This session welcomes contributions from field, laboratory and modelling studies that aim to advance our understanding of river network and catchment-scale plastic transport and accumulation processes. We are soliciting studies dedicated to all plastic sizes (macro, micro, nano) and across all geographic settings. We are especially encouraging studies that can link plastic accumulation and transport to catchment-wide hydrological, ecological or geomorphological processes that we can better understand where, when and why plastics accumulation takes place in aquatic-terrestrial environments.
In this session, we explore the current state of knowledge and activities on macro-, micro- and nanoplastics in freshwater systems, focusing on aspects such as:
• Transport processes of plastics at catchment scale;
• 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);
• Plastic in rivers, lakes, urban water systems, floodplains, estuaries, freshwater biota;
• Effects of hydrological extremes, e.g. accumulation of plastics during droughts, and short-term export during floods in the catchment;
• Modelling approaches for global river output estimations;
• Legislative/regulatory efforts, such as monitoring programs and measures against plastic pollution in freshwater systems.
Continuous human intervention in the environment has profoundly reshaped natural landforms, often disrupting their environmental functions to serve anthropogenic needs. The Krotenbach, located just south of Vienna (Austria), is a 14.2 km long, highly modified stream engineered to efficiently transport its water discharge. Further downstream from its production zone in the Wienerwald, the river partly flows through and beneath an urban–industrial area before continuing through agricultural land. These two distinctive sections are separated by one of the main highways in Austria, with the sampling area located downstream of this boundary. At the upstream limit of the study section, a wastewater treatment plant continuously contributes approximately 78% of the total river discharge, creating a persistently altered flow regime. This strongly anthropogenic system offers an ideal flume-like field laboratory to study the transport and accumulation of microplastics in riverbed sediments.
Despite its constricted planar morphology, low slope gradient, and limited sediment supply, the most significant depocenters were sampled for microplastic concentrations (>63 µm), sediment grain-size analysis, and total organic carbon content. In addition, all large wood elements and anthropogenic obstacles with sediment retention potential were mapped and quantified using field-based geomorphological indices of sediment connectivity, defined here as the efficiency of sediment transport from point A to point B within a defined system. A sediment connectivity model was therefore developed based on cumulative drainage area, channel slope, and retention indices for large wood and anthropogenic obstacles, to help predict and explain MP deposition patterns.
The primary objective of this research is to evaluate which fluvio-geomorphological sinks have the highest capacity to store microplastic particles (MPs) and to assess the extent to which their preferential occurrence can be explained by particle morphometrics, density, and their response to the relative degree of sub-watershed connectivity. Alongside sedimentary facies characterization, MP datasets were evaluated using a newly developed semi-quantitative sediment retention index to predict the sedimentological component of their riverine transport behaviour. Results show that the index developed for this study satisfactorily captures the physical principles likely governing microplastic transport. Comparisons between observed concentrations and model predictions highlight the sedimentary behaviour of microplastics deposited in riverbed sediments. Both MPs and mineral sediments appear to respond, through their respective fragmentation capacities, to hydraulic sorting under the same energy gradient.
Samples collected six months later, in October 2025, show a net decrease of over 50% in MP concentrations, particularly in sinks characterized by high bed shear stress. This second sampling campaign highlights the short residence time of MPs and the overall high connectivity of such a man-made river system. The role of small urban catchments in plastic pollution dynamics should therefore be prioritized in plastic pollution mitigation and remediation strategies.
All MP concentrations were corrected for contamination using six laboratory blanks and two field blanks. Recovery tests conducted with high-density 125 µm polyethylene yielded a recovery rate of 87.6%. Microplastics were identified through manual mapping using micro-FTIR analysis, with an analytical variability of 2.22% (standard deviation) based on 25% sub-sampling.
How to cite: Roudbar, S., Poeppl, R., Le Heron, D., and Wagreich, M.: Microplastic deposition and transport in a highly-modified stream: insights from geomorphic depocenters and sediment analogues, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5823, https://doi.org/10.5194/egusphere-egu26-5823, 2026.
This study examined the distribution and interaction of microplastics (MPs) between water and sediment matrices across lake and river systems in Krishnagiri District, Tamil Nadu, India, emphasizing the influence of hydrodynamic conditions on their transport and deposition. A total of 3,050 MP particles were detected, with water samples contributing 47.47% (1,185 particles from 21,115 L) and sediments 52.53% (1,865 particles/kg). Fibers dominated water samples (92.4%), whereas sediments exhibited greater MP diversity, including fragments, fiber bundles, beads, films, and foams (26.5%), indicating enhanced accumulation and heterogeneity due to long-term deposition. A strong negative correlation was found between water velocity and MP concentration in water (ρ = –0.82, p = 0.001), suggesting that higher velocities reduce MP retention. No significant correlation was observed between water velocity and sediment MPs (ρ = 0.18, p = 0.5), implying that topography and depositional conditions exert stronger control on MP accumulation. Spatial analysis of water-to-sediment MP concentration ratios revealed that eight of eleven river sites exhibited higher MP loads in sediments, particularly in wider and low-velocity zones, where reduced turbulence promotes MP settling. Confluence points showed elevated MP concentrations in water due to enhanced hydrodynamic mixing, sediment disruption, and resuspension of buried particles. Lakes also exhibited higher MP concentrations per litre than rivers, reflecting their role as long-term sinks. Overall, results demonstrate that hydrodynamics, geomorphology critically govern MP transport, retention, and distribution within freshwater ecosystems, providing insight into their environmental fate and informing mitigation strategies for aquatic plastic pollution.
How to cite: Mohan, K. and Lakshmanan, V. R.: Microplastics in freshwater environments: Influence of topography and water velocity on their distribution in river systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12271, https://doi.org/10.5194/egusphere-egu26-12271, 2026.
Microplastics (MP) are constantly transported into the oceans via rivers, but riverine transport paths linking MP sources and sinks are insufficiently understood. For a quantification of MP transport in rivers, knowledge on the differential behaviour of MP and natural sediments in aquatic environments is essential. Both underlie the same hydrodynamic forces, namely gravity, buoyancy and drag force but MP exhibits strong contrast to natural sediments in terms of particle density and form enhancing the complexity of MP transport compared to natural sediments. Therefore, the main objective of our research is to gather knowledge on the application and comparison of different sampling techniques to obtain information on the temporal variability of MP in the Rhine River in Germany and identify monitoring techniques to efficiently calculate MP-loads in river systems.
Here we present various monitoring devices to estimate mass-based MP concentrations in the Rhine, and test different algorithms to calculate MP loads, considering the spatio-temporal variability of MP occurrence in rivers. MP concentrations are monitored for one year at Weil am Rhein (at the Swiss-German border), Koblenz and Emmerich (at the German-Dutch border). For the analysis of the collected samples, thermal degradation techniques (Pyr-GC-MS) are applied to obtain mass-based concentrations for polypropylene (PP), polyethylene (PE), polystyrene (PET) and polyvinyl chloride (PVC) for four grain size fractions ranging from 10 to 1000µm.
Total annual MP loads at Koblenz in 2022/23 are 429±125 t derived from the SB and 58±15 t derived from the CFC. Much lower loads derived from the CFC indicate that flow centrifuges might capture large amounts of heavy polymers with densities > 1 g cm-3, but retain only a small fraction of MP particles < 1 g cm-3. CFC sampling is frequently applied for water quality analysis and known for its high sampling efficiency regarding mineral particles. However, monitoring MP using CFCs requires additionally sampling and analysing of the residual water of the CFC, to avoid the loss of low-density polymers.
The comparison of the monitoring using SBs at the three sampling sites reveal significant longitudinal gradients of MP transport along the Rhine. The MP load of PP, PE and PET in 2022/23 increases from 230 t a-1 at the Swiss/German border to 357 t a-1 at Koblenz and 460 t a-1 at Emmerich, with dominating PE loads followed by PP and PS.
The estimated MP loads are among the highest of the world. Based on a rating analysis MP-load with catchment size, we are able to show that these high loads are linked to the large catchment sizes of the River Rhine compared to othr MP-load estimates.
How to cite: Hoffmann, T., Range, D., Kamp, D., and Ternes, T.: Monitoring microplastic transport in the Rhine River, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21946, https://doi.org/10.5194/egusphere-egu26-21946, 2026.
Rivers play a central role in the global distribution of plastic pollution, as plastics are both retained and exported to sea. Large scale plastic transport models are used to quantify plastic export. Despite recent research showing that the majority of plastic is not transported to sea, most models have overlooked reporting a key process in plastic transport dynamics, quantifying the retention of plastic in rivers. Moreover, previous models have carried out limited model calibrations, leading to uncertainty in export estimates. These gaps in knowledge have resulted in models potentially over or underestimating plastic export, and providing a limited assessment of the overall plastic pollution of a river system. We propose a new model to explore the state of plastic pollution accounting for both micro- and macroplastic considering both river export and retention on land and in rivers at a European scale. We find that rivers are a significant temporary sink for plastics with a large quantity of plastic being retained in Europe rivers systems on an annual scale. River basins with a large area and input of plastic to land contribute considerably to absolute plastic export and retention. When accounting for population density, we find that small coastal river basins are estimated as having a larger macroplastic export per capita compared to larger basins. Conversely large river basins are estimated as having the largest microplastic export per capita. This outcome shows the complexity of plastic export and retention and reinforces the need to model at a high spatial resolution for accurately characterizing pollution dynamics. We determine that reducing plastic generation and mismanaged inputs to land is fundamental to achieving meaningful reductions in plastic pollution. Finally, we show that using a single indicator (e.g. plastic export or retention in rivers) to determine the most polluted rivers may not be sufficient in determining the overall level of plastic pollution of a river system. By integrating estimates of plastic retention, the final assessment of plastic pollution reveals a different set of high polluting rivers, than if only export estimates were to be used. By carrying out this research we provide a holistic overview of the overall state of pollution in Europe’s rivers by evaluating plastic export and retention estimates using a well calibrated, high resolution model.
How to cite: Stibora, M., van Emmerik, T. H. M., Waldschläger, K., Sánchez-Guerrero Hernández, M. J., Everaert, G., and Weerts, A.: Plastic retention and export across Europe's rivers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19183, https://doi.org/10.5194/egusphere-egu26-19183, 2026.
Plastic pollution threatens the health of humans and aquatic and terrestrial ecosystems worldwide. Addressing this threat with effective strategies and solutions requires a clear understanding of the processes that control the fate and transport of mismanaged plastics at various scales, from watersheds to regions and even continents. River corridors serve as dominant pathways and traps for mismanaged plastic generated within the landscape, which eventually reaches the ocean. In this work, we examine the main sources of plastic pollution globally and share findings from a new flow and transport model for plastic waste in riverine environments. Our results show that only about 0.25% of the mismanaged plastic entering rivers since the 1950s is expected to reach the ocean by 2100, with most plastic being stored in freshwater ecosystems. Patterns of plastic buildup and how long it stays depend heavily on (i) topology and geometry of the river network and (ii) the position and trapping efficiency of flow regulation structures, especially large dams. Our model highlights the crucial role of rivers as significant sinks for plastic waste and emphasizes the importance of targeted remediation strategies that consider river network structure and human-made controls when designing interventions and sampling plans. These measures can help maximize benefits and set realistic expectations.
How to cite: Gomez-Velez, J. and Krause, S.: Tracing Plastic Pathways: A Global Perspective on Its Fate and Transport Along River Corridors, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14039, https://doi.org/10.5194/egusphere-egu26-14039, 2026.
Several estimations of global plastic emissions exist; however, the photodegradation of plastic litter and the complex hydrological processes on land have not been adequately integrated into these models. This study simulates the generation and emission of nano- and microplastic (NMP) particles using the Catchment-based Macro-scale Floodplain (CaMa-Flood) model to elucidate their hydrodynamics.
First, a photodegradation model for plastic litter was established through accelerated ultraviolet (UV) weathering tests under dry and wet conditions. The mass of plastic litter decreased linearly with the cumulative UV irradiation dose, with wet conditions exhibiting a lower mass decay rate than dry conditions. By incorporating these linear relationships and the ratio of rainy days, we estimated the NMP generation rate across Japan. Subsequently, NMP emissions were diagnosed using a new scheme implemented within the CaMa-Flood model and validated against microplastic observation data from 177 sites. The simulated concentrations showed strong consistency with observed data.
Notably, our simulation focuses on the seasonal variations in the amount of plastic retained on land. We identified a distinct "first flush" effect during the rising stages of floods and observed how spatial distributions of surface runoff influence NMP transport. These results demonstrate that the CaMa-Flood model is a robust tool for understanding the terrestrial hydrodynamics of NMP particles and estimating plastic fluxes. This framework provides a basis for future global-scale estimations to identify NMP accumulation hotspots driven by hydrodynamic processes.
How to cite: Kataoka, T., Oe, H., Furutani, M., Nihei, Y., and Yamazaki, D.: Hydrodynamics of terrestrial nano- and microplastics: simulating seasonal retention and first-flush emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8615, https://doi.org/10.5194/egusphere-egu26-8615, 2026.
Estimates suggest millions of metric tonnes of plastic enter aquatic ecosystems annually, with urban environments acting as a primary source of this leakage. Within cities, waterways such as rivers, streams, and canals act as arteries to collect and transport land-based plastic waste outside the city boundaries. While the source of cities for aquatic plastic pollution is clear, the understanding of processes governing the journey of plastic through cities and the drivers of transport and accumulation within cities is limited. Here, we characterize the baseline patterns of floating plastic by mapping the spatial distribution and temporal variability of plastic accumulation and transport across Amsterdam, by using a database of nearly 10,000 monitored plastic items with monthly monitoring sessions between November 2022 and October 2023. Plastic accumulation and transport are neither uniform in space nor constant in time. We further identify and explore the explanatory power of site-specific urban features that may drive plastic abundance at the local level. We reduced 87 urban environmental features to 8 principal components, which describe unique gradients in the urban landscape. By correlating these principal components with our plastic observations, we identify that spatial patterns differ substantially between the accumulation of plastics and the transport of plastics. Some plastic types are widely distributed across multiple urban gradients, where others are strongly associated with specific urban contexts. Most plastic types show no significant correlations, highlighting the complex nature and ubiquity of plastic in all urban contexts. We highlight that item-specific data is necessary to disentangle the complex nature of urban plastic pollution. By analyzing which items tend to co-exist, potential clustering of items, and their abundance in the context of specific urban features, we are getting closer to detecting the true sources and drivers of urban plastic pollution.
How to cite: Tasseron, P., van Emmerik, T., Qiu, Y., and van der Ploeg, M.: It's complicated: the relationship between urban features and aquatic plastic pollution, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5390, https://doi.org/10.5194/egusphere-egu26-5390, 2026.
Resolving the vertical velocities and three-dimensional dynamics of macroplastics and other anthropogenic litter is critical for developing comprehensive hydrodynamic models of litter transport in rivers – both vertically in the water column and horizontally across the channel. Employing large settling tanks, with a synchronous multi-camera system and an automated plastic detection algorithm, we reconstruct in three-dimensions the settling and rising trajectories more than 1,000 litter items. This enables characterisation of a litter item’s vertical and horizontal velocities, as well as their drifting gradient, oscillatory motions and settling patterns. Settling and rising velocity distributions are presented for 24 River-OSPAR categories, which represent approximately 80% of the most persistent litter categories found in rivers and on riverbanks, and include items such as plastic bags, food wrappers, and cigarette filters. The velocity distributions for each River-OSPAR category support realistic inputs for hydrological models of litter transport. Individual trajectories are then classified into four regimes – linear, linear drifting, nonlinear and nonlinear drifting – based on lateral displacement and zero-crossing analysis. This classification allows construction of a regime map of settling and rising dynamics as a function of a litter’s geometry and density, delineating regions in which different River-OSPAR categories exhibit distinct settling behaviours. The resulting regime map and velocity statistics provide physically based inputs for hydrodynamic models aimed at predicting the mobilisation, transport, and fate of litter in riverine environments.
How to cite: Lofty, J., Valero, D., and Franca, M.: Database for the setting and rising dynamics of river litter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17376, https://doi.org/10.5194/egusphere-egu26-17376, 2026.
Rivers play an important role in the global distribution of plastic pollution. Plastics are transported and retained by rivers, and may be exported to sea. Large-scale, long-term and harmonized plastic monitoring data are crucial to better quantify, understand, and reduce plastic pollution in the environment. Global data availability strongly depends on the river compartment (surface, water column, riverbank, sediment) and size range (micro or macro). Despite the surge in data collection efforts, a comprehensive framework to combine those data into actionable plastic pollution indicators is still lacking. Here, we present a methodology to holistically assess the state of plastic pollution for river systems. We defined eight plastic pollution indicators representing different river compartment and size ranges. All indicators can be quantified using commonly used monitoring methods. Indicator values are coupled to effect thresholds of microplastic and macroplastic, and combined to quantify the overall state of plastic pollution. Our method can be applied at multiple spatiotemporal scales. We applied our assessment method to the Netherlands, and included four rivers, two estuaries and five urban water systems. We show that the state of plastic pollution at the annual scale varies strongly between systems, changes over time, and is driven by different indicators (e.g. suspended macroplastic, floating macroplastic or riverbank macroplastic). With our work we aim to contribute to the development of comprehensive, globally applicable tools to assess plastic pollution in rivers.
How to cite: van Emmerik, T. H. M., Liese, N., Schreyers, L. J., Stibora, M., Tasseron, P. F., Pinto, R., Schmidt, C., Everaert, G., Rochman, C., and Koelmans, A. A.: Assessing the state of plastic pollution in Dutch river systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13961, https://doi.org/10.5194/egusphere-egu26-13961, 2026.
Studies on microplastic (MPs) pollution in aquatic environments have been conducted for over 20 years, developing and implementing a wide array of sampling and analytical methods to capture their complexity and variability in waters. However, the selection of different sampling equipment, minimum particle size considered, and sample size (sampling volume), have led to a series of potential methodological biases. This could hinder comparison of results and, therefore, understanding actual environmental variability among studies and geographical regions. In the case of different minimum particle size and size range reported, which directly impact the particle counts in the sample (e.g., smaller particles are numerous), correction factors were developed to align the concentrations found to a predefine microplastic size range (Koelmans et al., 2020; Xue et al., 2024). However, other factors, such as the potential bias caused by sampling volume on concentration is not well understood.
In this work, we developed a statistical model to isolate the effect of sample size in freshwater samples. Literature mining allowed the study of 7506 samples, from 363 studies, collected by the most common sampling equipment: Nets, pumps and bottles (grab sampling). Each of these methods showed a wide range of mesh/filter sizes used and sampling volumes. We first corrected concentrations to a default size range (0.02 mm – 5 mm) using the correction factor by Koelmans et al. (2020) to remove bias caused by size. Second, we identified that the sampling volume and the size-corrected concentration remained negatively correlated (rho = -0.7, p-value < 0.01), indicating an additional methodological bias. Third, we modelled this correlation through a regression analysis, adjusting the parameters to allow a secondary correction due to sampling volume. The residual term of the regression model was interpreted as the actual environmental variability (i.e., spatiotemporal variation in concentration) to preserve the actual differences between sampled sites. Finally, a ‘normalized concentration to a standard volume’ was obtained, minimising both methodological biases.
This normalized concentration allows assessing microplastic contamination level in each sample, irrespective of the method used. The mapping of the corrected concentrations reveals a new regional distribution in the intensity (by orders of magnitude) of the microplastic contamination in global rivers, where those areas oversampled using higher sampling volumes show higher levels of pollution than previously thought and vice versa.
References
Koelmans, A. A., et al. (2020). Solving the nonalignment of methods and approaches used in microplastic research to consistently characterize risk. Environmental science & technology, 54(19), 12307-12315.
Xue, Y., et al. (2024). Standardization of monitoring data reassesses spatial distribution of aquatic microplastics concentrations worldwide. Water Research, 254, 121356.
How to cite: Sánchez-Guerrero Hernández, M. J., Quintana, R., Manzano-Medina, S., and van Emmerik, T.: Identification of methodological biases to assess global levels of microplastic pollution in rivers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11995, https://doi.org/10.5194/egusphere-egu26-11995, 2026.
Plastic transport processes in inland fluvial systems remain poorly quantified, particularly at larger spatial and temporal scales. In this study, we aim to investigate macroplastic transport dynamics across multiple river reaches, even river system using a combination of field observations, remote sensing, and modelling approaches, with relevance at catchment scale.
We are developing an integrated monitoring system capable of continuously surveying extended river sections using multiple fixed monitoring stations equipped with IP cameras and automated object detection algorithms. In addition, unmanned aerial vehicles (UAVs) are employed for rapid assessments of highly polluted areas and spatially heterogeneous accumulation zones. The primary output of this system is a continuous time series of macroplastic fluxes across multiple river cross-sections, enabling direct coupling with hydrological, meteorological, and catchment-scale land use data.
To further investigate macroplastic transport pathways, accumulation zones, and remobilization processes, we are also developing and testing GPS-equipped plastic tracers that can be tracked over extended periods with meter-scale positional accuracy. These observations allow the identification of trapping zones, residence times, and remobilization probabilities under varying hydrological conditions, including the influence of extreme events such as floods and low-flow periods.
The collected spatio-temporal datasets address current gaps in long-term, reach-to-catchment scale observations of macroplastic transport in freshwater systems. These data are intended to support and calibrate hydrodynamically driven, particle-based (Lagrangian) transport models, improving our understanding of macroplastic source-to-sink dynamics and the role of hydrological and land use controls on plastic accumulation and export in riverine environments.
How to cite: Tikász, G., Fleit, G., and Turák, B.: Monitoring and modelling macroplastic transport in riverine systems from reach to catchment scale, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21645, https://doi.org/10.5194/egusphere-egu26-21645, 2026.
In natural environments, the biodegradation of synthetic polymers depends on microorganisms that colonize polymer surfaces and secrete extracellular enzymes capable of depolymerizing these materials into low-molecular-weight compounds, which can subsequently be taken up and metabolized by the cells. To date, several microorganisms capable of hydrolyzing insoluble polymers have been identified. In contrast, limited information is available about aquatic microorganisms and the extracellular enzymes that mediate the biodegradation and mineralization of water-soluble polymers (WSPs). Water-soluble polymers are increasingly used in a wide range of applications such in cosmetics and home care products, and their incorporation into liquid formulations facilitates their entry into technical systems such as wastewater streams and wastewater treatment plants (WWTPs), as well as into natural aquatic environments.
In this study, we identified microorganisms and their enzymes that are capable of hydrolyzing WSPs. Hydrolases from various Pseudomonas species were identified and produced that hydrolyze structurally different ionic phthalic acid-based polyesters. In addition, the aerobic biodegradation of the polyesters in simulated fresh water with sewage sludge as inoculum was investigated. Beyond phthalic acid–based polyesters, synthetic poly(amino acids) represent another industrially relevant class of water-soluble polymers for which enzymatic biodegradation is still poorly understood. The most commercially successful synthetic poly(amino acid) is the water-soluble, anionic polymer poly(aspartic acid) (tPAA). Despite its widespread use, little is known about the biodegradability of tPAA. In this study, we investigated the interactions between tPAA and hydrolases derived from Sphingomonas sp. KT-1 and Pedobacter sp. KP-2, and assessed the effects of these enzymes on tPAA biodegradation. Detailed analyses using recombinant enzymes were conducted to characterize their activities and to elucidate potential synergistic effects during tPAA degradation. Finally, the individual and combined effects of the hydrolases were evaluated using an OECD 301F biodegradation test, demonstrating the potential of integrating specific enzymes into existing standardized tests to shorten testing times and to gain deeper insights into polymer biodegradation processes.
How to cite: Ribitsch, D., Binder, K., and Gübitz, G.: When Plastics Meet Microbes: Biodegradation in Aquatic Environments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11735, https://doi.org/10.5194/egusphere-egu26-11735, 2026.
In order to better understand the processes of transport and accumulation of microplastics with other co-pollutants, we developed a large-scale study along the UK's longest river, the River Severn (354 km). Our objective is to quantify the concentrations and loads of MPs and metal elements in sediments and surface water, and also to discuss their origin by considering tributary inputs and land-use changes. River Severn successively flows through a diversified landscape with forested uplands and pasturelands, where former mining areas (lead, silver and zinc) are found (Shropshire and Plymlimon). It also presents small towns which originally developed thanks to wool production and heavy industries. Downstream, the river receives inputs from tributaries draining urban and industrial areas (Birmingham Black Country and Coventry), as well as wastewater treatment plant inputs (around Worcester).
Streambed sediments and surface water from 16 sites located along the river were collected during low water conditions to take into account this spatial feature. MP concentrations and polymer types were quantified by using µFT-IR. Metal concentrations (Cd, Cu, Cr, Fe, Ni, Pb, Zn) as well as hydrological and sediment properties (grain size, organic matter – OM, carbonates) were also acquired during the sampling campaign. Pollution Load (PLI) and Polymer Risk (PRI) indices, as well as daily MP fluxes were assessed.
Results highlight multi- contaminated hotspots in the upstream section (PLI>2), mostly because of lead (Pb), zinc (Zn) and cadmium (Cd) due to diffuse pollution from historic mining areas, while MP hotspots were distinct and limited. A gradual growth of metals and MP concentrations and loads as well as an increase of polymer diversity occurred in the downstream direction, in both surface water and sediments. A major multi-pollution hotspot was found south of Worcester (PLI>5), which seems polluted by both diffuse pollution from tributaries (such as the Avon River coming from Coventry) and by local sewage inputs.
The composition of pollution hotspots greatly contrasts along the river, as underlined by various metal and MP concentration and types, most likely coming from point-sources, as well as brought by some tributaries draining urban-industrial areas in the downstream direction. This knowledge gain will help to shape future river water quality management.
How to cite: Dendievel, A.-M., Mourier, B., Haverson, L., Iannuzzi, Z., Kelleher, L., Kukkola, A., Schneidewind, U., and Krause, S.: Spatial Variability and Combined Risk of Metal elements and Microplastics along the River Severn (UK), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3830, https://doi.org/10.5194/egusphere-egu26-3830, 2026.
Riverine plastic pollution is commonly quantified using point-based flux measurements, yet the transport pathways and residence times of floating litter between monitoring locations remain poorly understood. This limits both the interpretation of flux data and the effective placement of interception and cleanup strategies. In this study, we investigate whether GPS tracers can be used to characterize the movement patterns of floating plastic in (semi)urban waterways.
Multiple field experiments (±60 sensors) were conducted across Dutch waterways (Alkmaar, Zaandam, Leeuwarden) in different seasons, during which floating GPS trackers were released and tracked over periods ranging from several days to eight weeks. The resulting trajectories were analysed in terms of cumulative distance travelled, lateral distribution within the channel, and temporal movement patterns.
Across all release locations (six in total), transport was found to be highly intermittent: long periods of little to no movement were frequently interrupted by short bursts of rapid displacement, resulting in stepwise cumulative distance curves. Spatially, trajectories showed a strong preference for near-shore transport rather than mid-channel flow. Floating proxies were repeatedly observed to accumulate along banks, where movement was often halted by obstructions such as vegetation, moored vessels, and infrastructure. These stagnation periods strongly influenced overall travel distance and residence time.
The results demonstrate that floating plastic transport in urban water systems cannot be approximated as continuous downstream movement. Instead, it is governed by intermittent mobilisation and frequent temporary retention along channel margins. GPS-based measurements therefore provide critical complementary information to flux monitoring, helping to explain variability in observed litter counts and supporting more effective design and placement of monitoring and interception systems. This approach offers a scalable pathway to bridge the gap between local flux measurements and system-wide transport dynamics of urban plastic pollution.
How to cite: van Wijk, J.: Floating GPS tracker measurements reveal intermittent and shoreline-driven transport of floating plastic in urban waterways, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3290, https://doi.org/10.5194/egusphere-egu26-3290, 2026.
Rivers are major pathways for plastic pollution to oceans, with high emissions observed in tropical regions. Invasive water hyacinths (WHs) can trap macroplastics and serve as proxies for detecting river plastic using remote sensing. We explore how this phenomenon and its detection methods are transferable to Thailand’s Chao Phraya River. Along a 62 km river course, up to 78% of floating plastics were trapped in WHs (average 32%), comparable to the Saigon River (58–82%). Although trapped proportions decreased downstream, plastic concentration in WHs was 59 times higher than in open water. Object detection models transferred well for WHs and entangled plastics (Chao Phraya: mAP50 = 68% and 54%; Saigon River: mAP50 = 70% and 52%), but poorly for free-floating plastics (23% vs. 48%). Physical sampling found 14 times more plastics within WHs than imagery, highlighting WHs’ role in trapping plastics and their potential role in monitoring and clean-up efforts.
How to cite: Hagenbeek, G., van Emmerik, T., Jia, T., Khamdahsag, P., Boonma, K., Taormina, R., Mani, T., and Rußwurm, M.: Exploring Transferability of Plastic-Water Hyacinth Interaction and Detection in Rivers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3434, https://doi.org/10.5194/egusphere-egu26-3434, 2026.
Is the distribution of macroplastic along rivers stable over time? Rivers transport and accumulate macroplastic litter, and large amounts of macroplastic are deposited on riverbanks. It seems there are factors and variables linked to macroplastic deposition at a specific location, e.g. riparian vegetation or population density. However, the specific transport and deposition processes that lead to a plastic item being deposited on a specific riverbank are not well understood yet. So we took a step back and instead of analyzing local riverbank characteristics that might link to plastic deposition, we investigated the stability of plastic deposition over time. If macroplastic distribution is indeed stable over time, it further indicates that there is a link between macroplastic deposition and site specific factors.
We adapted a method, which was originally developed to analyse the temporal stability of soil moisture. With that method, we assessed the temporal stability of macroplastic distribution on 229 riverbanks along eight major Dutch rivers. Each location was surveyed between six and eight times from 2020 to 2024. Our results demonstrate clear temporal stability in macroplastic distribution over those four years. Riverbanks were classified into four categories, hotspots, coldspots, and persistently above- or below-average sites, based on their relative plastic concentration over time. Between 10% and 42% of sites along each river were identified as coldspots with a plastic concentration always below average. At the other end, 0% to 8% were persistent hotspots, with a plastic concentration always above average. We also identified that the hotspots contained a disproportionally large amount of macroplastic, between 13% to 35% of macroplastic items for the rivers that had hotspots.
The proposed method offers a practical and relatively easy approach to investigate the temporal stability of macroplastic distribution between locations. Assessing this temporal stability (or lack thereof) can provide a new perspective on macroplastic pollution in the investigated system. It can also contribute to optimize macroplastic monitoring and focus mitigation measures. Further, the demonstrated spatial and temporal stability implies underlying mechanisms governing macroplastic deposition. This provides a direction for future process-based investigations.
How to cite: Hauk, R., van der Ploeg, M. J., van Emmerik, T. H. M., and Teuling, A. J.: Temporal stability of macroplastic on Dutch riverbanks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6575, https://doi.org/10.5194/egusphere-egu26-6575, 2026.
Rivers represent major pathways for microplastic (MP) transport from land to the oceans. MP transport and deposition processes in rivers are influenced by complex hydraulic flow behavior of the river and its interactions with streambed, vegetation and infrastructure as well as the physicochemical properties of MPs themselves. While there is increasing understanding of the hydrodynamic controls on the transport behavior of MPs of different density, size and shape, the impact of geochemical interaction of MPs with other compounds, including possible co-precipitation with minerals remains poorly understood. We here reveal the potential for enhanced MP deposition from the rivers in karst regions through co-precipitation with carbonate minerals through a large-scale field observation covering the entire Pearl River Basin. This is supported by the substantially greater difference in MP mean density between the river water and sediments in carbonate-dominated basins compared to non-carbonate-dominated basins. Laboratory experiments demonstrate that co-precipitation of CaCO₃ and MPs can occur in rivers of carbonate-dominated basins, which enhances MP deposition on the streambed. The negative surface charge of MPs adsorbs Ca2+ and increases the possibility of CaCO₃ precipitation on the surface of MPs. MPs of smaller size and higher electronegativity, such as polyamide (PA), show greater affinity for Ca2+ and higher deposition ratio from the water column via co-precipitation with CaCO₃. At global scale, regions with high proportion of carbonate bedrocks are characterized by reduced riverine MP exports to the ocean as more of them deposited at the streambed. Our findings underscore the critical role of carbonate mineral precipitation depending on the geological background in regulating fluvial MP deposition and retardation in rivers. This newly described mechanism provides a theoretical basis for future MP mitigation strategies in rivers with different bedrock geology.
How to cite: Wang, H., Mai, L., Krause, S., and Liu, Y.: Carbonate mineral precipitation enhances microplastic deposition in karst rivers globally, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7802, https://doi.org/10.5194/egusphere-egu26-7802, 2026.
Key words : Caribbean, GPS, Macroplastics, Monitoring, Rivers, Tracking
Urban tropical rivers serve as critical pathways for macroplastic transport from land to sea, yet their true ocean-emission potential remains poorly understood. This study represents the first application of satellite-enabled GPS tracking in an insular Caribbean river system to quantify the movement of floating macroplastics. A total of 68 GPS drifters were deployed across the Ozama-Isabela river system in Santo Domingo, Dominican Republic, during three distinct seasonal phases in 2022. Devices were released from main river channels and tributary ravines (cañadas), and their trajectories were recorded over periods of up to three months. Results showed that 54% of drifters reached the Caribbean Sea, with river-released devices exhibiting higher transport efficiency (mean speed: 3.47 km/day) compared to those from cañadas (mean speed: 1.38 km/day). Transport dynamics varied significantly by season, with increased connectivity during high-precipitation periods. Instead of a linear predictive model, statistical analysis of the trajectories revealed a bimodal flow regime governed by a high-velocity central "transport hotline." Gaussian Mixture Models distinguished two physical states: rapid advection in the channel thalweg and static retention at the river margins. Furthermore, a significant lateral asymmetry was identified, with the right bank acting as a preferential retention zone (58% of marginal interactions). These findings demonstrate that plastic export is a binary mechanism determined by the debris' capacity to enter and remain within the central hotline. This study offers new empirical insights for regional management, suggesting that mitigation strategies must prioritize interception in tributaries before waste enters the rapid-transit main channel where capture becomes increasingly difficult.
How to cite: Garcia Estevez, R., Gonzalez, W., Sanlley, C., Mani, T., and Mozrall, A. M.: Transfer of Macroplastic Debris from Low-Tide Tropical Urban Estuaries to the Caribbean Sea: A Case Study from the Ozama-Isabela River , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8681, https://doi.org/10.5194/egusphere-egu26-8681, 2026.
Key words: Debris flux, Urban Rivers, Plastic Pollution, Long – term monitoring, Caribbean Sea
Plastic pollution is a globally widespread threat to aquatic habitats. Models estimate that rivers carry up to 2.7 million tonnes of plastic waste into the world’s ocean every year, with the highest emission rates associated with seasons of high rainfall and discharge. The Caribbean is markedly impacted by this problem due to poor waste management and high coastline-to-landmass ratio of its multi-insular landscape. Model numbers are stated under multiple orders of magnitude of uncertainty, due to a lack of long-term, continuous empirical monitoring data. Draining the 3.5 million-inhabitant Dominican capital city of Santo Domingo, the Rio Ozama is estimated to emit between 220–22,000 tonnes (midpoint: 2,200) of plastics per year – one of the largest contributors of plastic pollution to the Caribbean Sea. This study seeks to reduce the uncertainty gap through long-term empirical baseline data. For this, we equipped two bridges across the final kilometers of the Rio Ozama with each four water-facing cameras. The sensors collected hourly debris flux data during daylight for one year (2022–2023). The resulting data indicate a median annual anthropogenic debris flux of approximately 630 tonnes year⁻¹, with an uncertainty range between ~294 and ~1,291 tonnes year⁻¹ (25th–75th percentiles), placing the observed emissions within the lower-to-mid range of previously modelled estimates for the Rio Ozama. The upstream Rosario Bridge recorded a median debris load of ~191 tonnes year⁻¹, while the downstream Mella Bridge registered ~439 tonnes year⁻¹. Expressed as Rosario/Mella, the ratio was ~0.43, indicating that debris loads at the Rosario Bridge were approximately 57% lower than those observed at the Mella Bridge over the ~3.3 km monitored river reach. This downstream increase reflects the substantial contribution of urban ravines (cañadas) and localized waste inputs entering the river between both monitoring points. Seasonal variability in debris flux was lower than expected, suggesting that anthropogenic sources and retention–release mechanisms exert a stronger control on debris transport than hydrological mobilization alone. The continuous, high-frequency dataset provides a robust empirical baseline for calibrating riverine plastic emission models and for assessing the effectiveness of waste management policies and cleanup interventions.
How to cite: Gonzalez, W., Garcia, R., Sanlley, C., Mani, T., Pinson, S., and Mozrall, A. M.: Ozama River Case Study: One-Year Multiple-Camera River Monitoring to Establish Baseline Debris Flux from the Dominican Capital into the Caribbean Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8764, https://doi.org/10.5194/egusphere-egu26-8764, 2026.
Plastic pollution in surface waters spans a wide range of particle sizes, yet the transport dynamics of both micro‑ and macro‑plastics remain insufficiently quantified at the catchment scale. Addressing this challenge requires modelling approaches capable of linking realistic hydrological variability with particle‑specific transport behaviour. In this work, we develop a numerical framework that couples large‑scale hydrological simulations with a process‑based transport model for plastics of different size classes.
We begin by reusing and re‑calibrating the mesoscale Hydrological Model (mHM) using benchmark datasets and hypothetical test cases to generate space–time fields representing flow dynamics across river basins. These hydrological outputs are exported as NetCDF files, providing a consistent and high‑resolution description of discharge and flow conditions in surface waters. To simulate plastic transport, we extend the DRUtES modelling platform by implementing a module that reads the mHM‑generated NetCDF files and solves an ADER‑based advection–dispersion–reaction equation designed to represent the transport dynamics of both micro‑ and macro‑plastic particles under realistic hydrological forcing. This coupled framework enables the simulation of plastic transport across size classes and supports scalable assessments of plastic transport dynamics in river systems.
How to cite: Barati Moghaddam, M. and Kuráž, M.: Numerical modelling framework for micro and macro plastic transport dynamics in surface waters , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10063, https://doi.org/10.5194/egusphere-egu26-10063, 2026.
Riverbed sediments are critical transition zones that govern the exchange of water and contaminants, including microplastic particles (MPs), between surface water and groundwater. To improve our understanding of the fate and retention of MPs in these water-saturated, porous systems, we used a freeze-coring technique to obtain undisturbed, water-saturated sediment cores (100 cm in length), even in non-cohesive gravel sediments in two regulated federal waterways. We analyzed the abundance, polymer type, and size of MPs (≥ 100 µm) at 10-cm depth intervals and interpreted the observed vertical MP patterns using microplastics as novel artificial process tracers for sediment dynamics.
In the sandy riverbed of the Main River, we found a mean concentration of 21.7 MP/kg with a depth distribution that remained relatively constant in the upper layers (0–30 cm), decreased in the middle layers (30–60 cm), and markedly increased in deeper layers (60–100 cm). These vertical trends suggest a complex interplay of multiple sedimentary processes and the superimposition of factors controlling riverbed dynamics. In contrast, the gravelly riverbed of the Alpine Rhine showed a low mean concentration of 3.1 MP/kg, despite comparatively high MP concentrations in river water and groundwater, suggesting high MP mobility and limited retention of even large MPs (up to 929 µm) within the coarse sediments.
At both sites, the proportion of small MPs increased with depth; however, the largest MPs were detected in the deepest layers. While this pattern may be explained by particle infiltration processes in the Alpine Rhine, such a mechanism is implausible in the Main River, given its sandy sediment characteristics. Furthermore, low-density buoyant polymers and polymer types with the youngest EPO ages (e.g., PS ≈ 1953, PP ≈ 1954, and PET ≈ 1973) were found in deep, sandy sediments (> 80 cm).
Based on these characteristic vertical MP patterns, we propose using microplastics as a process tracer to infer controlling sediment processes, enhance the geohydraulic characterization of federal waterways, and support the long-term monitoring of sediment relocation in fluvial systems.
How to cite: Pittroff, M., Loui, C., Oswald, S. E., Lensing, H.-J., and Munz, M.: Microplastics as a potential process tracer for riverbed dynamics in federal waterways, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14734, https://doi.org/10.5194/egusphere-egu26-14734, 2026.
