Plastic is considered one of the most practical inventions of the 20^th century, providing us with a range of very practical materials. However, due to mismanaged waste the plastic pollution has become persistent in aquatic environments. As the plastic products undergo environmental weathering once released in the aquatic environment, they degrade and are fragmented into a highly heterogeneous group of particles with different sizes (i.e., from centimeter over millimeter and micrometer to nanometer scale), shapes, densities, and chemical compositions. However, due to the lack of suitable analytical methodology, knowledge on degradation and/or fragmentation of plastics to nanoplastics (NPs, 1-1000nm), especially in the aquatic environments is still largely lacking.

In the framework of the MS4Plastics project, 15 different plastic materials, including a surgical face mask, different polymer pellets, rubber dust, and plastic powders as common examples of plastics expected to be present in the aquatic system were added to  Milli Q water and exposed to UV-light for 120 hours to better understand plastic degradation and/or fragmentation into NPs. Finally, for detection and size determination of NPs formed after accelerated UV-driven plastic fragmentation in water, dynamic light scattering was used. For a fraction of the samples, asymmetric flow field-flow fractionation (AF4) hyphenated to multi-angle light scattering (MALS) was used as a complementary analytical technique for characterization of NPs.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 101023205.

How to cite: Velimirovic, M., Dumont, G., De Wit, J., Tirez, K., Voorspoels, S., and Vanhaecke, F.: UV-driven fragmentation of plastics in an aquatic environment: laboratory studies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-72, https://doi.org/10.5194/egusphere-egu23-72, 2023.

Easily transportable microplastics (plastic particles < 5 mm) have become an increasingly important component of suspended particulate matter (SPM) in the aquatic environment, and their fate is significantly influenced by aggregation and flocculation. Aggregation modifies particle properties (e.g., size) controlling the hydrodynamics of SPM in the aquatic environment. Hence, understanding and quantifying aggregation is key to predicting the behaviour of both SPM and associated microplastics. However, quantifying the aggregation degree of microplastics with complex parameters in various water environments is very difficult.

Here, an extensive range of microplastics including 8 polymer types, 3 shapes, different weathering conditions and different sizes (10-300 µm for fragments and microbeads, and 10-1500 µm in length for microfibers, respectively), were used to explore the aggregation dynamics of microplastics. Over 4000 measurements of incorporated microplastics were collected, and we found microplastic size (MinFeret diameter of fragments, diameter of microfibers) is the key parameter to determining the aggregation behavior. Our results simplified the aggregation of microplastics with a wide range of properties in various water ecosystems into two parameters, the size of microplastics and the size of aggregates. A boundary curve for microplastics was fitted based on size relationships between microplastics and aggregates to divide microplastics into aggregable and un-aggregable groups. This study can aid better understanding the fate of microplastics in various aquatic environments at multiple scales.

How to cite: Wu, N., Grieve, S., Manning, A., and Spencer, K.: Aquatic Aggregates as “Vector” for Microplastics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14433, https://doi.org/10.5194/egusphere-egu23-14433, 2023.

Plastics are a well-known problem that accumulates in the environment causing detrimental effects on ecosystems. Macroplastics in rivers are only recently studied, with most studies focusing on the transport of plastics to the sea. However, most plastics are retained in the fluvial system. To date, only abiotic factors have been considered in the transport process, but recently vegetation has proven to block plastics from having a pivotal role in influencing plastic riverine drift. Given that little is known on the biotic component affecting riverine plastic transport, we aimed at investigating further on (i) the three-dimensionality structure of riparian vegetation in trapping plastics along watercourses and (ii) to develop a vegetation index to describe vegetation structure and to understand the plastic entrapment service provided by plants. To do so, we sampled field data from central Italy rivers along the three riverine zones considering riparian vegetation in relation to river width. Data on plastics within vegetation has been recollected. Also, data on plant structures (i.e. the number of individuals and the number and height of branches per species) was sampled and then used to develop the 3D vegetation index (i.e. 3D Vegetation Index, 3DVI) considering the tridimensionality and diversity index. As result, plastics occurring in vegetation were significantly related to vegetation structure with the 3DVI correlated with the number of plastics (R² = 0.36, p = 0.0086, Y = 0.007157*X + 2.562). Furthermore, the most dense and diverse community block more plastics. Considering different vegetation heights in all the rivers, there is a significant linear regression between the 3DVI in vegetation branches (0.5<r<2.0 m, and r>2.0 m, respectively R² = 0.38, p = 0.007, Y = 0.007662*X + 2.711 and R² = 0.45, p = 0.0023, Y = 0.2522*X + 2.696). With regards to the three riverine zones, only in the lower river zone there was a significant regression between 3DVI and plastics in vegetation (R² = 0.94, p = 0.001, Y = 108.0*X-143.7). Biotic factors (i.e. vegetation structure) most correlate to the occurrence of plastics in vegetation driving the plastic entrapment process more than the environmental abiotic factors (i.e. hydrology). Overall, we developed for the first time a vegetation index to describe the structure and diversity of the plant community related to the plastic entrapment service. The higher the 3DVI value, the more complex the vegetation (i.e. characterised by a lot of individuals and branches). We emphasized that plant structures are important variables for understanding the entrapment efficiency of macrolitter, highlighting that the complexity of vegetation structure is key for the trapping net effect. As vegetation retain plastics efficiently in all the zones providing us the ecosystem service of trapping macrolitter, the 3DVI could be applied for future solution to plastic pollution – also detecting plastic hotspot areas for mitigation and clean-up activities.

How to cite: Gallitelli, L., Cutini, M., and Scalici, M.: Lost in the river: the plastic vegetation index for detecting plastics within vegetation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12840, https://doi.org/10.5194/egusphere-egu23-12840, 2023.

The widespread use of plastic has made it a widely dispersed product with a high impact on the environment. Through fragmentation of larger pieces or direct discharge, microplastic particles (MP) are present in almost every aquatic ecosystem. MPs based on polymers of lower density than water (ρ < 1.0 g cm⁻³), such as polyethylene (PE), are among the MPs most commonly found in the sediments of freshwater systems which is counterintuitive. Different mechanisms and theories may explain the dynamics of buoyant positive MP motion and their deposition in water systems. Thus, examining the behavior of MP particles carried in suspension is particularly relevant to assess this contaminant fate. The experimental approach is an important way to help to fill the knowledge gap exist on the transport of these particles in natural flows. In this study, Particle Image Velocimetry (PIV) has been deployed to investigate how turbulent water regime contribute affect the dynamics of buoyant particles and if it drives them towards the bed . Different sets of experiments with different flow velocities and non-cohesive bed types were conducted in a 200 cm long, 30 cm wide, 22 cm deep, rectangular, re-circulating, tilting flume. The PIV measurements were done in the centerline of the flume. A camera framed and recorded images in the laser sheet at 15 Hz to follow fast turbulence fluctuations. Pristine PE particles of around 47µm were used. A particle tracking technique was used to record, to follow the trajectory and to calculate de velocity of the particles. The analyzed images clearly show that turbulence homogenizes the particles in the water column. Also, a substantial quantities of PE particles were subject to downward vertical transport which in its turn increase the chance of particles coming in contact with the bed. Turbulent energy is an important driver in the dynamics of buoyant positive particles, and under more realistic environmental conditions, as biofilm presence on the sediment, would enlighten the trapping of these particles by the sediment.

How to cite: Molazadeh, M., Calabro, G., Liu, F., Dris, R., Chaumont, C., Rovelli, L., Lorke, A., Lemaire, B. J., Gasperi, J., Tassin, B., and Vollersten, J.: Visualization of Buoyant MP motion in response to different flow velocities and bed types, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12960, https://doi.org/10.5194/egusphere-egu23-12960, 2023.

The transport of plastic in rivers is affected by a wide variety of factors, such as river discharge, wind drag, and tides. These dynamic processes include the travelling time or distance, retention time or location, and remobilization rate of plastic items, which can be quantified by using GPS-based trackers. However, these properties are still unknown in some specific locations, including river bifurcations where the changes in river discharge, flow velocity, and river morphology are significant. Here, we demonstrate the behaviour of plastic transport in a river bifurcation area not influenced by tides during flood season in the Red River system of Vietnam. While all trackers retained somewhere in the river after hours or days, we found that after 10.5 kilometers downstream of the bifurcation, 9 out of 10 trackers followed the main channel retained in the same approximately 6-kilometer-long river segment. Meanwhile, 50% of the 6 trackers that left the main channel to enter the tributary also retained in the same 2.5-kilometer-long river segment 9 kilometers downstream of the bifurcation. These findings are linked to the concept of rivers as plastic reservoirs, as none of the trackers that stranded on the riverbanks for several days was remobilized. Furthermore, the retention of trackers in the same area after leaving the bifurcation clearly indicates shared driving factors on plastic transport, which are likely the river discharge, wind direction or velocity, and river morphology. Our results underscore the need for future research on delineating exact accumulation zones of the plastics in riverbanks considering the effects of wind, river discharge, and river morphology.

How to cite: Thi, K., van Emmerik, T., Hoitink, T., Vermeulen, B., and Pham Quy, N.: Plastic transport and retention around river bifurcations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15187, https://doi.org/10.5194/egusphere-egu23-15187, 2023.

Kimitsuki et al (SIL 2022; EGU 2023, this session) have reported near-surface microplastic particle concentrations from 26 quasi-monthly sampling dates over three years in Lake Biwa, Japan.  The concentrations show a high degree of intermittency, both in the shallow South Basin and the deep North Basin.  Kimitsuki et al have suggested that the dates of high particle concentrations followed relatively strong wind events, which are hypothesized to stir up bottom sediments together with deposited microplastic particles. In the South Basin, which has an average depth of 4 m, this hypothesis seems very natural.  However the sampling point in the North Basin was located in waters well exceeding 60 m depth.  If the sampled microplastic particles there originated from wind-induced resuspension events, it seems likely that the resuspension occurred at shallower bottom depths close to shore.

Through well-resolved hydrodynamic simulations, combined with particle tracking, the current work considers how resuspension at shallow depths, followed by advection during the days preceding sampling, might explain the two highest spikes in Kimitsuki et al’s sampled concentrations in the North Basin.  These spikes occurred on June 20, 2021 and July 4, 2021, when measured particle concentrations were respectively 54 and 46 particles/m³, as may be compared to the median value over the three-year campaign of 6.5 particles/m³.  Preceding both dates, both forward and time-reversed particle tracking suggest that the sampled microplastic particles could have been resuspended from the lakebed at depths of around 10 meters, near to the shore about 5 km northwest of the sampling point. At this location and depth, internal waves, associated with vertical undulations of the thermocline, were predicted to induce strong water currents near the lake bottom.  The simulated near-surface currents were then predicted to transport such resuspended particles offshore toward the sampling location.

How to cite: Wells, J. C.: On the hypothesis of microplastics resuspension by internal waves in a deep stratified lake., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14971, https://doi.org/10.5194/egusphere-egu23-14971, 2023.

Managed Aquifer Recharge (MAR) belong to the nature-based engineering approaches poised to play an increasingly positive role in climate change adaptation. In fact, the increased groundwater availability thank to MAR can buffer future temporal water shortages driven by forecast longer droughts. However, one concern of MAR regards the quality of the infiltrating water as it affects groundwater quality.

There is growing concern about groundwater contamination by microplastics (MP) delivered by the infiltrated surface water. Indeed, MPs have been found in rivers globally. Groundwater contamination by MPs could then have direct detrimental consequences on groundwater management and availability for human uses.

In this study, we measured MPs larger than 20 µm in the different important stages of a major MAR-water supply system in Switzerland. The MAR system has been diverting an average of 95,000 m³/day of Rhine water through channels and ponds since 1958. Samples of filtered water were taken in triplicates from the Rhine River near Basel, the treatment stages before the managed infiltration outlets, the pumped groundwater, before and after the activated carbon filters. The methodology involved the analysis of the filters by means of micro-Fourier Transform InfraRed (FTIR) spectroscopy and MPs identification by means of the machine-learning model developed by the Purency company. The possible contamination by MPs smaller than 20 µm could not be assessed due to practical challenges for water filtration in the field and quantification (reliable micro-FTIR measurements down to 20 µm). Before analyses, we added surrogate particles of polyethylene with an average size of 60 µm for quality assurance and quality control.

The measurements revealed satisfactory MPs reduction along the MAR system. While the number of MPs in the raw Rhine River had to be quantified still, MPs average concentration decreased from about 9.75 particles/l in the treatment stage to about 1.3 particle/l after the activated carbon filter. MPs average concentration increased to 7 particles/l between the pumped groundwater and the activated carbon filters. The increase was driven by a high count of polypropilene MPs in one of the triplicates. Our study could not exclude a possible MPs contamination by construction materials used in the facility. The measured concentrations referred to a randomised scan of about 50% of the area of the filters encompassing the centre and the edges of the filters. Most of the surrogate particles accumulated along the edges. Yet, we only considered particles with a value of the Relevance and Similarity metrics greater than 0.3.

Acknowledgements: We thank our colleague Reto Britt who supported with the sampling campaign and laboratory measurements and the drinking water supplier for allowing us to carry out the study within their premises.

How to cite: la Cecilia, D., Moeck, C., Kägi, R., Philipp, M., and Schirmer, M.: Microplastics transport during Managed Aquifer Recharge – A potential cause of groundwater contamination?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16732, https://doi.org/10.5194/egusphere-egu23-16732, 2023.

The increasing recognition that significant amounts of plastic are disposed of and accumulating in agricultural soils has highlighted the need for increased research in the study area.  Once on soils, MP may be transported through vertical migration and/ or overland surface runoff, with processes governing the overland runoff pathway to freshwater systems being poorly understand.   Here we present a study of MP transport from soils through overland flow processes.  The research utilised a medium-scale, laboratory based, rainfall simulator that facilitated experimental testing of multiple variables that influence MP mobilisation and export from field settings under controlled conditions.  A total of 15 experiments were conducted across four separate test series in which differences in MP characteristics (including particle shape, size and density), rainfall regime (including intensity and duration), catchment topography (slope), time lag between MP seeding in the soil surface and rainfall event, together with the catchment condition in the progression of a growing cycle (bare soil to grassland), were tested to capture an extensive and realistic set of MP and environmental test conditions.

Each test followed an identical procedure to ensure consistency across all test series. For each test, a soil sample (particle size distribution of 21.1%, 40.9% and 37.8% clays, silts and sands, respectively) was prepared in a free draining test box (measuring 3.3 x 1.2 x 0.1 m (length x width x depth)) and compacted to achieve a soil bulk density of 1.36 ± 0.2 g/cm³, a value typical for soils in standard agricultural settings.  MP were then seeded in the soil surface with the soil sample being exposed to the test rainfall regime. MP in runoff samples, collected every ten-minutes from a single point drainage system mounted on the test box, were filtered and dried, microscopically and manually separated into their three polymer groups (PP, HDPE and PVC). Mean size for each polymer was recorded as was the overall MP mass in each sample.

Among all parameters examined in this study, rainfall intensity was observed to be one of the most influential in exporting MP from the test catchments.  However, a statically significant difference was not observed when comparing MP export and the timing of a rainfall event following MP seeding.  Increasing catchment slope was also shown to be driver of MP transport in overland runoff with values being higher for bare (simulating recently tilled conditions) soils as opposed to soils with grass swards. Smaller MP particles were shown to be more mobile across all experiments, with larger particles only increasing in mobility with an increase in rainfall intensity. Average MP size in collected samples for low intensity rainfall events (8.4 mm/h) was 0.89 mm, 0.63 mm and 1.67 mm for PP, HDPE, and PVC respectively, increasing to 1.15 mm, 0.89 mm and 1.74 mm for the same polymers during the high intensity event (18 mm/h). Increases in MP mobility were shown to be shape specific, with the strongest correlations noted for PP and HDPE, while no significant correlation was found for PVC particles.

How to cite: O'Sullivan, J., Bruen, M., Heerey, L., Mahon, A., Lally, H., Murphy, S., O'Connor, J., O'Connor, I., and Nash, R.: Understanding the overland transport of microplastics from agricultural soils to freshwater systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10261, https://doi.org/10.5194/egusphere-egu23-10261, 2023.

To date, we know little about depth-resolved distributional patterns of microplastic particles (<630 µm) of streambed sediments. Reports in literature about the abundance of considerable amounts of microplastic particles in fluvial sediments indicate that the transport follows naturally occurring flow vectors into streambed sediments. We hypothesize, that locally occurring hydraulic conditions at the water-sediment interface which are characteristic for various naturally occurring riverbed morphological structures might influence the evolution of microplastic depth profiles.

As a first step of identifying morphologic feature specific microplastic depth profiles, we have carried out a series of six freeze core sampling campaigns at the centre of the longitudinal axis of two riffles located in a fourth order gravelbed river (Ruwer) contributing to the Moselle River in Trier, West Germany. The setup allows for sampling a 50 cm long undisturbed sediment freeze-core. Using dry ice as coolant and a diamond saw blade we obtained ten undisturbed sediment cube samples (125 ccm) cut from the vertical axis up to 50 cm depth from each freeze-core. Over the range from 5000 – 25 μm five size fractions were analysed with regard to mineralic sediment and microplastic particle distribution. In all sediment cube samples microplastic particles and fibres could be detected without showing distinct distributional patterns related to its depth. Although the samples represent only a small surface area (25 sq. cm), we could qualify and quantify 81 microplastic items plus 606 suspected items mainly composed of transparent fibres using Raman microspectroscopy. Furthermore, we observe an exponentially increase in microplastic abundance with decreasing size fraction by three orders of magnitude. Dominant plastic types are polypropylene, polyethylene, nitrile and polyether terephthalate representing 85% of our findings. Our first results imply that in riffle heads downward directed transport within the sediment layer affects rather the shape and size of the plastic than the absolute abundance. As a next step, typical depth patterns of microplastic at the upstream and downstream end of streambed riffles have to be identified.

How to cite: Utecht, S. and Schuetz, T.: A depth-resolved snapshot of microplastic abundances in riffle heads in a gravelbed river, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-673, https://doi.org/10.5194/egusphere-egu23-673, 2023.

Riverine macroplastic pollution (>0.5 cm) negatively impacts ecosystems and human livelihoods. Monitoring data are crucial for understanding this issue and designing effective interventions. Macroplastic pollution floating on the river surface and plastic deposited on riverbanks are studied relatively often. Data on riverine plastics in the water column remain scarce. In this study we utilize trawl nets at different depths to sample plastic pollution in the water column at the entry point of the river Rhine to the Netherlands. We show that plastic concentrations in the water column increased during higher discharge. The combination of higher macroplastic concentrations and higher discharge leads to considerably higher plastic transport during high discharge events. Moreover, the results indicate that the vertical distribution of macroplastic pollution changes during different flow conditions. Significantly higher concentrations of macroplastic can be seen near the riverbed during low discharge conditions, while no significant differences in concentration are observed between the bottom, middle and surface samples during high discharge conditions. These findings provide first insights into the key role of hydrology in explaining macroplastic transport in the water column. These insights can be used to improve future monitoring and intervention strategies. 

How to cite: Vriend, P., Schoor, M., Rus, M., Oswald, S. B., and Collas, F. P. L.: Macroplastic concentrations in the water column of rivers increase with higher discharge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7893, https://doi.org/10.5194/egusphere-egu23-7893, 2023.

Globally, fluxes of microplastics to marine environments are thought to be dominated by stormflow from urban environments, which may be moderated by storage in estuaries. Fluvial transport of microplastics is primarily a supply-limited phenomenon, but flow field and particle characteristics can result in a wide range of transport modes, from surface load to bedload, with potential ramifications for estuarine transport and fate. Here we report preliminary findings from microplastic monitoring campaigns conducted in a number of streams draining urban watersheds in Southern California, and estuarine wetland and benthic sediment deposits. These studies will serve as the basis for microplastic flux, accretion, and composition evaluation, and inform the optimization of microplastic monitoring in urban systems.

How to cite: Gray, A., Cowger, W., Singh, S., and Murphy-Hagan, C.: Microplastics in Urban Watersheds, Southern California, USA, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16958, https://doi.org/10.5194/egusphere-egu23-16958, 2023.

Mismanaged plastic waste continually accumulates in the marine environment. A large amount of its emission to the ocean originates on land and is transported by rivers, streams and artificial drains. However, monitoring efforts and knowledge building on the dynamics and quantification of these emissions based on field research is scarce and subject to local catchment scale.

Here, we present an experimental study of plastic waste transport and retention dynamics in artificial drains (gullies) subject to flash floodings in short drainage areas of Kingston, Jamaica. We developed a novel plastic waste piles survey using UAV and field measurements. The offered investigation has the potential for estimation of plastic waste piles (i) volumes and composition, (ii) transport-retention-remobilization cycles and (iii) correlation with local hydro-meteorology, especially during peak events, where most of the plastic waste is transported.

Until now, monitoring efforts were carried out on the lower stretch (1km) of three gullies flowing to Kingston Harbour and the Caribbean Sea during 90 days in the hurricane season of 2021 on a bi-weekly basis. The current dataset includes 24 orthorectified images of the gullies and plastic waste piles. Direct samples of the plastic waste piles are being collected for ground-truth validation. We observe that plastic waste piles are more prominent when large objects (such as refrigerators, tree branches or tyres) are present, forming a base for greater accumulation and affecting remobilization cycles.

These results are essential for understanding macroplastic transport processes and the development of innovative technological solutions preventing plastics inflow into the ocean. It has the potential to provide insights into the operational performance before and after the implementation of interception solutions or mitigation measures. Furthermore, it serves as baseline data to strengthen local policy-making on initiatives assessing harmful effects in surrounding ecosystems.

How to cite: Correia, R., Assumpção, T., Buchanan, L., Fletcher, D., and Maxam, A.: Understanding plastic waste dynamics, correlations with hydrological extremes and its contributions to the development of innovative interception and mitigation solutions within Kingston Harbour, Jamaica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14632, https://doi.org/10.5194/egusphere-egu23-14632, 2023.

Standardized sampling methods and protocols are essential to facilitate the comparison of studies on plastic pollution and to advance knowledge of this environmental issue. Several protocols for sampling microplastics in oceanic and coastal waters have been developed, compared and even harmonized for this purpose. However, these protocols may be not adapted for the study of estuarine environments, characterized by strong vertical, horizontal and temporal gradients.  In this work, microplastic sampling methods and strategies are discussed in relation to estuarine hydrodynamic processes. The analogies between the dynamical behaviour of microplastics and sediments make it possible to draw out recommendations for sampling microplastics based on several decades of research in estuarine hydro-sedimentary dynamics. In particular, we will discuss when, where, and how to sample microplastics in order to capture the most representative picture of microplastic pollution in these highly dynamic systems subject to strong anthropogenic pressures.  

How to cite: Defontaine, S. and Jalon-Rojas, I.: Sampling microplastics in estuarine environments: lessons learned from suspended sediment dynamics and perspectives., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8819, https://doi.org/10.5194/egusphere-egu23-8819, 2023.

Over the last years macroplastic has been increasingly monitored not only in oceans but also in freshwaters. Despite the ongoing discussion of linking plastic masses in rivers with masses in oceans, multiple studies showed a highly complex transport of plastic debris from in land-based sources towards the oceans. However, current modeling and monitoring studies mostly focused on specific processes in single rivers or used highly simplified approaches. While such studies may be helpful to identify the fate mechanisms, they are less suitable to predict macroplastic flows in a large river network on country-scale. The aim of our work was therefore to develop a macroplastic fate model for a whole country which was parameterized based on measurements in specific rivers. For the macroplastic modelling we considered four different states: (1) in suspension, (2) temporally stored (3) long term burial or accumulated and (4) removal / cleaning from in suspension or temporally stored masses. The model considers a high spatial resolution with river sections of few meters to kilometers in length which are connected to the overall river network. As input data we used macroplastic emissions predicted by a material flow analysis model on the same spatial resolution. The model was applied before to predict macroplastic masses on a river level.

Using our model we found that the considered transport and fate processes for macroplastics must clearly differ from processes considered for microplastics. As possible influencing fate and transport factors we compared the influence of parameters such as sinuosity of rivers, the land use in close river distance, the discharge or impact of weirs with macroplastic removals. Each parameter was identified by other studies as potential factor for macroplastic retention. Here, we explore their influence on the output on a country-scale. We conclude that based on our modelling a high retention of macroplastics must occur within the system to match monitoring data with predicted macroplastic releases. While we assume that high amounts of macroplastics will be temporally stored until the next flooding event, it remains challenging to predict the long term in-situ accumulation. As a first step, we simulated different parameter settings to mimic "normal" discharge conditions in comparison with flooding events.

Overall our results bring existing concepts and understanding in a wider context by coupling emission modelling with fate modeling and monitoring results from literature. Moreover, we are able to predict macroplastic masses in rivers and temporally stored in river banks and compare predicted values with first available measurements. Especially, predicting microplastic masses is of high importance for policy makers to manage plastic pollutions along riversides.

How to cite: Mennekes, D., Mellink, Y., van Emmerik, T., and Nowack, B.: Exploring Macroplastic Transport and Retention Dynamics in Country-Wide River Networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1182, https://doi.org/10.5194/egusphere-egu23-1182, 2023.

Suspended plastic transport is one of the big unknowns in present plastic research. It is either neglected or measured using expensive and labour-intensive underwater net-measurements. In search for additional measurement methods, the Acoustic Doppler Current Profiler (ADCP) has recently been explored as a tool for detecting plastic debris. ADCPs emit a high-frequency acoustic signal, which is scattered back to the transducer by particles in the water column. The frequency shift and the strength of the returned signal (backscatter) are used for respectively flow velocity and suspended sediment concentration estimates. Large objects like fish and organic material can be recognised in the acoustic signal by a strong local increase in backscatter. It has been shown that ADCPs can also detect plastic debris during controlled tests. The characteristics of the acoustic signal of plastics in an uncontrolled setup under varying conditions is still understudied.

To develop knowledge on in situ plastic detection, we first deployed an ADCP in a small flowing system into which we introduced plastic litter varying in size, composition and shape. Secondly, a test was undertaken with a simultaneous ADCP and net measurement in a large Dutch river. The uncontrolled plastic transport of the river is estimated based on ADCP data, and calibrated and validated using the net measurement. The tests gave novel insight into the signature of flowing plastics in the backscatter signal, and the present possibilities and challenges of in situ plastic detection using ADCPs. Overall, plastic detection using ADCPs has the potential to provide valuable information about the spatial and temporal variability of suspended macroplastic transport in rivers, aiding efforts to mitigate the negative impacts of plastic pollution. More research is needed to create a complete overview of backscatter characteristics of litter and to develop effective automated algorithms and methods for accurately distinguishing plastic.

How to cite: Boon, A., van Emmerik, T., and Vermeulen, B.: Detection of suspended macroplastics in the field using acoustic backscatter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13885, https://doi.org/10.5194/egusphere-egu23-13885, 2023.

Plastic pollution of water bodies is a major environmental issue, as it can have harmful effects on marine life, riverine ecosystems and society as a whole. To mitigate the impacts of plastic pollution, accurate detection and quantification of macroplastic litter (plastic items > 5 mm) is of particular importance. In recent years, researchers and engineers have developed Deep Learning methods showing promising performances for detecting riverine macroplastic litter. However, there are several outstanding issues hindering the advancement of the field, including the lack of available data sources for training such models.

Here, we present a new open source dataset for the detection of floating macroplastic litter. We generated the dataset from controlled experiments carried out in a small drainage canal on the TU Delft campus. The dataset features 626 different litter items including plastic bottles, bags and other plastic objects, as well as metal tins and paper litter. These items include household waste as well as litter recovered from canals in the Netherlands. We captured images with a resolution of 1080p and a linear field of view using two different action cameras and a phone, mounted on a bridge. The dataset consists of 10000 images, taken from two different heights (2.7 and 4.0 meters), two different inclinations (0 and 45 degrees from the horizontal), and two different weather conditions (sunny and cloudy sky).

In this presentation, we provide information on the dataset and the experiments carried out to generate it. We also discuss the results of benchmark Deep Learning models for multi-class classification trained on the dataset, and their out-of-sample generalization ability to other case studies. While labels are currently available only for image classification, we aim to release annotations for object detection and image segmentation tasks in the future.

How to cite: Vallendar, A., Jia, T., de Vries, R., Kapelan, Z., and Taormina, R.: An open source dataset for Deep Learning-based visual detection of floating macroplastic litter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12092, https://doi.org/10.5194/egusphere-egu23-12092, 2023.

Rivers and estuaries are a key transport pathway for plastics from inland to the sea. These systems are subject to fluctuations depending on sources of plastics and local environmental factors, causing variation in the plastic concentration up to several orders of magnitude within limited time ranges. Due to this large variability, in freshwater systems, it is challenging to obtain representative monitoring data. This study presents a new methodological approach to determine the number of plastic particles needed to obtain representative data for plastic pollution characterization in estuarine waters. The method used monthly in situ observations during a period of two years in the Guadalquivir River estuary (SW Spain). The data allowed the characterization of plastic concentrations across all size categories (micro-, meso- and macroplastics). The items were categorized into different size classes (<5 mm, 5-25 mm, 2.5-5 cm, 5-10 cm and >10 cm) and a resampling simulation was applied to generate 95% confidence intervals for plastic concentration variability. Our results suggest that, when using a limited number of samples, there is an underestimation of all size classes, e.g., up to three quarters of the samples could underestimate the average number of particles. Differences up to 3 orders of magnitude can be established between the lower (<5 mm) and the higher (>10 cm) size class in terms of number of particles sampled. This approach will help to optimize time and define sample size for specific particle size classes to improve plastic monitoring in freshwater environments.

How to cite: Quintana Sepúlveda, R., González-Fernández, D., Cózar, A., Manzano-Medina, S., Pérez-López, L., and Morales-Caselles, C.: A new methodological approach for the assessment of plastic pollution in estuarine waters: Guadalquivir River (SW Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14841, https://doi.org/10.5194/egusphere-egu23-14841, 2023.

Rivers transport, and store a large share of the global plastic pollution. Riverbanks are one of the river compartments where macroplastic litter is deposited and retained. Different factors influence macroplastic deposition on riverbanks. Retention related factors such as riverbank features, and supply related factors, such as hydrometeorology or land-use. Riverbank macrolitter along the Dutch Meuse has been quantified, characterized, and removed biannually since 2017. At each monitored riverbank, macroplastic and other litter items were collected along a 100 m section and classified in over 100 specific litter categories. We assume that after each monitoring round all litter is removed, and that the litter sampled in the following round has accumulated in the time between rounds. This monitoring dataset is analyzed to identify riverbanks with plastic accumulation rates continuously below or above average, and the specific characteristics of these identified riverbanks. Furthermore, correlations are investigated between macroplastic deposition and individual riverbank features and river morphology, such as types of riparian vegetation, or curvature of the river. These correlations are tested for the total amount of plastic litter, but also categories grouped by plastic characteristics such as potential source, density, size, or flexibility. This is done based on the hypothesis that plastic litter items with different characteristics are associated to different processes of plastic emission and deposition. For example, items with low or high density, or different levels of flexibility. Items with low and high densities are transported differently, because their density is lower or higher than the density of water. Items with a high level of flexibility, such as soft plastic foils, have a higher potential for entanglement in vegetation, and a lower potential for remobilization, compared to items with a low level of flexibility. The aim of this study is to identify riverbank characteristics that explain high plastic accumulation rates.

How to cite: Hauk, R., van Emmerik, T. H. M., van der Ploeg, M., Boonstra, M., de Winter, W., and Teuling, A. J.: Linking macroplastic deposition to riverbank characteristics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6634, https://doi.org/10.5194/egusphere-egu23-6634, 2023.

Plastic pollution is one of the major global water quality issues. Yet the lack of consistent data and standardized monitoring and assessment methods leads to a wide range of uncertainties in estimating the plastic load that is being delivered to marine environments. At the same time, continental and global dynamic hydrological models are becoming more available for large-scale 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).

Here, we present the first results from simulating global riverine plastic pollution using WWH. The model development is based on the results of the global literature review of sources of microplastics through the lens of a hydrological modeler. 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 applied in the collected monitoring studies, as well as large uncertainty and a lack of current knowledge of transport and transformation processes in water bodies. Thus, an ensemble of WWH model setups was developed where the model structure and hydrology is the same and the model parameters that affect generation, transformation, and transport of plastic from various land uses, sanitation categories, and in rivers are varied to explore the defined parameter space. 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. Further model error analyses indicate which sources and processes play an important role in transport of riverine plastics as well as how different monitoring approaches can affect the results.

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

How to cite: Bartosova, A., Jeppsson Stahl, F., Brendel, C., Temnerud, J., Havelka, J., and Arheimer, B.: What can global hydrological models tell us about sources and flows of riverine plastics?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13804, https://doi.org/10.5194/egusphere-egu23-13804, 2023.