphere-egu22-9118, 2022.

16:16–16:23
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EGU22-11219
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Highlight
Charlotte Laufkoetter et al.

Plastic pollution in the natural environment is causing increasing concern at both the local and global scale. Understanding the dispersion of plastic through the environment is of key importance for the effective implementation of preventive measures and cleanup strategies. Over the past few years, various models have been developed to estimate global river plastic export into the oceans, using limited plastic observations in river systems. However, there is a large discrepancy between the amount of plastic being modelled to leave the river systems, and the amount of plastic estimated to be in the ocean.  Here we perform a careful uncertainty analysis of the riverine plastic export estimates, examining both observational uncertainty, model parameter uncertainty, and underlying assumptions in models. Among the quantifiable sources of uncertainty, the conversion of visual plastic observations to plastic mass estimates introduces the largest uncertainty, leading up to three orders of magnitude uncertainty in the final mass estimates in most observations. Model structure and parameter uncertainty add an additional order of magnitude of uncertainty. Additionally, most global models assume that variations in the plastic flux are primarily driven by river discharge. However, we show that within the largest currently available datasets, correlations between river discharge (and other environmental drivers) and the plastic flux are never above 0.5, and strongly vary between catchments. Overall, we conclude that the yearly plastic load in individual rivers as well as the global riverine plastic flow into the ocean may be substantially less well-constrained than indicated by previous studies.

How to cite: Laufkoetter, C., Roebroek, C. T. J., González-Fernández, D., and van Emmerik, T.: The quest for the missing plastics:  Large uncertainties in global river plastic export into the sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11219, https://doi.org/10.5194/egusphere-egu22-11219, 2022.

16:23–16:30
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EGU22-6516
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ECS
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Luca Gallitelli et al.

Plastics represent a new widely distributed global concern, affecting aquatic ecosystems. Macrolitter, with a focus on plastics, can cause detrimental effects on freshwater biota and also affect human health. Among freshwater systems, rivers are of particular interest as they carry the majority of macroplastic litter from the land to the seas. Recently, many studies quantified riverine macroplastic litter transport. Although plastic transport depends on river hydrometeorological factors (e.g. river discharge, wind speed) and geomorphological characteristics (e.g. meanders, river width), several studies highlighted macrolitter accumulation zones in riverbank vegetated areas. However, few studies observed the role of vegetation in entrapping macrolitter on riverbanks. Here, we aimed at quantifying for the first time the plant structure efficiency in macrolitter entrapment. To do so, we sampled riparian areas along 6 rivers in the three riverine zones (upper, middle, lower course) in Central Italy. For each river, riparian vegetation was sampled in relation to river width and riparian zone width. Overall, we found 1,548 macrolitter items on ~300 m2 of sampled riparian areas with plastics representing 96.3% of total litter. Specifically, riparian vegetation entrapped 93.9% of total litter, while 6.1% was found on unvegetated areas of the riverbank. The best efficient riparian plants in entrapping macrolitter were: (i) Populus spp. (51.6%), (ii) Salix spp. (19.0%), (iii) Rubus ulmifolius (6.7%), (iv) Phragmites australis (6.3%), and (v) Ficus carica (1.8%), accounting for 85.4% of the total macrolitter entrapped by plants. Precisely, plants entrapped macrolitter mainly in branches between 0.5 m and 2 m (69.5%) and below 0.5 m (28.3%). Plant structures (e.g. stolons, branches) form a sort of net that can trap litter but can also act as a wall retaining it. The top-5 items entrapped within plants (83.4% of total litter) were: (i) plastic pieces (74.7%), (ii) plastic bags (6.9%), (iii) plastic bendages (6.6%), (iv) sanitary and hygienic towels (4.8%), (v) plastic packaging (4.4%). Among river zones, plants in river lower course entrapped most macrolitter against the upper and middle zones. Some explaining factors for this could be changes in riparian vegetation characteristics and in hydrological regime, as well as higher leakage rate of macrolitter in the lower course of the river. In conclusion, the role of riparian vegetation in entrapping macrolitter is at an early stage, but with high potential to be developed and applied. For the first time, we characterized the role and the structure of riparian vegetation in entrapping macrolitter. We put our emphasis on plant species and structures that are important variables for understanding the entrapment efficiency of macrolitter, highlighting that the complexity of riparian vegetation structure is key for the trapping net effect. As riparian species can provide us the ecosystem service of trapping macrolitter, these findings are crucial for ecosystem restoration and sustainable requalification of the threatened freshwater habitats.

How to cite: Gallitelli, L., Cutini, M., and Scalici, M.: “The net trapping effect”: is riparian vegetation affecting riverine macrolitter distribution?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6516, https://doi.org/10.5194/egusphere-egu22-6516, 2022.

16:30–16:37
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EGU22-8453
Louise Schreyers et al.

Water hyacinths are considered one the world’s most invasive aquatic species and are found in most tropical rivers. Hyacinths can form dense patches of several meters of length and width at the water surface and drift due to the combined action of wind and flow velocity. In rivers, hyacinth patches can function as carriers for floating macroplastic debris from rivers into the ocean. In the Saigon river, Vietnam, water hyacinths were found to accumulate a majority of the total floating macroplastic items (Schreyers et al., 2021). Despite their crucial role in macroplastic accumulation and dispersion, precise quantification of both hyacinth coverage and macroplastic concentrations in rivers are currently lacking. We present insights on the accumulation of macroplastics within hyacinth patches based on the analysis of more than 3,000 Unmanned Aerial Vehicle images collected at the Saigon river in 2021. In particular, we explore the relation between hyacinth coverage, patch abundance and floating macroplastic concentrations, and how these vary through time and space. These findings clearly illustrate the complexity of plastic transport in rivers by highlighting its spatiotemporal variability. Our insights can be used for combined clean-up efforts and reduction strategies of both hyacinths and plastic debris in the Saigon river, and support the development of future plastic monitoring strategies in other tropical river systems.   

References

Schreyers, L., van Emmerik, T., Luan Nguyen, T., Castrop, E., Phung, N.-A., Kieu-Le, T.-C., Strady, E., Biermann, L., van der Ploeg, M. (2021). Plastic plants: Water hyacinths as driver of plastic transport in tropical rivers. Frontiers in Environmental Science 10.3389/fenvs.2021.686334  

 

How to cite: Schreyers, L., Bui, T.-K., van Emmerik, T., Biermann, L., and van der Ploeg, M.: Stuck in vegetation: the role of hyacinths in macroplastic debris accumulation in tropical rivers , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8453, https://doi.org/10.5194/egusphere-egu22-8453, 2022.

16:37–16:40
Discussion

Tue, 24 May, 17:00–18:30

Chairpersons: Tim van Emmerik, Daniel González-Fernández, Marcel Liedermann

17:00–17:03
TB 4 - Transport processes of plastics & Degradation and fragmentation processes & Legislative/regulatory efforts

17:03–17:10
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EGU22-1184
Annie Ockelford and Hazel Beaumont

Microplastic contamination of river sediments has been found to be pervasive at the global scale however, the physical controls governing the storage, remobilization and pathways of transfer in fluvial sediments remain largely unknown. This is particularly so in sand bed rivers where the migration of bedforms has the potential to both store and release any microplastics contained within the sediment bed.  Without detailed experiments to model the movement of microplastics through, and storage within, sand bedforms it is impossible to understand what the environmental legacy of our excessive plastic pollution will be.

We report a series of mobile-bed laboratory flume experiments designed to explicitly quantify the relationship between sand bed surface development and microplastic flux characteristics. Experiments were performed within a glass sided, flow recirculating flume of rectangular cross section (8m x 0.5m x 0.5m). A uniform sand bed (D50 of 450μm) was seeded with either PVC pellets (d=1.4g/cm3), Nylon pellets (d= 1.2 g/cm3), Polycarbonate fragments (d=1.2 g/cm3), Acetal beads (d = 1.4g/cm3) or Nylon fibres (d = 1.15g/cm3). Plastics were mixed into the sediment bed at either 0.1% or 0.5% concentration by mass and sediment beds were exposed to a flow rate of either 0.6 or 0.8 ms-1. Experiments were run until equilibrium conditions were attained as measured by bedform migration rate. During each experiment aerial photographs were taken every 2.5 minutes and videos shot through both the side walls and from top down to track bedform migration and plastic flux. Transported sediment and plastics were captured at the downstream end of the flume in a sediment trap to allow fluxes to be calculated. At the end of each run photographs were taken of the drained bed surface with photogrammetry then used to model the 3D bed surfaces.

Controls on microplastic flux as a result of bed evolution is discussed in terms of both flow rate flow rate and microplastic type.  

How to cite: Ockelford, A. and Beaumont, H.: Controls on microplastic flux during sand bed evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1184, https://doi.org/10.5194/egusphere-egu22-1184, 2022.

17:10–17:17
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EGU22-10288
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Highlight
Marcel Liedermann et al.

Given the longevity of plastics and the yet incalculable effects on the biota in our environment, addressing plastic transport processes in fluvial systems is of emerging importance. Rivers are considered the main entry pathways for plastic into the world's oceans, yet there is still very little research in this area in particular. In Austria, the PlasticFreeDanube project focused on the problem of macroplastics in the Danube. Although Austria has very good waste management, a large amount of plastic still ends up in the national park downstream of Vienna. One of the most important questions in the project was therefore where the plastic comes from, how it is transported in the river and where it is deposited.

 

To improve the process understanding, numerical simulations were carried out on different scales. A particle tracking tool was implemented and adapted to the buoyancy of macroplastic items. The results of the numerical model were then blended with field data to quantify plastic deposition along the shoreline and in the floodplain. Furthermore, field data from GPS tagged plastic items were used for validation of numerical model results and to increase understanding of transport pathways within the system.

 

The modelling results clearly show that floating macroplastic particles interact with hydraulic structures, where the highest accumulation potential was observed in the middle groyne field within row of groynes. The comparison of macroplastic concentrations based on modelling and sampling results shows that floodplains act as filters during flood events. All the macroplastics that were tracked in the field experiment remained on the river’s side on which they were released, indicating that the main input appears to be on the right-hand side. The items mostly stranded on riprap of the bank protection and groyne fields, and the average distance to stranding was found to be 10.4 km. It was also shown that although the Freudenau hydropower plant can retain some of the plastic, a certain amount also passes downstream. The outcomes of this study may lead to a reduction of future collection efforts for macro plastics in riverine environments. The findings can also help to adapt hydraulic engineering structures in a way that facilitates removing more plastic from rivers.

How to cite: Liedermann, M., Pessenlehner, S., Gmeiner, P., Tritthart, M., and Habersack, H.: Analysis of macro plastic transport processes in large rivers using GPS tracking and numerical simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10288, https://doi.org/10.5194/egusphere-egu22-10288, 2022.

17:17–17:24
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EGU22-4450
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ECS
Boaz Kuizenga et al.

Plastics accumulate in the environment due to inadequate waste management, and the durability of the material. A better understanding of fundamental plastic behaviour in the aquatic environment is essential to estimate transport and accumulation, which can be used for monitoring, prevention and reduction strategies. An important process for fate models is the vertical transport of particles, for which the rising and settling velocity are crucial variables. Several studies have described these for microplastics (<0.5 cm) using observations and models. For macroplastics (>0.5 cm) however, such data are scarce. In this study, the rising and settling behaviour of three polymer types (PET, PP, and PE) commonly found in the environment was investigated. The plastic particles were foils of different sizes and shapes. A new method for releasing rising plastics without interfering the flow and disturbing the column was used. Observational data were used to test the performance of four models, including one developed in this study, for estimating the settling and rising velocity based on the properties of the plastic particles. These models were validated using the data obtained in this study, as well as data from another study on plastic rising and settling rates. The newly introduced foil velocity model gave the best results (R² = 0.96 and 0.29 for both data sets, respectively). This model has the potential to estimate the rising and settling velocity of plastic foils, and should be further investigated using additional observational data. The results of our work can be used to further explore the vertical distribution of plastics in rivers, lakes and oceans, which is crucial for improving future efforts to monitor and reduce plastics.

How to cite: Kuizenga, B., van Emmerik, T., Waldschläger, K., and Kooi, M.: Rising and settling velocities of macroplastic foils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4450, https://doi.org/10.5194/egusphere-egu22-4450, 2022.

17:24–17:31
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EGU22-13490
Hassan Elagami et al.

Microplastic (MP) residence times are currently poorly constrained in lakes, especially at a quantitative level. In this work settling experiments with pristine and biofilm-colonized MPs were combined with model calculations to evaluate settling velocities, particle distributions and residence times in the epi- meta and hypolimnion of a hypothetical stratified lake broadly based on Upper Lake Constance. Settling velocities of various biodegradable and non-biodegradable polymers of various shapes, sizes and biofilm colonization were measured in a settling column. The settling velocities ranged between ~ 0.30 and ~50 mm s-1. Particle sizes and polymer densities were identified as primary controls on settling rates. MPs that had been exposed to a lake environment for up to 30 weeks were colonized by a range of biofilms and associated extracellular polymeric substances; surprisingly, however, the settling velocity did not vary significantly between pristine and colonized MP particles. Simulated MP residence times in the model lake varied over a wide range of time scales (10-1 - 105 days) and depended mainly on the size of the particles and depth of the lake layer. Long residence times on the order of 105 days (for 1 µm MPs) imply that for small MP particles there is a high probability that they will be taken up at some stage by lake organisms. It also suggests that insignificant amounts of small MPs will be found in the lake sediment unless some process increases their settling velocity as their residence time is considerably longer than the theoretical retention time of Lake Constance (~4.5 years).

How to cite: Elagami, H., Ahmadi, P., Fleckenstein, J. H., Frei, S., Obst, M., Agarwal, S., and Gilfedder, B. S.: Measuring of microplastics settling velocities and implications for residence times in thermally stratified lakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13490, https://doi.org/10.5194/egusphere-egu22-13490, 2022.

17:31–17:38
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EGU22-8666
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ECS
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Hadeel Al-Zawaidah et al.

Microplastics are an unavoidable part of riverine systems, altering the natural composition of rivers and the associated processes. Within a riverine system, microplastics can be present throughout the water column or within bedload, implying different transport, deposition, and erosion mechanisms. Some recent models have been developed to predict and understand the depth distribution concentration of microplastics and macroplastics, primarily relying on the Rouse model for sediments. However, the great variety in microplastics shape and size accompanied by the dynamic nature of riverine systems (e.g., variety of flow conditions, sediment composition and bedforms) question how realistic and reliable models for plastic distribution along the water column and within sediments are. Present models are often analogous to suspended sediment models and assume diffusivity to be equal to turbulent viscosity, they often exclude the bedload, neglect the effect of turbulence and bed morphology, and come short in explaining the behaviour of mixtures of microplastics and sediments. Understanding these aspects is crucial to improve present models and to aid mitigation efforts and to optimize collection systems and policy. This project targets employing both physical and numerical modelling techniques to further develop depth concentration models of microplastics. We aim to further examine and quantify the influence of turbulence on microplastics transport and concentration distribution by establishing preliminary estimates for the eddy viscosity and diffusivity of microplastics and further examine a wider range of mixtures of microplastics and sediments with different shapes and sizes.

How to cite: Al-Zawaidah, H., Vermeulen, B., and Waldschlager, K.: Microplastic dynamics within turbulence for improved modelling and monitoring strategies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8666, https://doi.org/10.5194/egusphere-egu22-8666, 2022.

17:38–17:45
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EGU22-9603
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ECS
Johanna Schmidtmann and Stefan Peiffer

The pollution of the environment by plastics has become one of the most emerging environmental issues over the past years. Especially micro- and nanosized colloidal particles are of environmental concern since they can be easily taken up by organisms and accumulate in the food chain. Hitherto, only little attention has been paid to the transformation and elimination processes of colloidal microplastic (MP) in the environment. In aquatic environments, colloidal MP will interact with natural constituents, such as metal (oxyhydr)oxides or organic matter. The reaction of those particles is strongly controlled by the surface properties of both, MP particles and the environmental particles. In this study, we investigated the interactions of polystyrene (PS) particles (diameter 1 µm) and ferrihydrite, a common ferric (oxyhydr)oxide. PS particles were allowed to react with ferrihydrite for one week at different pH values (3-11) and constant ionic strength (10 mM). The surface properties of PS were examined before and after reaction with ferrihydrite using dynamic light scattering techniques. Furthermore, we determined the sedimentation rate of PS in presence and absence of ferrihydrite. The results demonstrate that the presence of ferrihydrite increases the sedimentation of PS at all pH values. At neutral pH, we observe not only the strongest sedimentation but also maximum heteroaggregation between PS and ferrihydrite. Overall, our research suggests that ferric (oxyhydr)oxides are highly important reactants to control the environmental behaviour of MP particles. Heteroaggregation with ferric (oxyhydr)oxides and subsequent sedimentation can remove microplastic particles from the water column.

How to cite: Schmidtmann, J. and Peiffer, S.: Heteroaggregation of PS microplastic with ferrihydrite leads to rapid removal of microplastic particles from the water column, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9603, https://doi.org/10.5194/egusphere-egu22-9603, 2022.

17:45–17:52
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EGU22-5567
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ECS
Gilberto Binda and Luca Nizzetto

The interaction of plastics with (trace) elements has recently attracted research interest. Plastic particles, in fact, are contaminating water environments and can possibly act as sinks or vector of (trace) elements affecting their environmental fate and bioavailability.

The details of the mechanisms driving the interaction of plastic particles and (trace) elements are unclear. It has been argued that the degradation processes of polymers and the colonization by micro-organisms can enhance adsorption of (trace) elements. Moreover, the chemistry of water solution is a determinant of the interaction equilibria.

The PLANET project (understanding PLAstic pollutioN effects on the biogeochemical cycle of ElemenTs) aims at elucidating the mechanisms behind plastic - (trace) element interactions and at investigating the implications for the biogeochemical cycle of (trace) elements in water bodies. This aim will be reached through 4 main pillars, consisting in: i) experiments with artificially aged plastics and biofouling experiments, including the characterization of surface physicochemical properties in aged plastics, ii) sorption and desorption tests with ions and metals in batch experiments under varying physicochemical conditions to measure the energy of the interaction; iii) construction of predictive mathematical frames describing this interaction and its impication for (trace) elements’ cycling; iv) assessment of model predictions through microcosms experiments.

The project was launched in November 2021 and currently the first pillar is under development. Tested materials included both polyolefins (PE and PP) and biodegradable materials (PLA and PBAT). Controlled artificial ageing is achieved through UV radiation in water at varying salinity and pH and through inoculation of bacteria and algae consortia into specially designed microcosms. Plastic materials are analyzed through Fourier transform-Infrared spectroscopy to measure changes in surface functional groups, and through scanning electron microscopy to analyze surface morphology. Preliminary results show that biofouling processes take place rapidly under these experimental conditions on different types of polymer (with attachment of first algae in few days). Biofouling has a strong influence on functional groups changes on the polymers: the presence of polysaccharides from bacteria is observable in most of the biofouled plastics. These evidences highlight that a main role in adsorption-desoprtion processes in plastic particles is mediated by the colonizing microorganisms, which can cover an abundant portion of the plastic surface in waters.

How to cite: Binda, G. and Nizzetto, L.: Understanding the effects of plastic pollution on the biogeochemical cycle of elements: introducing PLANET project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5567, https://doi.org/10.5194/egusphere-egu22-5567, 2022.

17:52–17:59
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EGU22-12028
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ECS
|
Highlight
Yvette Mellink et al.

To accurately predict the transport routes of mismanaged plastic waste from land-based sources to their sinks, terrestrial plastic transport models require a robust empirical basis. The main driving forces behind the transport of macroplastics on land are assumed to be gravity, wind, rain and surface runoff. However, the underlying transport principles remain undescribed and unresolved. To determine the minimum wind velocities, rainfall, and surface runoff that are required to mobilize and transport macroplastic items, physical laboratory experiments on an artificial hillslope were performed. Four types of macroplastic waste items were used (bottles, cups, food packaging, and bags) while surface roughness (concrete versus grass) and slope angles (0°, 10°, 20°) were systematically varied. Here we present the identified wind, rain and surface runoff thresholds, as well as the relations between the wind velocity and the plastic transport velocity. These thresholds and relations can be implemented in terrestrial plastic transport models to forecast the transport and (re)distribution of macroplastic waste on land due to wind, rain and surface runoff. The overland pathways simulated by these models, reveal where macroplastic retention occurs on land, and where terrestrial macroplastics enter waterbodies. The locations of the terrestrial accumulation zones, and the main entry points into waterbodies are crucial input for the design of mitigation and prevention measures.

How to cite: Mellink, Y., van Emmerik, T., and Mani, T.: How gravity, wind, rain and surface runoff drive plastic transport on land, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12028, https://doi.org/10.5194/egusphere-egu22-12028, 2022.

17:59–18:06
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EGU22-1768
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ECS
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Highlight
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Nan Wu et al.

Microplastics (MPs) are becoming an important component of suspended particulate matter (SPM), especially in estuaries which are hotspots of MPs pollution. Most SPM in estuarine water are removed via flocculation and further deposited. Therefore, we hypothesise that there is an efficient removal process for MPs by flocculation, which are expected to decrease the overall load of MPs in the marine environment. Here we systematically studied and quantified the influence of MPs properties (size, shape, density, polymer type and weathering condition) on flocculation behavior with suspended sediment in estuary conditions. 

We chose over 20 types of MPs with different properties for 8 size ranges from (10-300 µm for fragments and microbeads, and 10-1000 µm in length for microfibers, respectively). The MPs with different properties and suspended sediment were flocculated in artificial seawater, and the MPs in the system were observed using fluorescence microscopy to distinguish the incorporated MPs and suspended MPs. The incorporation rate (IR) is the ratio of incorporated MPs to total MPs, which is the parameter to evaluate the interaction between MPs and flocs.

The IR decreased with increasing size for fragments and microbeads, and also decreased as the diameter of microfibers rose. The IR for fragments smaller 20 µm is extremely high, from 94.8% to 100%, but gradually decreased with increasing size. For fragments larger than 200 µm, the IR of Polyethylene (PE), Polypropylene (PP) and Polystyrene (PS) are lower than 20%, while higher than 50% for Polyethylene terephthalate (PET) and Polyvinyl chloride (PVC). The IR of PE microbeads is significantly lower than those of fragments. When the diameter of microfibers are smaller than 20 µm, the IRs are always higher than 90%, and the length has no effect on IR. While the IR of microfibers decreased with the length increasing when the diameter of microfibers is larger than 30 µm. According to extensive comparisons between 20 types of MPs, we found that the IR is normally higher in the small size, elongated, angular, high density, weathered, chemically active MPs, while lower in the large size, spherical, low density, pristine and chemically inactive MPs. The size plays the most important role, followed by shape.

There is an evidence that MPs are likely to be removed from the water column and hence estuary sediments are important sinks for MPs. This process reduces overall load to marine environments, but this is selective and depends on the characteristics of MPs. This study offers a reference to predict the preferential removal behavior of MPs in the estuary.

How to cite: Wu, N., Spencer, K., Grieve, S., and Manning, A.: The Estuary as a Natural Water Treatment Plant for Microplastics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1768, https://doi.org/10.5194/egusphere-egu22-1768, 2022.

18:06–18:13
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EGU22-12734
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ECS
Catherine Russell et al.

Rivers are the primary link between terrestrial and ocean environments, crosscutting the landscape whilst providing fresh water, nutrients, and sediment to diverse ecosystems. However, over the past 50 years, rivers have become increasingly significant vectors for plastic pollution. On a riverbed, sediment migrates downstream as bedforms, such as dunes, via well-understood morphodynamic processes, yet the impact of plastic on sediment transport behaviours is unknown and so has been widely assumed as passive, whereby the sediment buries plastic between flood events and is otherwise unaffected. Here we find, through undertaking studies using an experimental recirculating flume tank, that when plastic particles are introduced to riverbed sand dunes, even at relatively low concentrations, novel morphologies and altered morphodynamic processes emerge, including irregular stoss-side erosion and dune wash out. We detail new mechanisms of plastic sequestration and transport to outline how plastic particles interacting with riverbed dunes fundamentally influence sediment transport processes, and the resulting deposits. We find that: i) plastic is not a passive component on riverbeds as it significantly speeds up morphological transformations, affecting bed topography and increasing dune erosion rates, which at present has unknown consequences for the wider landscape; ii) plastic inclusion locally changes the ratio of suspended load to bedload material as plastics create a local and temporal shift towards more sediment in suspension, thereby causing the river to develop more conduit-like than storage-like properties with unknown consequences for overall sediment transport fluxes and increased local turbidity; and iii) inclusion of plastic in the sediment layer creates heterogeneous deposits that propagates the disruption of sedimentary processes and forms irregular distribution of plastic on the riverbed that will affect the possibilities of representative sampling. Such insights shed light onto a new branch of environmental consequences of plastic in the environment that requires further research, as a new branch of sedimentology: plastic and sediment interactions. With plastic being continually added to our environments globally, this new field is set to be increasingly relevant amongst emerging challenges of the Anthropocene.

How to cite: Russell, C., Fernández, R., Parsons, D., and Gabbott, S.: Plastic pollution impacts riverbed sand transport processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12734, https://doi.org/10.5194/egusphere-egu22-12734, 2022.

18:13–18:20
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EGU22-4239
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ECS
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Jagoda Worek et al.

At the end of the 1940s, the production of plastics began on a large scale. Since then, a dynamic increase in their production has been observed. It is associated with a variety of applications and low costs. The negative consequences of the use of polymers and poor disposal are still growing. Microplastic is an important hazard. These are pieces of plastic, the size of which does not exceed 5 mm. Microplastic particles have already been detected all over the world. Increasingly, attention is being paid to their accumulation in the environment. During their stay in ecosystems, they undergo aging processes. Their structure and composition are changing. The washed substances are released into the environment. The aim of the research was to check the effect of artificial aging methods on the leaching of functional groups and changes in the structure of selected polymers. Polystyrene and polyethylene terephthalate were selected for the research. They belong to the most common kind of plastics. For aging, combined methods were used, with irradiation with UV lamp irradiation and hydrogen peroxide. Before and post-aging polymers were analyzed using spectroscopic methods and a microscope. ATR FTIR, Raman confocal microscope and FTIR microscope were used for this purpose. The tests showed leaching of organic products from the samples and the formation of additional  bands. The structure of plastics has changed. These changes show a possible degradation path for plastics with a significant environmental impact.

How to cite: Worek, J., Styszko, K., and Białas, A.: Influence of chemical aging processes on releasing organic products from microplastics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4239, https://doi.org/10.5194/egusphere-egu22-4239, 2022.

18:20–18:27
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EGU22-928
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ECS
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Paul Vriend et al.

Macroplastic pollution in and around rivers negatively impacts human livelihood, and aquatic ecosystems. Monitoring data are crucial for better understanding and quantifying this problem, and for the design of effective intervention strategies. However, current monitoring efforts are often short duration, or study single river compartments. We present a ‘Roadmap’ to overcome the challenges related to the design and implementation of long-term riverine macroplastic monitoring strategies. This ‘Roadmap’ can help accelerating the process of achieving structural monitoring through providing a stepwise approach, which links monitoring goals and research questions to the data and methods required to answer them. We identify four monitoring goals: (1) policy, (2) knowledge development, (3) operations, and (4) solutions. Linked to these, we provide a non-exhaustive list of 12 globally common research questions that are important to answer to reach these goals. The ‘Roadmap’ takes these questions and links them to development levels of monitoring methods for each river compartment: (1) method development, (2) baseline assessment, and (3) long-term monitoring. At each level, specific questions can only be answered if the level is achieved for specific river compartments. For questions at higher levels, the previous levels need to be achieved first. This creates a clear stepwise approach to solve open challenges. With the ‘Roadmap’, we provide a new tool to support decision-making and planning of specific projects by policy makers. The ‘Roadmap’ is a clear and stepwise, yet flexible framework that allows to add and remove elements based on new insights, available resources, and other relevant changes.

How to cite: Vriend, P., van Emmerik, T., and Copius Peereboom, E.: Roadmap for long-term macroplastic monitoring in rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-928, https://doi.org/10.5194/egusphere-egu22-928, 2022.

18:27–18:30
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