Elena Esiukova

On some physical and dynamical properties of microplastic particles in marine environment

Simplified physical models and geometrical considerations reveal general physical and dynamical properties of microplastic particles (0.5-5mm) of different density, shape and size in marine environment. Windage of extremely light foamed particles, surface area and fouling rate of slightly positively buoyant microplastic spheres, films and fibres and settling velocities of negatively buoyant particles are analysed. For the Baltic Sea dimensions and under the considered idealised external conditions, (i) only one day is required for a foamed polystyrene particle to cross the sea (ca. 250km); (ii) polyethylene fibres should spend about 6-8months in the euphotic zone before sinking due to bio-fouling, whilst spherical particles can be retained on the surface up to 10-15years; (iii) for heavy microplastic particles, the time of settling through the water column in the central Gotland basin (ca. 250m) is less than 18h. Proper physical setting of the problem of microplastics transport and developing of physically-based parameterisations are seen as applications.

Microplastics in Baltic bottom sediments: Quantification procedures and first results

Microplastics in the marine environment are known as a global ecological problem but there are still no standardized analysis procedures for their quantification. The first breakthrough in this direction was the NOAA Laboratory Methods for quantifying synthetic particles in water and sediments, but fibers numbers have been found to be underestimated with this approach. We propose modifications for these methods that will allow us to analyze microplastics in bottom sediments, including small fibers. Addition of an internal standard to sediment samples and occasional empty runs are advised for analysis quality control. The microplastics extraction efficiency using the proposed modifications is 92±7%. Distribution of microplastics in bottom sediments of the Russian part of the Baltic Sea is presented. Microplastic particles were found in all of the samples with an average concentration of 34±10 items/kg DW and have the same order of magnitude as neighbor studies reported.

Plastic pollution on the Baltic beaches of Kaliningrad region, Russia

Contamination of sandy beaches of the Baltic Sea in Kaliningrad region is evaluated on the base of surveys carried out from June 2015 to January 2016. Quantity of macro/meso/microplastic objects in the upper 2cm of the sandy sediments of the wrack zone at 13 sampling sites all along the Russian coast is reported. Occurrence of paraffin and amber pieces at the same sites is pointed out. Special attention is paid to microplastics (range 0.5-5mm): its content ranges between 1.3 and 36.3 items per kg dry sediment. The prevailing found type is foamed plastic. No sound differences in contamination are discovered between beaches with high and low anthropogenic load. Mean level of contamination is of the same order of magnitude as has been reported by other authors for the Baltic Sea beaches.

Behavior of Microplastics in Coastal Zones

Abstract Physical and dynamic properties of marine microplastic (MP) particles are summarized, with relevance to their behavior in the coastal zone. The density range, size classes, and typical particle shapes are presented, and their variation with time due to weathering, biofouling, and mechanical degradation in the swash zone is considered. The dependence of the time rate of increase of integral particle density on the particle shape due to its biofouling shows that floating fibers and threads (“one-dimensional” (1-D) particles) are the first to begin sinking, followed by 2-D films and flakes, and then 3-D fragments. Mechanical fragmentation in the swash zone of plastic samples made of low-density polyethylene (LDPE), polystyrene (PS), polypropylene (PP), and foamed polystyrene (foamed PS) shows qualitative features of the generated MP particles and indicates that increase in mass of MPs with time is exponential. Dynamic behavior of MPs is discussed on the base of knowledge from classical hydrodynamics, marine sedimentology, and physical oceanography. Shape-dependent manner of the particle sinking and the value of the terminal settling velocity are characterized in terms of the particle size, density, and angularity. Critical velocity of resuspension by a unidirectional flow is addressed in terms of the Shields diagram, summarizing available published data on laboratory experiments on the particles with properties similar to those of MPs. Consideration of motion of particles in an oscillatory flow under surface waves and in roll structures illuminates mechanisms of mixing of MPs and natural marine debris. Analysis of the observed sorting of sediment grains under the influence of surface waves raises the question of probable sorting of MPs in the water column of the coastal zone, leading to different transport for different kinds of MP particles, including the offshore export of smaller MPs, onshore transport of larger particles, and possible effect of arresting of finer MPs under coarser sediment grains. Typical velocity scales of natural convective flows and upward/downward motions within the Langmuir circulation cells are shown to be of the same order of magnitude as the settling velocity of common MPs—units of centimeters per second—which suggests the importance of these mixing mechanisms for the motion of MP particles. As a natural case study, the events of washouts of heavily intermixed patches of seaweed, amber stones, and MPs onto the beaches of the Baltic Sea after severe storms are examined. It is concluded that stormy episodes seem to bring repeatedly larger plastics to the surf and swash zone and export smaller pieces offshore.

Spring thermocline formation in the coastal zone of the southeastern Baltic Sea based on field data in 2010–2013

The transition from winter vertical mixing to the formation of the spring thermocline in the southeastern Baltic Sea is studied based on data from the hydrophysical measurements program (11 expeditions) in the Russian part of Gdansk Bay in March–June 2010, 2011, and 2013. CTD measurements were taken along the standard 18-km transect across the isobaths with a 500-m step abeam the city of Baltiysk. A set of frequently measured data was collected in a 1–2 week interval from the end of March to the beginning of May, which made it possible to analyze the transformation of the vertical thermal structure of water from inverse winter type to the summer stratification with the transition of temperature over the temperature of the density maximum. Series of repeated measurements at the deep and coastal stations as well as surface and subsurface towed measurements were carried out. The fact that lenses of freshened warmer water appear at the surface almost simultaneously with intensification of cold intrusions in intermediate (10–40 m) layers makes it possible not only to confirm the advective nature of the formation of the spring thermocline in the Baltic Sea, but also to hypothesize about the intensification of intrabasin exchange when winter-time vertical mixing ceases: the potential energy excess supported by vertical mixing in the 60-m upper quasi-homogeneous layer (UQL) of the Baltic Proper, in which the horizontal estuarine salinity gradient is significant, is converted to kinetic energy of exchange currents as the mixing process terminates. Such water dynamics makes it possible to explain the intensification of intrusions in the Baltic in spring and the formation of the cold intermediate layer due to the fast propagation of late-winter UQL water from the Bornholm Basin to the Baltic Proper. The results agree well with earlier published studies of other authors.