Abstract: To investigate the spatiotemporal distribution characteristics and influencing factors of microplastics in freshwater wetland systems, water and sediment sampling were conducted at 10 locations within the Huixian wetland basin, a representative Karst wetland, during both wet and dry seasons. The findings revealed that the abundance of microplastics in the Huixian wetland ranged from 5 466.7 to 24 333.3 n·m^-3(water) and 3 380.0 to 14 533.3 n·kg^-1(sediment) during the wet season. In the dry season, the range was 12 713.3 to 34 906.7 n·m^-3(water) and 11 866.7 to 42 486.7 n·kg^-1(sediment). Significant spatial and temporal differences were observed in the distribution characteristics of microplastics abundance (P<0.05). The dominant shapes of microplastics in the Huixian wetland were fibers, films, fragments, and pellets. Fibers were primarily found in water, while fragments were more prevalent in sediments. Microplastics with small particle sizes (0.45 μm to 0.5 mm) were predominant in both water and sediments during both wet and dry seasons. The abundance of microplastics decreased with the increasing of particle size. The identified polymer components were mainly polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP), and polyethylene (PE). PE was the predominant polymer type in water, while PET dominated in sediments. The abundance of microplastics in the wet season was significantly lower than that in the dry season, likely attributed to the dilution effect caused by rising water levels. Moreover, the dry season exhibited higher proportions of microplastics with small particle sizes (0.45 μm to 0.5 mm) and a higher proportion of PE among the polymer types. In terms of spatial distribution, areas such as tourist sites, concentrated fishery and agricultural zones, and vicinity of villages displayed higher microplastics abundance compared to other areas. The main sources of microplastics in the Huixian wetland include rural domestic sewage discharge, fish farming, agricultural activities, and tourism.

Key words: Huixian wetland, surface water, sediment, microplastics, temporal and spatial distribution, influencing factor