Analysis of microplastic sources in Wuliangsuhai Lake, China: Implications to microplastic deposition in cold, arid region lakes

Atmospheric transport and deposition represent an important pathway for terrestrial pollutants to enter aquatic environments. However, for many surface water environments such as lakes, rivers, and reservoirs, the contribution of MPs through atmospheric deposition is unclear, partly because the methods and technologies available for particle tracing have not been adequately developed. Herein, a multi-component approach was utilized to investigate atmospheric MP sources, inputs, and depositional characteristics to Wuliangsuhai Lake located within a cold and arid climatic region. The methods that were utilized include field monitoring experiments, HYSPLIT backward trajectory modeling, bivariable polar coordinate modeling, orthogonal matrix decomposition modeling (PMF), and dry settlement numerical modeling. These methods were combined with an assessment of particle morphology and composition. The results show that the atmospheric depositional flux of MPs to Wuliangsuhai Lake varied seasonally, with spring > summer > autumn. The deposited MPs were dominated by fibers. Polyethylene terephthalate (PET) and polyethylene (PE) were the most common polymer types. Microplastic sources also varied seasonally, although fibrous MPs were consistently derived mainly from small towns or cities. The PMF model defined four MP sources, including living, transportation, agricultural, and building sources. Sedimentation modeling showed that the dry atmospheric deposition of MPs in spring, summer, and autumn within the lake was 6.75 t, 5.34 t, and 3.88 t, respectively. This study shows that atmospheric deposition importantly contributes to MPs in cold areas lakes, and wind speed and direction are among the key factors influencing the amount, sources, and morphotype of atmospheric MPs deposited in lakes.