Occurrence and distribution of microplastics in marine sediments along the Belgian coast

Plastic debris is known to undergo fragmentation at sea, which leads to the formation of microscopic particles of plastic; the so called ‘microplastics’. Due to their buoyant and persistent properties, these microplastics have the potential to become widely dispersed in the marine environment through hydrodynamic processes and ocean currents. In this study, the occurrence and distribution of microplastics was investigated in Belgian marine sediments from different locations (coastal harbours, beaches and sublittoral areas).Particles were found in large numbers in all samples, showing the wide distribution of microplastics in Belgian coastal waters. The highest concentrations were found in the harbours where total microplastic concentrations of up to 390 particles kg⁻¹ dry sediment were observed, which is 15-50 times higher than reported maximum concentrations of other, similar study areas.The depth profile of sediment cores suggested that microplastic concentrations on the beaches reflect the global plastic production increase.     

Habitat associations of floating debris and marine birds in the North East Pacific Ocean at coarse and meso spatial scales

While many surface foraging seabirds ingest plastic, the spatial overlap of these far-ranging predators with debris aggregations at-sea is poorly understood. We surveyed concurrent distributions of marine birds and debris along a 4400 km cruise track within a debris accumulation area in the North East Pacific Ocean using line and strip transect methods. Analysis of debris and bird distributions revealed associations with oceanographic and weather variables at two spatial scales: daily surveys and hourly transects. Hourly bird abundance (densities; 0-9 birds km⁻²) was higher in lower wind and shallower water. Hourly debris abundance (densities; 0-15,222 pieces km⁻²) was higher in lower wind, higher sea-level atmospheric pressure and deeper water. These results suggest that debris and seabird abundance and community structure are influenced by similar environmental processes, but in opposing ways, with only three far-ranging seabird species (Black-footed Albatross, Cook’s Petrel and Red-tailed Tropicbird) overlapping with high debris concentrations over meso-scales.     

Microplastics as contaminants in the marine environment: a review

Since the mass production of plastics began in the 1940s, microplastic contamination of the marine environment has been a growing problem. Here, a review of the literature has been conducted with the following objectives: (1) to summarise the properties, nomenclature and sources of microplastics; (2) to discuss the routes by which microplastics enter the marine environment; (3) to evaluate the methods by which microplastics are detected in the marine environment; (4) to assess spatial and temporal trends of microplastic abundance; and (5) to discuss the environmental impact of microplastics. Microplastics are both abundant and widespread within the marine environment, found in their highest concentrations along coastlines and within mid-ocean gyres. Ingestion of microplastics has been demonstrated in a range of marine organisms, a process which may facilitate the transfer of chemical additives or hydrophobic waterborne pollutants to biota. We conclude by highlighting key future research areas for scientists and policymakers.     

Physical and chemical effects of ingested plastic debris on short-tailed shearwaters, Puffinus tenuirostris, in the North Pacific Ocean

We investigated the plastics ingested by short-tailed shearwaters, Puffinus tenuirostris, that were accidentally caught during experimental fishing in the North Pacific Ocean in 2003 and 2005. The mean mass of plastics found in the stomach was 0.23 g per bird (n = 99). Plastic mass did not correlate with body weight. Total PCB (sum of 24 congeners) concentrations in the abdominal adipose tissue of 12 birds ranged from 45 to 529 ng/g-lipid. Although total PCBs or higher-chlorinated congeners, the mass of ingested plastic correlated positively with concentrations of lower-chlorinated congeners. The effects of toxic chemicals present in plastic debris on bird physiology should be investigated.     

Properties of natural supraglacial debris in relation to modelling sub‐debris ice ablation

As debris‐covered glaciers become a more prominent feature of a shrinking mountain cryosphere, there is increasing need to successfully model the surface energy and mass balance of debris‐covered glaciers, yet measurements of the processes operating in natural supraglacial debris covers are sparse. We report measurements of vertical temperature profiles in debris on the Ngozumpa glacier in Nepal, that show: (i) conductive processes dominate during the ablation season in matrix‐supported diamict; (ii) ventilation may be possible in coarse surface layers; (iii) phase changes associated with seasonal change have a marked effect on the effective thermal diffusivity of the debris. Effective thermal conductivity determined from vertical temperature profiles in the debris is generally ~30% higher in summer than in winter, but values depend on the volume and phase of water in the debris. Surface albedo can vary widely over small spatial scales, as does the debris thickness. Measurements indicate that debris thickness is best represented as a probability density function with the peak debris thickness increasing down‐glacier. The findings from Ngozumpa glacier indicate that the probability distribution of debris thickness changes from positively skewed in the upper glacier towards a more normal distribution nearer the terminus. Although many of these effects remain to be quantified, our observations highlight aspects of spatial and temporal variability in supraglacial debris that may require consideration in annual or multi‐annual distributed modelling of debris‐covered glacier surface energy and mass balance. Copyright © 2012 John Wiley & Sons, Ltd.     

Modelling a cohesive‐frictional debris flow: an experimental,theoretical, and field‐based study

The rheology of debris flows is difficult to characterize owing to the varied composition and to the uneven distribution of the components that may range from clay to large boulders, in addition to water. Few studies have addressed debris flow rheology from observational, experimental, and theoretical viewpoints in conjunction. We present a coupled rheological‐numerical model to characterize the debris flows in which cohesive and frictional materials are both present. As a first step, we consider small‐scale artificial debris flows in a flume with variable percentages of clay versus sand, and measure separately the rheological properties of sand–clay mixtures. A comparison with the predictions of a modified version of the numerical model BING shows a reasonable agreement between measurements and simulations. As application to a field case, we analyse a recent debris flow that occurred in Fjærland (Western Norway) for which much information is now available. The event was caused by a glacial lake outburst flood (GLOF) originating from the failure of a moraine ridge. In a previous contribution (Breien et al., Landslides, 2008 , 5: 271–280) we focused on the hydrological and geomorphological aspects. In particular we documented the marked erosion and reported the change in sediment transport during the event. In contrast to the laboratory debris flows, the presence of large boulders and the higher normal pressure inside the natural debris flow requires the introduction of a novel rheological model that distinguishes between mud‐to–clast supported material. We present simulations with a modified BING model with the new cohesive‐frictional rheology. To account for the severe erosion operated by the debris flow on the colluvial deposits of Fjærland, we also suggest a simple model for erosion and bulking along the slope path. Numerical simulations suggest that a self‐sustaining mechanism could partly explain the extreme growth of debris flows running on a soft terrain.     

The influence of organic debris on channel morphology and bedload transport in a New Zealand forest stream

The behaviour and form of, and bedload sediment transport through, a 3.5 m wide forest stream have been monitored for nearly three years. Bedload transport is highly episodic and spatially variable, and is controlled less by water discharge than by sediment availability. Organic debris in the channel creates temporary base levels and sites at which coarse sediment may remain stored for long periods; collapse or disruption of log and debris jams makes sediment available for transport in only a small proportion of the runoff events that are actually competent to move the material. Even then, sediment travels only a short distance before being redeposited, frequently behind debris accumulations further downstream. Rates of sediment transport during a given runoff event can vary markedly over short distances along the stream, again depending on whether sediment was made available for transport by log jam collapse upstream. Organic debris is therefore a major constraint on the application of physical laws and theories to explaining sediment movement in, and the morphology of, this stream.     

Bed material texture in low order streams on the Queen Charlotte Islands,British Columbia

Low order channels comprise a large proportion of the links of every drainage basin, and are often at the centre of land management concerns. They exhibit hydrological and geomorphological characteristics atypical of higher order links. This paper examines the nature and causes of variations in the bed material texture of two streams on the Queen Charlotte Islands, British Columbia. The extant, functional exponential model is found to be inadequate for explaining observed changes in grain size parameters with distance downstream. Recurrent disruption of sediment transport by large organic debris jams, and the sporadic contamination of the fluvial sediment population by colluvial inputs, preclude the development of longitudinal structure. Rather, grain size varies erratically over short distances. A stochastic model best describes the observed variations, and should be adopted as an alternative to the exponential model in low order links. Characteristic variances are controlled by the degree of hillslope-channel coupling, and the extent and characteristics of non-alluvial storage mechanisms.     

The Llullaillaco volcano, northwest Argentina: construction by Pleistocene volcanism and destruction by sector collapse

Llullaillaco is one of a chain of Quaternary stratovolcanoes that defines the present Andean Central Volcanic Zone (CVZ), and marks the border between Chile and Argentina/Bolivia. The current edifice is constructed from a series of thick dacitic lava flows, forming the second tallest active volcano in the world (6739 m). K–Ar and new biotite laser ⁴⁰Ar/³⁹Ar step-heating dates indicate that the volcano was constructed during the Pleistocene (≤1.5 Ma), with a youngest date of 0.048±0.012 Ma being recorded for a fresh dacite flow that descends the southern flank. Additional ⁴⁰Ar/³⁹Ar measurements for andesitic and dacitic lava flows from the surrounding volcanic terrain yield dates of between 11.94±0.13 Ma and 5.48±0.07 Ma, corresponding to an extended period of Miocene volcanism which defines much of the landscape in this region. Major- and trace-element compositions of lavas from Llullaillaco are typical of Miocene–Pleistocene volcanic rocks from the western margin of the CVZ, and are related to relatively shallow-dipping subduction of the Nazca plate beneath northern Chile and Argentina.Oversteepening of the edifice by stacking of thick, viscous, dacitic lava flows resulted in collapse of its southeastern flank to form a large volcanic debris avalanche. Biotite ⁴⁰Ar/³⁹Ar dating of lava blocks from the avalanche deposit indicate that collapse occurred at or after 0.15 Ma, and may have been triggered by extrusion of a dacitic flow similar to the one dated at 0.048±0.012 Ma. The avalanche deposits are exceptionally well preserved due to the arid climate, and prominent levées, longitudinal ridges, and megablocks up to 20-m diameter are observed.The avalanche descended 2.8 km vertically, and bifurcated around an older volcano, Cerro Rosado, before debouching onto the salt flats of Salina de Llullaillaco. The north and south limbs of the avalanche traveled 25 and 23 km, respectively, and together cover an area of approximately 165 km². Estimates of deposit volume are hampered by a lack of thickness information except at the edges, but it is likely to be between 1 and 2 km³. Equivalent coefficients of friction of 0.11 and 0.12, and excess travel distances of 20.5 and 18.5 km, are calculated for the north and south limbs, respectively. The avalanche ascended 400 m where it broke against the western flank of Cerro Rosado, and a minimum flow velocity of 90 m s⁻¹ can be calculated at this point; lower velocities of 45 m s⁻¹ are calculated where distal toes ascend 200 m slopes.It is suggested that the remaining precipitous edifice has a high probability for further avalanche collapse in the event of renewed volcanism.