Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences最新文献

The article investigates the interaction between the sea-breeze circulation and the urban heat island effect in Houston, Texas, located on the Gulf of Mexico coast. The analysis focuses on the summer period in 2022 during the Convective-cloud Urban Boundary-layer Experiment and the Tracking Aerosol Cloud Convection Interactions Experiment. The work, which exclusively used ground-based observations, found a high degree of intra-urban variability in both the temperature and the humidity field during the sea-breeze days. Near-surface virtual potential temperature during the sea-breeze episodes in the metropolitan area varied by almost 10 K, with urban regions near the coast experiencing lower temperature than the inland region. The urban heat island effect was strong enough to create persistent hot spots even during the sea-breeze episodes. On land-breeze days, both the temperature and the humidity fields were more uniform with little spatial variability. The depth of the sea-breeze circulation was captured using X-band radar and radiosondes; it averaged around 1500-2000 m above ground level. The thermal gradient due to the interaction between the sea-breeze circulation and the urban heat island effect led to secondary flows that influenced local convective activity.This article is part of the theme issue 'Urban heat spreading above and below ground'.

Rivers polluted by plastics have become sites where mixtures of microplastics and sediment particles are transported by the river current and deposited in the riverbed. A hydromorphodynamic numerical model was developed using Delft3D (software specialized in simulating natural water systems), to simulate the sedimentation, erosion, resuspension and transport of microplastics together with sediment particles, introducing an innovative model with an active riverbed. The model was used to understand the distribution patterns, morphological changes and load balances of plastic debris in a river. The study case is an artificial braided river with a non-buoyant suspended microplastic load. The results simulate a sediment bed that acts as a source of microplastic storage near the point of release. The high deposition of microplastics increases the capacity of the river flow to erode the banks and channels, resulting in deeper channels and larger river bars. The highest amounts of microplastics were deposited in the inner channel banks, and the highly suspended microplastic load is transported in the main channel thalweg. The model can be used as a more accurate method to predict the dynamics of microplastic fluxes in rivers, providing better tools to understand how much plastic enters the ocean from the river environment.This article is part of the Theo Murphy meeting issue 'Sedimentology of plastics: state of the art and future directions'.

Seafloor sediments have been defined as sinks for microplastics in the marine environment and could therefore represent suitable matrices for their long-term monitoring. Previous studies indicated the widespread distribution of microlitter in seafloor sediments for the UK. In the present study, observations from 2017 to 2021 were used to produce a microlitter distribution model (unitless), derived from physical properties of the seabed that are known to drive the storage capacity of microlitter. The predicted distribution model was converted into a geospatial data layer and plotted against additional open access data layers for likely sources of marine litter (e.g. marine structures) as well as data layers for more sensitive features around the UK (e.g. marine protected areas (MPAs)). Visualization of the accumulation zones for microlitter against the different layers allowed the identification of areas potentially at risk from an increased addition of microlitter from various sources (e.g. dredge disposal sites). Identification of potential risks and prioritization for different zones of action would help the development of national and regional monitoring strategies while reducing costs of multi-compartment, larger scale monitoring programmes. Additional observations and targeted monitoring data are needed to link potential sources of accumulations for microplastics with a higher level of certainty.This article is part of the Theo Murphy meeting issue 'Sedimentology of plastics: state of the art and future directions'.

Urban rivers are hypothesized to be major transporters of plastic pollution into lakes and oceans, with storm events playing a pivotal role. However, few studies investigate microplastic and macroplastic contamination and transport across a river basin, and how it varies with flow. Here, we sampled microplastic (less than 5 mm) and macroplastic (greater than 5 mm) from four sites along an urban river in Ontario, Canada, during baseflow and stormflow. To contextualize their fate and transport through river reaches, we sampled macroplastic stored in the riparian zone, overhanging vegetation, floating in surface water and riverbed and sampled microplastic from the surface water, water column and sediment. At baseflow, most macroplastic was found in the riparian zone (ranging from 0.1 to 4.7 pieces per m²). During stormflow, concentrations (micro and macro) rise and fall with discharge. Moreover, the composition of microplastics in the water column shifts from fibre- to rubber-dominated during higher flows. The mobilization of denser (e.g. rubber) particles during flow is consistent with greater water velocities during storms. Finally, using our data and flow patterns from 2022 to 2023, we estimate that approximately 522 billion microplastic particles and 20 754 macroplastic items, equalling approximately 36 000 and 160 kg by mass, respectively, are transported to Lake Ontario annually.This article is part of the Theo Murphy meeting issue 'Sedimentology of plastics: state of the art and future directions'.

This study examines the distributions and dynamics of litter accumulation in a part of the northeastern coast of Sicily, southern Italy, using a multidisciplinary approach with manned and unmanned aerial systems imagery, a machine-learning algorithm and analysis of meteorological data. Aerial imagery shows that litter accumulations are present on beaches near the river mouths and potentially after flash floods. At least five distinct flash flood events depositing litter have been inferred since March 2015 to January 2024 in the study area. Meteorological data show that high precipitation, resulting in flash floods, and prevailing wind direction from the sea are the primary contributors to litter accumulation in this area. The algorithm applied on drone imagery on one of the accumulations detected a composition of polystyrene (42.6%), wood (35.6%), polyurethane (6.1%) and polyethylene terephthalate (5.4%). The general composition of the litter accumulation and its distribution near river mouths suggests that its source is associated with the input from nearby towns through mismanagement on the riverbeds, followed by flash floods. This study highlights the importance of considering river floods when investigating litter dynamics in coastal environments, as well as the potential of using aerial imagery and machine learning to help assess this problem.This article is part of the Theo Murphy meeting issue 'Sedimentology of plastics: state of the art and future directions'.

Microplastics are an anthropogenic contaminant widely recognized for their effect on marine and freshwater systems, but their terrestrial effects remain less well studied. The inclusion of microplastics in soils has the potential to affect a range of different soil properties, including bulk density, hydraulic conductivity and aggregation. Soil properties affect the susceptibility of soils to wind erosion, and it is therefore likely that where the quantity of microplastics present in soils is sufficient to change soil properties, it may also change the response of soils to wind erosion. This paper quantifies whether the presence of microplastics in sediments affects the development of small-scale soil surface roughness (SSR) properties during wind erosion, and whether there are any relationships between indices of SSR and microplastic flux due to wind erosion. Two contrasting substrates (well-sorted sand and poorly sorted soil) and two types of microplastic (polyethylene beads and polyester fibres) are used. SSR is quantified using geostatistically derived indicators calculated from high-resolution laser scans of the soil surface with and without microplastics, and before and after wind erosion simulated using a wind tunnel. Our results reveal the relative size of the microplastic to the mineral sediment is key to controlling microplastic flux.This article is part of the Theo Murphy meeting issue 'Sedimentology of plastics: state of the art and future directions'.

Microplastics are abundant in marine and terrestrial habitats, with rivers transporting particles to the sea. The River Thames catchment, UK, encompasses 15 million residents and many pollution sources. Temporal trends in microplastic abundance are sparse, with ad hoc studies in the estuary demonstrating great variability in concentrations. Taking a seasonal approach to time-series data collection, sediment and biota were sampled every three months over 2 yr. To account for the heterogeneity of microplastics in sediment, three grab samples were collected per survey. On average, 1000 ± 1100 (s.d.) plastic items kg^-1 were recovered from sediment, with significantly more from samples in July (summer) and September (autumn) 2020. The recorded concentrations were comparable with studies worldwide. Biota in the estuary are exposed to this plastic. Fish (Osmerus eperlanus, Platichthys flesus, Solea solea) and shrimp (Crangon crangon) contained on average 1.59 ± 2.62 items per individuals and 0.39 ± 0.95 items per individual, respectively. The greatest proportion of contaminated individuals was in December 2018 (winter; 75%) followed by March and June 2019 (spring; 42% and summer; 43%, respectively). Seasonal factors, such as rainfall, can affect plastic accumulation in an estuarine system, but these microplastics are not always bioavailable. Understanding the drivers of this variability is key in designing mitigation strategies and managing risk.This article is part of the Theo Murphy meeting issue 'Sedimentology of plastics: state of the art and future directions'.

Submarine canyons are recognized as accumulation areas for litter and conduits for deep-sea transport. Through the analysis of seafloor videos, we assess litter distribution in canyons of southern Italy, characterized by differences in morphology, connection to sediment sources and anthropogenic pressures. Litter was detected in all canyons, with highly variable concentration ranging from 0.1 to more than 100 items/100 m and a dominance of plastic, indicating a terrestrial or coastal origin for most of the litter. The lowest densities were from Cuma Canyon, incising the continental shelf edge at some distance from the coast and thus detached from major terrestrial inputs, while the highest were reported from the Messina Strait, where rivers draining highly populated areas debouche directly into offshore canyon heads. Canyon head proximity to rivers and densely populated coasts appears to be the main driver of litter abundance, although the uneven distribution between canyons reflects more closely the effect of geomorphological features, sediment transport and oceanographic processes, responsible for different abundances along the canyons' thalweg. Oceanographic processes and sediment transport can be involved in downcanyon litter transport; the latter is dominant in the case of gravity flows, which may deliver debris to the lowest canyon reaches, so far largely unexplored.This article is part of the Theo Murphy meeting issue 'Sedimentology of plastics: state of the art and future directions'.

Average microplastic (MP) abundances in each of 15 stormwater ponds in London, Canada ranged from 0.7 ± 0.7 particles per gram of dry weight sediment (g^-1 dw) to greater than 2323 ± 4643 g^-1 dw. Omitting one wetland cell and one hybrid pond produced a significantly higher median MP abundance for forebay versus main basin samples (p = 0.0058), and inlets produced greater mean abundances than outlets and open areas (20 ± 49, 10 ± 17, 4 ± 4 g^-1 dw, respectively). Considering all 15 ponds, the industrial/commercial and construction ponds produced higher means (684 ± 2387 g^-1 dw; 19 ± 22 g^-1 dw) than residential and open counterparts (6 ± 10 g^-1 dw; 6 ± 11 g^-1 dw). Fragments were the most common particle type in all but one pond, and fibre concentrations relative to other particle types were greatest in residential ponds. Copious styrene butadiene rubber (SBR) particles in an industrial pond are considered tyre wear due to proximity to manufacturers' parking areas and loading docks, and an automotive technology training school. Paint/coating chips accounted for 25% of the fragments analysed. With greater MP abundances than in sediment from tributaries, lakes and beaches of the same watershed, stormwater ponds prove to be exceptional transient sinks for MP debris.This article is part of the Theo Murphy meeting issue 'Sedimentology of plastics: state of the art and future directions'.

Microplastics (less than 5 mm diameter) are significant environmental contaminants whose small sizes and low densities facilitate transport by wind. Transport by wind erosion alongside soils or sediments results in mechanical abrasion of the plastic surfaces which can alter their physical and chemical properties. This paper uses laboratory simulations to determine the effects of up to 216 h of aeolian abrasion on polyethylene microplastics by angular, sub-rounded and rounded mineral sediments. During the abrasion process the mineral particles break down producing small fragments which adhere to the microplastic surfaces altering their surface roughness and chemistry. With increasing duration of abrasion the microplastic surface becomes coated with mineral fragments changing the dominant surface element from carbon to oxygen and silicon reflecting the composition of the erodents. The coating develops more rapidly when microplastics are abraded with angular sediments as these produce a lot of small fragments within the first 1-2 h. However, after more than 200 h of abrasion all the erodents had similar effects. A conceptual model of microplastic surface change is presented in which the plastic cracks and fractures, then flattens along with increasing density of sediment fragment cover. Surface changes may affect the ability of the plastics to transport airborne contaminants.This article is part of the Theo Murphy meeting issue 'Sedimentology of plastics: state of the art and future directions'.