Plastic pollution in the natural environment poses a growing threat to ecosystems and human healt... more Plastic pollution in the natural environment poses a growing threat to ecosystems and human health, prompting urgent needs for monitoring, prevention and clean-up measures, and new policies. To effectively prioritize resource allocation and mitigation strategies, it is key to identify and define plastic hotspots. UNEP's draft global agreement on plastic pollution mandates prioritizing hotspots, suggesting a potential need for a defined term. Yet, the delineation of hotspots varies considerably across plastic pollution studies, and a definition is often lacking or inconsistent without a clear purpose and boundaries of the term. In this paper, we applied four common hotspot definitions to plastic pollution datasets ranging from urban areas to a global scale. Our findings reveal that these hotspot definitions encompass between 0.8% to 93.3% of the total plastic pollution, covering <0.1% to 50.3% of the total locations. Given this wide range of results and the possibility of temporal inconsistency in hotspots, we emphasize the need for fit-for-purpose criteria and a unified approach to defining plastic hotspots. Therefore, we designed a step-wise framework to define hotspots by determining the purpose, units, spatial scale, temporal scale, and threshold values. Incorporating these steps in research and policymaking yields a harmonized definition of hotspots, facilitating the development of effective plastic pollution prevention and reduction measures.
Plastic pollution in the world’s rivers and ocean is increasingly threatening ecosystem health an... more Plastic pollution in the world’s rivers and ocean is increasingly threatening ecosystem health and human livelihood. In contrast to what is commonly assumed, most mismanaged plastic waste that enters the environment is not exported into the ocean. Rivers are therefore not only conduits but also reservoirs of plastic pollution. Plastic mobilization, transport and retention dynamics are influenced by hydrological processes and river catchment features (for example, land use, vegetation and river morphology). Increased river discharge has been associated with elevated plastic transport rates, although the exact relation between the two can vary over time and space. However, the precise role of an extreme discharge event on plastic transport is still unknown. Here we show that fluvial floods drive macroplastic (>2.5 cm) transport (items h−1) and accumulation (items m−2) in river systems. We collected unique observational evidence during the July 2021 flood along the whole Dutch part ...
Wind- and rain-driven macroplastic mobilization and transport on land
Wind and rain are considered main drivers of mobilization and transport of macroplastics on land,... more Wind and rain are considered main drivers of mobilization and transport of macroplastics on land, yet there is a lack of empirical data that quantifies this. We present lab experiment results on land-based macroplastic mobilization and transport. We placed four types of macroplastics on terrains with varying surface roughness and slope angles, and exposed them to changing wind speeds and rain intensities. In general, we find that the mobilization probability and transport velocity of macroplastics strongly depend on the combination of the terrain characteristics and material properties. At Beaufort 3, 100% of the plastic bags were mobilized, whereas the for the other plastic less than 50% as mobilized. We find higher mobilization probabilities on land (grass: factor 1.5; paved: factor 5) than assumed by existing plastic transport models. Macroplastic transport velocities were positively correlated with wind speed, but not with rain intensity. This suggests that macroplastics are not...
Plastic pollution in rivers is of increased global concern. Rivers act both as pathways for land-... more Plastic pollution in rivers is of increased global concern. Rivers act both as pathways for land-based plastic waste into the ocean, and as plastic reservoirs for long-term retention. Reliable observations are key to designing, optimizing and evaluating strategies to prevent and reduce plastic pollution. Several measurement methods have been developed to quantify macroplastic ($>$0.5 cm) storage and transport in rivers, including visual counting from bridges, net sampling, and images-based techniques. Method harmonization is crucial to make sure data collected using different techniques remains consistent. In turn, this would allow for comparative analysis of plastic pollution within and between rivers. In this paper, we present a harmonization approach to estimate floating plastic item and mass transport from data collected using different methods. The approach allows estimating the same values based on different measurement methods and data collection protocols. We applied our ...
Overcoming Oceans of Ignorance: What You Should Know About Plastic Waste Before It Enters the Sea
WORLD SCIENTIFIC eBooks, 2023
Reducing uncertainty of floating plastic transport estimates in rivers using the visual counting method
&lt;p&gt;Macroplastics have been found in many compartments of freshwater systems amongst... more &lt;p&gt;Macroplastics have been found in many compartments of freshwater systems amongst which floating at the water surface. To quantify the floating macroplastic flux in rivers, the visual counting method was developed. This method is based on visual observations from bridges, and has already been applied in various river systems across the world, including the Rhine-Meuse delta. A two-year dataset of monthly field measurements on ten bridges across the Rhine, Meuse, and IJssel rivers has been collected. This dataset revealed the high variability of the floating macroplastic flux in both time and space. Except for extreme flooding events, the fluctuations are not always simply related to the discharge or season. This finding raises the questions of how to assure representative field observations. Representative field observations are important, as they are typically inter- and extrapolated in time and space. If the timing or location of the measurement is not representative of the &amp;#8216;normal&amp;#8217; condition, then the extrapolation of that measurement will be associated with a large uncertainty range, resulting in over- or underestimations of the total floating macroplastic flux in the river. As field observations play a major role in calibrating and validating river plastic transport and emission models, it is essential to minimize the uncertainty of field-based floating plastic transport estimates. To optimize the visual counting method and explore its limits, we executed three experiments. The first experiment demonstrated that the temporal variability at bridge level is high, but can be attenuated by repeated measurements. The second experiment showed how many observation points on the bridge are sufficient to account for the spatial variability of the macroplastic flux across the river cross profile. The third experiment determined that the size limit of the visible macroplastics is 1 cm&lt;sup&gt;2&lt;/sup&gt; on bridges that are up to 5 meter above water level and 4 cm&lt;sup&gt;2&lt;/sup&gt; for bridges up to 15 meter above water level. The findings of these experiments endorse the effectiveness of the visual counting method and allow for a substantiated implementation of this method in floating macroplastic monitoring campaigns across river networks worldwide.&lt;/p&gt;
Exploring Macroplastic Transport and Retention Dynamics in Country-Wide River Networks
&lt;p&gt;Over the last years macroplastic has been increasingly monitored not only in oce... more &lt;p&gt;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.&lt;/p&gt; &lt;p&gt;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.&lt;/p&gt; &lt;p&gt;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.&lt;/p&gt;
Hydrology as driver of floating river plastic transport
Land-based plastic waste is the major source for freshwater and marine plastic pollution. Yet, th... more Land-based plastic waste is the major source for freshwater and marine plastic pollution. Yet, the transport pathways over land remain highly uncertain. Here, we introduce a new conceptual model to forecast plastic transport on land: the Plastic Pathfinder; a numerical model that simulates the spatiotemporal distribution of macroplastic (>0.5 cm) at a river basin scale. The plastic transport driving forces are wind and surface runoff, while plastic transport is resisted by terrain surface friction. The terrain surface friction, a function of the slope and land use, is converted into thresholds that define the critical wind and surface runoff conditions required to mobilize and transport macroplastic waste. When the wind and/or surface runoff conditions exceed their respective thresholds, the model simulates the transport and (re)distribution of plastics, resulting in plastic accumulation hotspots maps and high probability transport route maps. The Plastic Pathfinder contributes t...
The number of designated Protected Areas (PAs) worldwide has been increasing fast over the past d... more The number of designated Protected Areas (PAs) worldwide has been increasing fast over the past decades and currently 15.1% of the land and 7.9% of the ocean’s surface are under protection. However, the mere designation of a PA does not guarantee any degree of protection. Where the IUCN Categorizing system classifies PAs solely based on the management strategy on paper, the actual effects of this management remain undetermined. Over the past years, thousands of PA effectiveness methodologies have been developed and applied to PAs from all over the world. However, the majority of the existing assessments are not entirely fit for a quick and easy assessment of the actual quality of the protection in place. Therefore, we propose a new method that assesses the effects of the PA management and thereby reflects the actual degree of protection within the borders of a PA. We present the Protection Level Index (PLI), an index (ranging from 0 to 1) that is based on the scores for 12 equally weighted managerial, socio-economic and ecological sub-indices that are based on both the results from a questionnaire and an analysis of the spatial characteristics of the PA in a GIS. One of the great advantages of PLI is that it omits pre-defining universal optimal conditions and instead allows the PA manager(s) to put numerical quantifications into context. PLI has been tested for 7 European PAs covering a wide range of environmental regimes. The results indicate that some the sub-indices are closely related to each other and that despite the dissimilarities between the 7 PAs, they all have a similar final PLI score in the midrange around 0.63. This emphasizes the unbiased character of PLI, which makes it an ideal protected area management effectiveness method that can be applied to any PA worldwide
A practical novel assessment tool for the socio-ecological condition of Protected Areas: The Protection Level Index (PLI)
Journal for Nature Conservation, 2021
Abstract Protected Area (PA) managers and policy makers need to determine and demonstrate the eff... more Abstract Protected Area (PA) managers and policy makers need to determine and demonstrate the effectiveness of PA management and keep track of the conservation status in ways that are practical, scientifically sound and comparable among PAs in various terrestrial and aquatic environments. As most existing methods for measuring the managerial efficiency of PAs are restricted to specific elements of the management or a limited number of detailed environmental aspects, often without the participation of practitioners, we aim for a generally applicable method developed in close cooperation with PA managers; the Protection Level Index (PLI). PLI includes ecological, socio-economic, as well as managerial factors, and consists of twelve variables that together describe the state of a PA. Seven of those are derived from interviews with PA managers, and five of them are derived from GIS analyses. Data were obtained during face-to-face interviews with PA managers using a fixed protocol, thereby introducing a new way of incorporating the perception of the PA managers. PLI was tested in seven different PAs across Europe. The lowest final PLI score was for the Island Network of Protected Areas in La Palma and the highest final PLI score was for the Kalkalpen National Park. PLI is wider applicable than other related methods and more cost-effective. Therefore PLI can be used on a yearly basis to keep track of the progress of management activities and conservation status within and among (networks of) PAs.
Hydrology as a Driver of Floating River Plastic Transport
Earth's Future
Sample size requirements for riverbank macrolitter characterization
River plastic during floods: Amplified mobilization, limited river-scale dispersion
Plastic pollution in the world's rivers and ocean is increasingly threatening ecosystem healt... more Plastic pollution in the world's rivers and ocean is increasingly threatening ecosystem health and human livelihood. In contrast to what is commonly assumed, most mismanaged plastic waste that enters the environment is not exported into the ocean. Rivers are therefore not only conduits, but also reservoirs of plastic pollution. Plastic mobilization, transport and retention dynamics are influenced by hydrological processes, and river catchment features (e.g. land-use, vegetation, and river morphology). Increased river discharge has been associated with elevated plastic transport rates, although the exact relation between the two can vary over time and space. The precise role of an extreme discharge event on plastic transport is however still unknown. Here, we show that fluvial floods drive plastic transport and accumulation in river systems. We collected unique observational evidence during the July 2021 flood along the complete Dutch part of the Meuse. Plastic transport multipli...
How gravity, wind, rain and surface runoff drive plastic transport on land
&amp;amp;lt;p&amp;amp;gt;To accurately predict the transport routes of mismanaged plastic... more &amp;amp;lt;p&amp;amp;gt;To accurately predict the transport routes of mismanaged plastic waste from land-based sources to their sinks, terrestrial plastic transport models require a robust empirical basis. The main driving forces behind the transport of macroplastics on land are assumed to be gravity, wind, rain and surface runoff. However, the underlying transport principles remain undescribed and unresolved. To determine the minimum wind velocities, rainfall, and surface runoff that are required to mobilize and transport macroplastic items, physical laboratory experiments on an artificial hillslope were performed. Four types of macroplastic waste items were used (bottles, cups, food packaging, and bags) while surface roughness (concrete versus grass) and slope angles (0&amp;amp;amp;#176;, 10&amp;amp;amp;#176;, 20&amp;amp;amp;#176;) were systematically varied. Here we present the identified wind, rain and surface runoff thresholds, as well as the relations between the wind velocity and the plastic transport velocity. These thresholds and relations can be implemented in terrestrial plastic transport models to forecast the transport and (re)distribution of macroplastic waste on land due to wind, rain and surface runoff. The overland pathways simulated by these models, reveal where macroplastic retention occurs on land, and where terrestrial macroplastics enter waterbodies. The locations of the terrestrial accumulation zones, and the main entry points into waterbodies are crucial input for the design of mitigation and prevention measures.&amp;amp;lt;/p&amp;amp;gt;
Rivers as Plastic Reservoirs
&amp;amp;lt;p&amp;amp;gt;Land-based plastic waste, carried to the sea through rivers, is ... more &amp;amp;lt;p&amp;amp;gt;Land-based plastic waste, carried to the sea through rivers, is considered a main source of marine plastic pollution. However, most plastics that leak into the environment never make it into the ocean. Only a small fraction of plastics that are found in the terrestrial and aquatic compartments of river systems are emitted, and the vast majority can be retained for years, decades, and potentially centuries. In this presentation we introduce the concept of river systems as plastic reservoirs. Under normal conditions, hydrometeorological variables (such as wind, runoff and river discharge) mobilize, transport and deposit plastics within different river compartments (e.g. riverbanks, floodplains, lakes, estuaries). The emptying of these plastic reservoirs primarily occurs under extreme hydrological conditions (e.g. storms, floods). We specifically focus on the retention mechanisms within different river compartments, and their effect on the fate of the plastics that are accumulated over various timescales. With this presentation, we aim to introduce the concept of rivers as (long-term) sinks for plastic pollution, and provide suggestions for future research directions.&amp;amp;lt;/p&amp;amp;gt;
16,000 riverbank litter items – A data driven approach to optimizing riverine plastic monitoring
&amp;lt;p&amp;gt;Macrolitter in aquatic environments is an emerging environmental risk, a... more &amp;lt;p&amp;gt;Macrolitter in aquatic environments is an emerging environmental risk, as it negatively impacts ecosystems, endangers aquatic species, and causes economic damage. One of the major reservoirs of macrolitter in aquatic environments are riverbanks. To effectively clean riverbanks and prevent future litter from accumulating in these reservoirs, robust monitoring techniques are needed that allow for quick, but reliable, assessments of the type, size and mass of macrolitter in these reservoirs. Here, we present a unique dataset of more than 16,000 anthropogenic litter items in the Dutch Rhine, Meuse and IJssel rivers. With this dataset, we facilitate making considered decisions for developing future monitoring strategies. Items were collected on 8 different riverbanks once per month for one year. Items were collected at upstream and downstream locations along the Dutch part of the rivers, and were categorized (river-OSPAR), weighed and measured. The dataset shows that the majority of the found items is plastic, especially fragments of foam, soft plastics (foils), and hard plastics. The composition of litter type varies more in space than in time, indicating that the spatial resolution of a future monitoring campaign outweighs the importance of the temporal resolution. We performed a Monte Carlo analysis to determine sample size requirements to calculate a representative number of average item mass. Up until 8,900 items are needed for an accurate representation of average items mass, depending on item category uniformity. Finally, a method is proposed to determine on which item size should be focused. The presented dataset can be used in future research, modelling practices and development of management strategies.&amp;amp;#160;&amp;lt;/p&amp;gt;
Land-based plastic waste, carried to the sea through rivers, is considered a main source of marin... more Land-based plastic waste, carried to the sea through rivers, is considered a main source of marine plastic pollution. However, most plastics that leak into the environment never make it into the ocean. Only a small fraction of plastics that are found in the terrestrial and aquatic compartments of river systems are emitted, and the vast majority can be retained for years, decades, and potentially centuries. In this perspective paper we introduce the concept of river systems as plastic reservoirs. Under normal conditions, hydrometeorological variables (such as wind, runoff and river discharge) mobilize, transport and deposit plastics within different river compartments (e.g., riverbanks, floodplains, lakes, estuaries). The emptying of these plastic reservoirs primarily occurs under extreme hydrological conditions (e.g., storms, floods). In this paper we specifically focus on the retention mechanisms within different river compartments, and their effect on the fate of the plastics that...
Plastic pollution in terrestrial and aquatic ecosystems is of growing global concern due to its n... more Plastic pollution in terrestrial and aquatic ecosystems is of growing global concern due to its negative impact on environmental health and human livelihood. Most plastic research to date focused on observing and modelling plastic in the oceans, revealing that the highest plastic concentrations are found in the five ocean gyres (“the garbage patches”). Plastic waste originating from land has been identified as the main source of marine plastic debris. Yet it remains highly uncertain which processes control the mobilisation and transport of plastic waste over land to rivers and eventually to the ocean. Here, we introduce the Trash Tracker, a numerical model to forecast the pathways and fate of plastic waste in terrestrial and freshwater systems. In this model, the plastic transporting agents, wind and surface runoff, are resisted by the friction of the terrain. The terrain resistance, a function of the surface slope and the type of land use, is translated to thresholds that define th...
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Papers by Yvette Mellink