Downward migrating microplastics in lake sediments are a tricky indicator for the onset of the Anthropocene.

Plastics are a recent particulate material in Earth's history. Because of plastics persistence and wide-range presence, it has a great potential of being a global age marker and correlation tool between sedimentary profiles. In this research, we query whether microplastics can be considered among the array of proxies to delimit the Anthropocene Epoch (starting from the year 1950 and above). We present a study of microplastics deposition history inferred from sediment profiles of lakes in northeastern Europe. The sediments were dated with independent proxies from the present back to the first half of the 18th century. Regardless of the sediment layer age, microplastic particles were found throughout the cores in all sites. Depending on particles' aspect ratio, less elongated particles were found deeper, while more elongated particles and fibers have reduced mobility. We conclude that interpretation of microplastics distribution in the studied sediment profiles is ambiguous and does not strictly indicate the beginning of the Anthropocene Epoch.

Dataset on microplastic concentrations, characteristics, and chemical composition in the marine surface waters of Latvia - the Eastern Gotland basin and the Gulf of Riga.

The dataset provides information on spectroscopically verified microplastics, both particles and fibers, from 44 marine surface water samples of two Baltic Sea sub-basins - the semi-enclosed Gulf of Riga and the Eastern Gotland Basin. Sampling was performed by using Manta trawl with a mesh size of 300 µm. Thereafter, the organic material was digested with sodium hydroxide, hydrogen peroxide and enzymes. Samples were filtered on glass fiber filters and analyzed visually, registering the shape, size, and color of each item. Where feasible, the polymer type was determined using Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy method. The number of plastic particles per m3 of filtered water was determined. The data presented in this article may be useful for further research on microplastic pollution, meta-analysis and calculation of microplastic flow. Interpretation and analysis of total acquired data on micro debris and microplastics are reported in the article "Occurrence and spatial distribution of microplastics in the surface waters of the Baltic Sea and the Gulf of Riga".

Seasonal dynamic of diazotrophic activity and environmental variables affecting it in the Gulf of Riga, Baltic Sea.

The semi-enclosed Baltic Sea experiences regular summer blooms of diazotrophic cyanobacteria. Previously, it has been conclusively demonstrated that in open nitrogen-limited parts of the Baltic Sea, cyanobacteria successfully fix atmospheric N2. At the same time, diazotrophic activity is still poorly understood in Baltic Sea sub-regions where nitrogen and phosphorus are co-limiting primary production. To address this gap in research, we used the15 N tracer method for in situ incubations and measured the N2-fixation rate of heterocyst-forming cyanobacteria and picocyanobacteria in the Gulf of Riga, Baltic Sea, from April to September. Physicochemical variables and phytoplankton community composition were also determined. Our results show that the dominant species of cyanobacteria for this region (Aphanizomenon flosaquae) was present in the phytoplankton community during most of the study period. We also establish that the N2-fixation rate has a strong correlation with the proportion of A. flosaquae biomass containing heterocysts (r = 0.80). Our findings highlight the importance of a heterocyst-focused approach for an accurate diazotrophic activity evaluation that is one of the foundations for future management and protection of the Baltic Sea.

Hide-and-seek: Threshold values and contribution towards better understanding of recovery rate in microplastic research.

Microplastic pollution has become one of the most pressing environmental issues. A fundamental criterion for risk assessment is the concentration of found microplastic that can be altered during microplastic isolating from the sample. Recovery rate (i.e. positive control) is an important feedback component that identifies accuracy, quality and efficiency of sample processing, same as physical and chemical impact. Here, using 100 µm red polystyrene (PS) beads we have tested some methodological steps that can be responsible for the possible microplastic losses during sample treatment and based on that, we provided a recovery rate threshold values. Our results support that the choice of the extraction method (vacuum filtration versus wet sieving) results in lower recoverability when vacuum filtration is used and that used separatory funnels size versus material amount impacts the efficiency or recoverability in density separation. We have also analysed microplastic recovery rate when different samples treatment steps from widely used isolation protocols (sediment and water) were applied and our results suggest that there are a number of factors affecting recovery rates, of which physical effects (loss by consecutive treatment steps due to material transfer) are more important than possible chemical degradation.•Sample filtration method determines recovery rate from < 40 to > 80%.•The number of sample processing steps involving transfer has a direct impact on recovery rate.•As a measure of quality assurance, recovery rate thresholds are introduced.

Occurrence and spatial distribution of microplastics in the surface waters of the Baltic Sea and the Gulf of Riga.

The study is comparing microplastic debris distribution and composition in the Gulf of Riga and the Eastern Gotland Basin, Baltic Sea. Samples from 44 stations were collected from coastal and open water sites using Manta trawl (mesh size 300 µm). The natural organic material was digested sequentially with sodium hydroxide, hydrogen peroxide and enzymes. Thereafter, micro-debris (16,315 particles) was identified by visual analysis and 5285 particles were analyzed with Attenuated Total Reflection Fourier Transform Infrared spectroscopy method. The abundance of particles varied from 0.09 to 4.43 particles per m-3. The fibers accounted for 66.1% of all encountered particles while the fragments for 30.2%. The predominant polymer types were polyethylene (77.9%) and polypropylene (11.1%). The relative proportion among polymer types varied considerably from station to station. The encountered concentrations of micro-debris were well in range of values reported from other regions of the Baltic Sea.

Development of fish age normalization technique for pollution assessment of marine ecosystem, based on concentrations of mercury, copper, and zinc in dorsal muscles of fish.

Correlation between metal concentrations in fish tissues and fish body size poses certain challenge when comparing concentration levels encountered at different locations or time periods by degrading performance of statistical tests due to variable age composition of fish sample pool. In order to overcome this, the concentrations of Hg, Cu, and Zn, measured in tissues of five fish species, were normalized to selected age group. Computed species-specific equations, based on empirically obtained exponential relationship, provided accurate estimates of the normalized concentrations under the conditions of substantial metal and fish age covariation. Obtained normalized and measured concentrations were then compared among sampling stations by means of commonly used analysis of variance (ANOVA) in combination with Tuckey's HSD test, where 11 out of 18 considered cases showed significant smoothing of the observed differences. The applied method worked well in the case of locally distributed coastal species populations where transformed data allowed clearer separation of spatial areas exhibiting different levels of pollution. At the same time, application of the method on pelagic fish species was less successful due to high mobility of specimens and mixed impact on the population originating from variable pollution levels at different areas of the entire migration region; therefore, attribution of a sample pool to a specific catchment area can cause a bias in assessment results.