Litter Loads Research Articles

Prescribed fire regimes influence responses of fungal and bacterial communities on new litter substrates in a brackish tidal marsh.

Processes modifying newly deposited litter substrates should affect fine fuels in fire-managed tidal marsh ecosystems. Differences in chemical composition and dynamics of litter should arise from fire histories that generate pyrodiverse plant communities, tropical cyclones that deposit wrack as litter, tidal inundation that introduces and alters sediments and microbes, and interactions among these different processes. The resulting diversity and dynamics of available litter compounds should affect microbial (fungal and bacterial) communities and their roles in litter substrate dynamics and ecosystem responses over time. We experimentally examined effects of differences in litter types produced by different fire regimes and litter loads (simulating wrack deposition) on microbial community composition and changes over time. We established replicated plots at similar elevations within frequent tidal-inundation zones of a coastal brackish Louisiana marsh. Plots were located within blocks with different prescribed fire regimes. We deployed different measured loads of new sterilized litter collected from zones in which plots were established, then re-measured litter masses at subsequent collection times. We used DNA sequencing to characterize microbial communities, indicator families, and inferred ecosystem functions in litter subsamples. Differences in fire regimes had large, similar effects on fungal and bacterial indicator families and community compositions and were associated with alternate trajectories of community development over time. Both microbial and plant community compositional patterns were associated with fire regimes, but in dissimilar ways. Differences in litter loads introduced differences in sediment accumulation associated with tidal inundation that may have affected microbial communities. Our study further suggests that fire regimes and tropical cyclones, in the context of frequent tidal inundation, may interactively generate substrate heterogeneities and alter microbial community composition, potentially modifying fine fuels and hence subsequent fires. Understanding microbial community compositional and functional responses to fire regimes and tropical cyclones should be useful in management of coastal marsh ecosystems.

Understanding the sources of marine litter in remote islands: The Galapagos islands as a case study

Determining the sources of marine litter is necessary to mitigate this increasing global problem. Plastic bottles are useful tracers of marine litter and constitute the main item (24%) stranding on remote beaches in the Galapagos Islands. The aim of this study was to estimate the abundance of plastic bottles in remote beaches and inferred their sources. To do so, we collected plastic bottles at 60 remote Galapagos Island beaches from 2018 to 2022. 76% of beaches were qualified as badly polluted, with >34 bottles·100 m−1. Most identified bottles came from Peru (71%), followed by China (17%) and Ecuador (9%). Although most locally-sold products are made in Ecuador, they contribute little to beach litter loads. Polyethylene terephthalate bottles with lid (necessary for litter dispersal) represented 88% of all bottles, demonstrating that most of the litter reaching the Galapagos comes from distant sources, mainly from South America. However, bottle ages indicate that at least 10% of Peruvian, 26% of Ecuadorian, and all Chinese bottles likely were dumped from ships. Reducing marine litter reaching the Galapagos Islands requires tackling litter leakage from land-based sources in South America and better compliance with regulations banning the dumping of plastics and other persistent wastes from ships.

Land-derived litter load to the Indian Ocean: a case study in the Cimandiri River, southern West Java, Indonesia.

The first study related to the characteristics of the riverine litter was carried out at the mouth of the Cimandiri River in the southern West Java to provide a national database, as mandated in the Indonesian Presidential Regulation 83/2018 concerning the handling of marine debris. We examined floating riverine litter entering the South Java Sea at Cimandiri River outlets four times between December 2020 and October 2021 using a Thomsea 1T trawl-net. The amount of litter collected tended to rise throughout the sampling period. Daily floating riverine litter released into the South Java Sea was estimated to be 285,931 ± 133.70 items or 307 ± 192.69kg. Our monitoring data revealed no sampling period differences in litter release into the South Java Sea with no correlation with rainfall. Our data indicate that plastics are the most single abundant type of floating riverine litter entering the South Java Sea from the Cimandiri River, accounting for 99.92% of abundance (285,701 ± 133,464.75 items per day) or 97.78% in terms of weight (300 ± 181.99kg per day) of the total litter collected. As the Cimandiri River is one of the major rivers with an outlet in the south of Java, this land-derived litter information could be an archetype for riverine ecosystems in the nation and region.

Dune plants as a sink for beach litter: The species-specific role and edge effect on litter entrapment by plants

Anthropogenic litter accumulates along coasts worldwide. In addition to the flowing litter load, wind, sea currents, geomorphology and vegetation determine the distribution of litter trapped on the sandy coasts. Although some studies highlighted the role of dune plants in trapping marine litter, little is known about their efficiency as sinks and about the small-scale spatial distribution of litter across the dune area. Here, we explore these gaps by analysing six plant species widespread in Mediterranean coastal habitats, namely Echinophora spinosa, Limbarda crithmoides, Anthemis maritima, Pancratium maritimum, Thinopyrum junceum, and Salsola kali. The present study analyses for the first time the capture of litter by dune vegetation at a multi-species level, considering their morphological structure. Data on plastic accumulation on dune plants were compared with unvegetated control plots located at embryo-dune and foredune belts. We found that dunal plants mainly entrapped macrolitter (> 0.5 cm). Particularly, E. spinosa, L. crithmoides, A. maritima and P. maritimum mostly accumulated litter in the embryo dune while T. junceum and S. kali entrapped more in the foredune area. Moreover, beach litter was mainly blocked at the edge of the plant patches rather than in the core, highlighting the ‘Plant-edge litter effect’. As A. maritima and S. kali entrapped respectively more litter in embryo and foredune habitats, these species could be used to monitor and recollect litter. In this light, our findings provide further insight into the role of dune plants in the beach litter dynamics, suppling useful information for beach clean-up actions.

Implementing land-based litter surveys through visual inspection of imagery using unmanned aerial vehicles

Understanding the location of dumping sites, or where littering occurs, is needed for effective and efficient waste management efforts. South Africa experiences open indiscriminate dumping and faces a challenging social practice of littering. This pilot study used unmanned aerial vehicle imagery, aimed to monitor litter loads (illegal dumps and individual littered items) over a large land area (> 2 km2) to assess potential change in litter through time. Two techniques, the Percentage Cover Technique and the Comparison Technique, were used. The two techniques were trialed at five sites to quantify litter load and monitor change over time. Overall, through the Percentage Cover Technique, 13.5% of the study area was covered in litter in February 2020, and this decreased to 10.3% by July 2021. All five sites individually showed a decrease in litter loads, with significant differences between imagery sets (H(2) = 52.786, P < 0.001) and between surveyors (U = 15 567 399, n1=n2=5 211, P < 0.001 two-tailed). The Comparison Technique revealed that of the 10 422 blocks analysed in this study, litter coverage decreased in 10.3% and increased in 8.3%, of them. The study showed that the Comparison Technique is an easy and inexpensive method to monitor litter loads on large scales and could therefore be replicated across Africa which has limited resources (financial and expertise).

A spatially explicit model of tree leaf litter accumulation in fire maintained longleaf pine forests of the southeastern US

The continuity and depth of litter fuelbeds are major drivers of fire spread and fuel consumption. However, no established approach is available for the spatially explicit prediction of litter loads over large areas. Local fuel heterogeneity introduces large uncertainties on estimates derived from field-based models based on the extrapolation of sparse data samples. In fire-maintained pine forests of the southeastern US, litter accumulation and its distribution over the forest floor are mainly driven by vegetation productivity and by the number of years since the last fire (YSF). Some ecological models that simulate fire effects allow for a time-dependent estimation of litter by accounting for the opposing rates of litter deposition and decomposition as a function of YSF at the landscape level, but they do not account for spatial heterogeneity. We developed a conceptually simple approach for wall-to-wall estimation of tree leaf litter loads at high spatial resolution (5 m). The approach involved, first, estimating spatial patterns of tree annual litterfall. We mapped individual tree crowns through segmentation of airborne laser scanning (ALS) data, and we estimated crown foliage biomass using tree inventory data and ALS derived tree crown attributes. Tree annual litterfall was calculated as a fraction of the crown foliage biomass based on leaf turnover rates. We then quantified tree leaf litter accumulation through a spatially explicit implementation of the established Olson (1963) accumulation and negative decay model. We tested and validated our model in several management and research units at Eglin Air Force Base (Florida), Pebble Hill Plantation (Georgia), and Osceola National Forest (Florida), where managers maintain predominantly longleaf pine forests using frequent fire. Pixel-level RMSD and BIAS between tree leaf litter biomass estimated by the proposed model and reference field measurements were 0.21 and 0.01 kg m−2, and area-level RMSD and BIAS were 0.09 and 0.01 kg m−2. We concluded that linking patterns of litterfall and tree leaf litter accumulation to tree crown objects provides a means to characterizing the discontinuity of the litter layer, accounting for spatial heterogeneity largely traceable to tree crown foliage inputs.

Proximity to coast and major rivers influence the density of floating microplastics and other litter in east African coastal waters

Floating anthropogenic litter occurs in all ocean basins, yet little is known about their distribution and abundance in the coastal waters off east Africa. Neuston net and bulk water sampling shows that meso- and micro-litter (8567 ± 19,684 items∙km−2, 44 ± 195 g∙km−2) and microfibres (2.4 ± 2.6 fibres∙L−1) are pervasive pollutants off the coasts of Tanzania and northern Mozambique, with higher litter loads off Tanzania. Densities of meso- and micro-litter at the start of the rainy season were greater close to the coast and to major river mouths, suggesting that much litter likely originates on land. However, the mass of litter increased with distance from the six major coastal cities. By number, 95% of meso- and micro-litter was plastic, but only 6% of microfibres. Our results highlight the need to reduce plastic use and improve solid waste management in the region.

Comparative analysis of fuel loads in the area affected by fire and without fire in Malinaltepec, Guerrero

Forest fires are one of the factors that contribute to climate change, among the components that form the fire triangle, fuel is theonly factor that can be manipulated. The objective of this work was to estimate the load of forest fuels in Mg ha-¹ in an area burnedin 2015 and another area without fire. For the evaluation of forest fuel, three sampling sites were established in each of the areas,the woody material was counted by delay time (1, 10, 100 and 1000 h) according to the technique of planar intersections; at the endof each line, litter (h) and mulch (m) were collected in 0.09 m². Tests were carried out to contrast the general fuel load and by typebetween ecosystems; Tukey's means comparison test was used to contrast the fuels in a given area, finally the woody material (ml),mulch (m) and litter (h) were correlated with the total load (ct), litter depth (ph) and mulch depth (ph) using Pearson correlationtests. The total fuel load was 53.10 Mg ha-¹ in the burned area, while the area without fire showed a load of 27.26 Mg ha-¹ withoutsignificant differences (p = 0.114). On the comparison of loads by delay time, the fuel of 1, 10 and 100 h showed a higher load inthe burned area, although it was not significant (p &gt; 0.05); the analysis by component showed a higher litter load in the non-burnedarea with 12.90 Mg ha-¹ (p = 0.015) and the woody material was statistically higher in the burned area with 35.95 Mg ha-¹ (p =0.024). The correlation of variables showed an r = 0.95 between the woody material and the total load; followed by leaf litter andmulch (r = 0.80); on the contrary, the total load in the non-burned area showed a correlation with the mulch and leaf litter (r = 0.89and 0.83). The forest fire contributed to the reduction of litter and mulch but maximized the load of woody fuel.

Abundance, composition and sources of beach litter on the Cape Verdean island São Vicente.

This study represents the first assessment of beach litter on an island of the west African archipelagic state of Cape Verde. On five beaches of São Vicente, litter was collected along transects and classified according to the OSPAR protocol, with the Matrix Scoring Technique used to allocate it to four sources. Beach litter on São Vicente is highly variable in both amount and composition, while land- and sea-based sources contribute to litter loads to different extents depending on the use and geographic orientation of the beach. Four of the five surveyed beaches exhibited litter loads that were similar to pollution levels previously described for other oceanic islands, while a north-eastern-facing beach featured exceptionally high loads. This was presumably because it receives litter from distant sources due to its exposure to a major ocean surface current.

Litter, Plant Competition, and Ecosystem Dynamics: A Theoretical Perspective.

AbstractCommunity structure depends jointly on species' responses to, and effects on, environmental factors. Many such factors, including detritus, are studied in ecosystem ecology. Detritus in terrestrial ecosystems is dominated by plant litter (nonliving organic material), which, in addition to its role in material cycling, can act as a niche factor modulating interactions among plants. Litter thus links traditional community and ecosystem processes, which are often studied separately. We explore this connection using population dynamics models of two plant species and a litter pool. We first find conditions determining the outcome of interactions between these species, highlighting the role that litter plays and the role of broader ecosystem parameters, such as decomposition rate. Species trade-offs in tolerance to direct competition and litter-based interference competition allow for coexistence, provided the litter-tolerant species produces more litter at the population level; otherwise, priority effects may result. When species coexist, litter-mediated interactions between plants disrupt the traditional relationship between biomass accumulation and decomposition. Increasing decomposition rate may have no effect on standing litter density and, in some cases, may even increase litter load. These results illustrate how ecosystem variables can influence community outcomes that then feed back to influence the ecosystem.

Standing stock and daily accumulation of beach litter in KwaZulu-Natal, South Africa

Beach litter accumulation studies are an important method to investigate litter flows to the marine environment. We detail a standing stock and daily accumulation study, conducted at two locations approximately 20 km north (uMhlanga) and south (Amanzimtoti) of the Port of Durban, South Africa. The materials collected were dominated in number by plastic, which constituted more than 90% of all items found during the surveys. Accumulation ranged from 134 to 719 items 100 m−1 d−1, falling within the range of similar studies in South Africa. Accumulation weights (wet and uncleaned, WU) ranged from 0.10 to 2.49 kg per day. Between the two sites, standing stock per 100 m ranged between 921 to 1534 items, and between 1.06 to 4. 03 kg(WU). Overall, higher litter loads were observed at Amanzimtoti beach compared to uMhlanga beach. Our statistical modelling showed that litter numbers varied by beach, whether collection was above or below high tide and the amount of rainfall. At Amanzimtoti, more litter was found above the tide line throughout the study, but at uMhlanga, this was only true for the first part of the study. Analysis of the types of litter found between beaches, suggest different sources of litter that could be used to tailor waste management solutions in each local area. Greater numbers of cotton bud sticks found at uMhlanga, suggests sewage treatment outputs contribute to the litter loads in this area, while large amount of linoleum flooring fragments found at Amanzimtoti suggest construction could be the source.

Environmental context and socio-economic status drive plastic pollution in Australian cities

Plastic pollution is a critical environmental concern. There is a growing focus on this transboundary issue, and a corresponding increase in public and government awareness. Understanding the key factors associated with litter and mismanaged waste on land will help to predict where and how waste enters the environment, providing opportunities for low cost, effective interventions. There exist only a few large-scale datasets with which such analyses can be conducted. To fill this knowledge gap we analysed a national, designed survey dataset of litter in the environment from Keep Australia Beautiful (2007–2017). We found that debris decreased significantly, with a nearly 6% decrease over the decade. Using generalised additive model modelling of 17 653 surveys at 983 sites around Australia, we found that site type, land use, state, population, and socio-economic status had the strongest relationships (in decreasing order) with litter distribution. Higher levels of litter were found in economically and socially disadvantaged neighbourhoods. Site types related to transitory human use such as highways and carparks, had more litter than areas with higher aesthetic or cultural value such as beaches, parks, and residential neighbourhoods. Sites that were sources of litter, such as shopping centres and retail strips, also had elevated litter counts, as did surveys near waterways. This enhanced understanding of the factors that influence litter deposition will help to craft more effective policy solutions, and can also improve our models of litter loads on land, and subsequent input to the ocean.

A baseline study of macro, meso and micro litter in the Belize River basin, from catchment to coast

Abstract The mismanagement of waste and subsequent presence of litter in the environment is an increasingly significant problem. Globally, rivers have been shown to be a major pathway for mismanaged waste. We investigated the distribution of macro, meso and micro litter along the Belize river basin. The North-East Atlantic OSPAR beach litter monitoring protocol was adapted for Belize, taking into account local issues such as mangroves and Sargassum sp. accumulations. On average, 77.3% of litter items consisted of plastic, and the most common items categories were unidentifiable plastic pieces (0–2.5 and 2.5–50 cm), broken glass, and metal bottle caps. The study indicated that there is an increase in the litter load as you move from catchment to coast, with both Plastic Pieces (PP) and Fishing Related (FR) items also increasing in numbers down the system. Additionally, microplastics abundance was determined in riverine sediments and in the riverine fish Cichlasoma synspilum (n = 22). All sediment samples contained microplastics, with a concentration of 200–6500 particles per kg dry sediment. Microplastics were found to be present in 36% of the riverine fish. The data from this study will provide evidence for the formation of Belizean legislation to reduce marine litter.

Modelling aboveground biomass and fuel load components at stand level in shrub communities in NW Spain

Shrub-dominated ecosystems cover large areas globally and play essential roles in ecological processes. Aboveground biomass expressed on an area basis (AGB) is central to many of the ecological processes and services provided by shrublands and is important as the main fuel source for wildfires. Hence, its accurate estimation in shrublands is crucial for ecologists and land managers. This is especially relevant in fire-prone regions such as NW Spain, where shrublands are an important part of the landscape, providing multiple services, but are severely impacted by wildfires. Although biomass models are available for numerous shrub species at the individual plant level, operational models based directly on easily measured shrub stand attributes are scarce. In this study, equations for estimating AGB and loads of different fuel components by size and condition (live and dead) from stand biometric variables were developed for the nine most prevalent shrub communities in NW Spain. Non-linear iterative seemingly unrelated regression was used to fit compatible systems of equations for estimating fuel loads, with shrub stand height and cover and litter depth as predictors for individual shrub communities and all data combined. In general, the goodness-of-fit statistics indicated that the estimates were reasonably accurate for all communities (grouped and ungrouped). The best results were obtained for AGB and total fuel load, including litter, whereas the poorest results were obtained for standing live and dead fine fuel load. Model performance was reduced when height was the only independent variable, although the reduction was small for most fuel categories, except litter load for which the variability was adequately explained by the litter depth. These results illustrate the feasibility of the stand level approach for constructing operational models of shrub fuel load that are accurate for most of fuel components, while also highlighting the ongoing challenges in live and dead fine fuel modelling. The equations developed represent an appreciable advance in shrubland biomass assessment in the region and areas with similar characteristics and may be instrumental in generating fuel maps, fire management improvement and better C storage assessment by vegetation, among other many uses.

Message in a bottle: Assessing the sources and origins of beach litter to tackle marine pollution

Beaches are key attractions for tourism and recreation, and considerable effort is made to keep beaches clean, yet many beaches still have substantial litter loads. Lasting solutions to reduce the amounts of marine litter require an understanding of litter sources. We collected bottles and other single-use containers at 32 sites around the South African coast to infer their sources based on their age and country of manufacture. Bottle densities varied greatly among beaches (8–450 bottles·km−1), depending on proximity to local urban centres and beach cleaning frequency. Most bottles were plastic, despite well-developed recycling initiatives for PET and HDPE bottles in South Africa. Street litter was dominated by bottles made in South Africa (99%), but foreign-manufactured bottles comprised up to 74% of bottles at some beaches, with an increase from urban (4%) through semi-urban (24%) to remote beaches (45%). Most foreign bottles were PET drink bottles from China and other Asian countries, followed by South America and Europe, with little regional variation in the contribution from these sources. This fact, coupled with their recent manufacture dates (mainly <2 years old), indicates that most foreign PET drink bottles are dumped illegally from ships. By comparison, foreign HDPE bottles were more common along the southeast coast of South Africa than along the west coast, consistent with many of these bottles arriving by long-distance drift across the Indian Ocean from southeast Asia. The most common country of origin for these bottles was Indonesia, and most newly-arrived HDPE bottles were 4–6 years old. To tackle beach litter in South Africa we need to greatly reduce plastic leakage from land-based sources, both locally and in southeast Asia, as well as improve measures to prevent the illegal dumping of plastics and other persistent wastes from ships.

Long-term impacts of silvicultural treatments on wildland fuels and modeled fire behavior in the Ridge and Valley Province, Virginia (USA)

Active forest management operations, such as regeneration harvests, can reduce hazardous fuel loads and alter fuel structure, potentially minimizing extreme wildfire conditions while maintaining ecosystem services, such as wildlife habitat and water quality. Regeneration harvests of differing intensities (clearcut, high-retention shelterwood, and low-retention shelterwood) were first applied between 1995 and 1996 to three sites on the George Washington-Jefferson National Forest in the Ridge and Valley Province of Virginia, USA. Over two decades after the clearcut was conducted and 11–12 years after the overwood was removed in the shelterwood stands, woody debris, litter, and duff masses and depths were quantified. One-hour fuel loads were greater in clearcut units than in high-retention shelterwood, low-retention shelterwood, or control units. Ten-hour fuel loads were greater in clearcut and low-retention shelterwood units than in high-retention shelterwood and control units. No significant differences in 100-hour fuels were observed between treatments. Control units contained more rotten and total 1000-hour fuels than all other treatments. The total woody debris load was less in the clearcut and high-retention shelterwood than in the low-retention shelterwood and control. High-retention shelterwood woody fuel depth was greater than clearcut woody fuel depth. Litter and duff loads were less in treated units than in the control units. Total fuel load (woody fuel load + litter load + duff load) was greater in the control than the silvicultural treatments. Litter depth did not differ between treatments, while duff depth was greater in the control than in the treated units. Using the computer modeling software, BehavePlus 6.0.0, these alterations to fuel loads and depths led to increased values in the control units for six fire behavior parameters. Predicted surface flame length in the low-retention shelterwood was the only modeled value that was not less than control values. Overall, these results indicated that harvest intensity and timing may have long-term effects on down and dead woody fuels, forest floor depth, and potential fire behavior. Clearcutting reduced fire behavior most, followed by the high-retention shelterwood system. The potential differences in slash and debris generated by varying shelterwood systems may impact long-term fuel and fire dynamics.

Floating macrolitter leaked from Europe into the ocean

Riverine systems act as converging pathways for discarded litter within drainage basins, becoming key elements in gauging the transfer of mismanaged waste into the ocean. However, riverine litter data are scarce and biased towards microplastics, generally lacking information about larger items. Based on the first ever database of riverine floating macrolitter across Europe, we have estimated that between 307 and 925 million litter items are released annually from Europe into the ocean. The plastic fraction represented 82% of the observed litter, mainly fragments and single-use items (that is, bottles, packaging and bags). Our modelled estimates show that a major portion of the total litter loading is routed through small-sized drainage basins (<100 km2), indicating the relevance of small rivers, streams and coastal run-off. Moreover, the major contribution of high-income countries to the macrolitter inputs suggests that reducing ocean pollution cannot be achieved only by improving waste management, but also requires changing consumption habits and behaviour to curb waste generation at source. The inability of countries with well-developed recovery systems to control the leakage of waste into the environment further supports the need to regulate the production and use of plastic on a global scale. Riverine systems help transfer mismanaged waste into the ocean, but riverine litter data are scarce. Using a database of riverine floating macrolitter across Europe, this study estimates that 307–925 million litter items—82% of which is plastic—are transferred annually from Europe into the ocean.

Influence of hydrological runoff and catchment characteristics on accumulation floatable litter load in gross pollutant trap (GPT)

The accumulation of floatable litter load captured in gross pollutant trap (GPT) due to the hydrological runoff has become challenging due to rapid development and alteration of land use changes. The application of soil conservation service curve number (SCS-CN) method has been widely used to estimate the direct runoff from the given rainfall especially when there is no runoff measured within the catchment. The results found that there was enormous variation on floatable litter load between different months and individual GPT. There was a high accumulation of floatable litter load on August 2015 with 495 kg/month and at K17 with 510 kg. Both of these conditions was significantly influenced by rainfall depth, hydrological parameters such as initial abstraction, potential maximum retention, and average weighted curve number (CNaw) values from different types of land use within their respective catchment area for individual GPT. Thus, the outcomes from this study can be very useful and beneficial for related government agencies and various stakeholders in ameliorating this critical and challenging environmental issue in terms of operation and management; technical operation; the selection of GPT prior to installation in other areas including the design, costs and maintenance.

Microplastic abundance in beach sediments of the Kiel Fjord, Western Baltic Sea

We assessed the abundance of microplastics (0.2–5 mm) in drift line sediments from three sites in Kiel Fjord, Western Baltic Sea. The first site is intensively used by beach visitors, the second is in close proximity to a sewage plant and the third is polluted with large-sized plastic litter. Samples were split into three grain size classes (0.2–0.5, 0.5–1, 1–5 mm), washed with calcium chloride solution, and filtered at 0.2 mm. Filters were then visually inspected, and a total of 180 fragments was classified as microplastics, of which 39% were analyzed using Raman spectroscopy. At the site that is close to a sewage plant as well as at the site with intense beach use, 1.8 and 4.5 particles (fibers plus fragments) per kg of dry sediment were found, respectively, while particle abundances reached 30.2 per kg of dry sediment at the site with high litter loads. Our data suggest that the fragmentation of large plastic debris at site seems to be a relevant source for microplastics in Western Baltic Sea beach sediments.

Limited dispersal of riverine litter onto nearby beaches during rainfall events

Rivers are assumed to be one of the major conduits for plastics entering the sea, but little is known about the interchange of plastic litter between rivers and coastal waters. We measured the amount of litter stranding on the beach around the mouth of a seasonal river in Cape Town, South Africa, to infer litter dispersal distances. Prior to the mouth opening, litter was fairly uniformly distributed along the 2.4 km study beach. Once the mouth was opened for the first major winter storm, most litter stranded within 0.5 km of the river mouth. Beach litter loads peaked during rain events and decreased after the first rainfall event, presumably due to flushing of accumulated litter in the coastal wetland. However, litter loads within the wetland remained high, indicating that only a proportion of litter flushes during floods. Experimental deployments of marked litter items confirmed that most floating litter strands close to the mouth, although less buoyant items travelled farther than more buoyant items. Exchanges occurred in both directions, with marine litter found up to 1.2 km inland in the estuary. On a rising tide, more litter items moved into the estuary than into the sea, despite strong offshore winds. Our results illustrate the complex interplay of litter between rivers and the sea, and suggest that a large proportion of floating litter carried down small rivers washes ashore shortly after entering the sea. Cleaning beaches around river mouths, especially after rain events, will help to reduce leakage of plastic from land-based sources into the sea.