Plastic island: A glance at microplastics enrichment in the nebkhas

Microplastics (MPs) are extensively detected in terrestrial environment, yet their occurrence in nebkhas, a widely distributed aeolian landform in arid and semi-arid regions, remains poorly understood. Based on field campaign, we quantified MPs distribution across three typical transects of farmland-downwind nebkha, highway-downwind nebkha, and contiguous nebkha in the agro-pastoral ecotone of northern China. The results revealed that MPs are significantly enriched in nebkhas compared to interdune, with enrichment ratios ranging from 1.45 to 2.89. MPs abundance generally decreased with increasing downwind distances along prevailing wind direction, but the changes in MPs particle size were independent of downwind distances. We proposed a hypotheses of a cascading three-stage process for explaining MPs enrichment in nebkhas, which refers firstly aeolian capturing, then morphological filtering, and finally biogeochemical stabilizing. PLI values were higher in nebkhas (1.73-5.00, PLI_zone = 2.78) than in interdunes (1.00-3.00, PLI_zone = 2.00), MPs enriched nebkhas can change from MPs-sinks to potential MPs-sources under environmental perturbations, causing soil structural degradation, vegetation impairment, and microbial dysfunction. Future research should focus on how MPs enrichment scales with nebkha morphology, successional stage, and topographic position to improve terrestrial MPs fate modelling.