Holostic microplastics assesment in small urban lake (Velnezers, Latvia)

Description

The data explores the presence, seasonal variations, historical accumulation and deposition rates of microplastics (MPs) in an urban lake within the Baltic region of Northern Europe. The dataset includes detailed information on MP concentrations in surface water, sedimentation rates, and the distribution of MPs within lake sediments. Key findings from the dataset include: Surface water MP concentrations were highest in summer (5.71 particles/m³) and decreased during winter (0.75 particles/m³), indicating seasonal variations; The MP deposition rate was calculated at 9.47 particles/cm²/year (or 4.31 μg/cm²/year); The sediment core analysis revealed MPs in layers older than 1950, predating the mass production of plastics; The predominant polymer types were polyethylene, polystyrene, and polypropylene, with fibres being more abundant in surface water and fragments in sediment layers. The data provides a comprehensive snapshot of MPs in an urban lake, from seasonal fluctuations in surface water to long-term deposition patterns in sediment cores. Researchers can use this dataset to explore the dynamics of MP pollution in freshwater ecosystems, the impact of urbanisation on MP concentrations, and the relationship between seasonal variation and MP presence. Additionally, the data can be used to refine monitoring methods for MPs, particularly in urban lakes, where rapid, cost-effective approaches are crucial for ongoing surveillance. The data was collected using well-established MP research methods: Manta trawling for surface water sampling to measure MP concentrations, sediment trapping to assess MP sedimentation rates over one year, sediment coring to examine MP distribution in dated sediment archives. MP particles were identified and characterised using Attenuated Total Reflection (ATR) and micro-Fourier Transform Infrared (FTIR) spectroscopy. Sediment core chronology was determined using 210Pb dating and the Bayesian Plum model, which revealed sediment layers corresponding to periods before large-scale plastic production. This dataset is valuable for researchers studying MP pollution in freshwater environments, particularly in urban settings. It can be used to establish baselines for future monitoring efforts and to develop more effective, resource-efficient methods for MP surveillance.

Steps to reproduce

Sampling was done in Lake Velnezers, urban lake in Latvia. Sampling: • Surface water: Seven surface water samples were collected between April 2019 and January 2020, approximately every six weeks. The samples were obtained by trawling a Manta net (Hydro-Bios, mesh size 300 μm, nylon material) from the stern of a boat for 20 minutes outside the wake zone. The filtered water volume was 24.23-29.33 m³, measured using a mechanical flow meter (Hydro-Bios). After trawling, the net was rinsed from outside to concentrate sample in the cod end, which was then transferred to a glass tray, covered with a metal lid, and stored at 2-4°C until further processing. • Sediment trap: Sediment samples were collected via sediment trap made from polyvinyl chloride (PVC) and stainless-steel. The trap was installed in February 2019 at the deepest part of the lake and left near the lakebed for six months to capture sedimentation during the spring and summer productive season. The trap was then emptied and redeployed in August 2019 and repeatedly retrieved in January 2020, providing samples from the autumn and winter stagnant season. • Sediment core: Sediment core samples were taken in February 2019 using a Kayak/HTH gravity corer equipped with a PVC sample tube (8.2 cm internal diameter). The core reached a total length of 32 cm and was sliced into 2 cm layers to increase sample resolution. These layers were subsampled for MP analysis and dating and stored in pre-cleaned glass trays covered with metal lids at 2-4°C until further processing. Samples treatment: MPs were isolated using a multi-step treatment protocol involving oxidation, surfactant extraction, enzymatic digestion (using cellulase, viscozyme in acetate buffer, and alcalase in TRIS buffer), and density separation with sodium polytungstate solution (density 1.9 g/cm³). MPs in surface water samples were filtered through glass fibre filters (1.2 μm pore size), while MPs in sediment trap and core samples were vacuum filtered through silver membrane filters (5 μm pore size). Samples analysis: For surface water, MPs were counted under a Leica DM400 B LED light microscope, and visual identification was aided by Leica Application Suite V4.1 software. Particle colour, dimensions (length and width) and shapes (fibre or fragment) were measured. For polymer identification, ATR-FTIR spectroscopy (Thermo Scientific Nicolet iS20, OMNIC software >15000 spectra) was used. Sediment MPs were analysed using a μFTIR spectrometer (Agilent Cary 670/620) fitted with a focal plane array detector in reflection mode. SiMPle software was used to automatically identify and quantify MPs, estimate mass. Additionally, the aspect ratio (AR) of particles was calculated to determine their shape, categorising them as fibres (AR ≤ 0.11) or fragments (AR > 0.11). For smaller particles (<500 μm), AR was also classified into four categories to analyse their distribution in the sediment profile.

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