Quantification of wind-driven MP mobilisation potential in semi-arid regions in Kazakhstan using wind tunnel experiments

The northeastern steppe landscape of Kazakhstan, with its loess soils, flat terrain, and erosive climate, is highly susceptible to aeolian processes, which can lead to extensive and variable soil mobilisation and deposition. Although agricultural activity has been low in recent decades, the introduction of modern practices has intensified agriculture, potentially leading to greater plastic emissions from irrigation and plant growth and protection systems. Despite extensive global research on microplastics (MP, <5 mm in size) in natural systems, their transport and deposition via aeolian processes, as well as their production and input rates on agricultural land in continental climate zones, have received little attention to date.

In this study, wind-driven MP mobilisation was quantified by on-farm experiments on two sites, with Zhelezinka on Haplic Kastanozem soil, and Shortandy on Haplic Chernozem soil. While both sites are for agricultural use, the management differs in terms of soil tillage, fertilizer input, pest management, and irrigation. A portable boundary layer wind tunnel was applied for five 15-minute tests with a wind speed of 14 m s⁻¹. This accounts for an average wind speed that occurs in this region for an average of six hours per year, representing relatively extreme conditions used to assess the overall potential for wind-driven MP mobilisation at the study sites. Samples were collected using an aluminium wedge trap, covering approximately 1% of the tunnel mouth's area, and were characterised using confocal micro-Raman spectroscopy.

The total results reveal 2.24 g min⁻¹ mobilised soil material at Shortandy and 14.52 g min⁻¹ at Zhelezinka, with MP mobilisation of 0.01 g min⁻¹ (89 MP items) and 0.14 g min⁻¹ (1206 MP items), respectively. The detected MP varied in shape (fragments and fibres) and size, with all detections having diameters smaller than 150 μm. Greater variability in MP types, predominantly fragments (PPSU, PP, PE, PMMA), was observed at Zhelezinka. In contrast, Shortandy showed fewer MP mobilisation, with only one plastic type (PA) identified and a more balanced distribution between fragments and fibres compared to Zhelezinka. The overall fragment-to-fibre ratio is 31:1. The differences in MP mobilisation between the sampling sites can be explained by varying land use durations and intensities. The study highlights that wind erosion can make a significant contribution to the local and regional distribution of MP in the northeastern steppe of Kazakhstan.