Human Activity Drives Spatial Variability and Ecological Risks of Microplastics in Protected Wetlands of the Sanjiang Plain

ABSTRACT Microplastics (MPs) pollution is a pervasive global threat, yet its presence in protected freshwater wetlands remains poorly studied compared to urban and marine environments. In this study, we quantified MPs abundance, characteristics (shape, size, color), polymer composition, and evaluated ecological risk in surface waters of three national nature reserves on the Sanjiang Plain in northeast China. MPs concentrations were highest in Xingkaihu (XKH, 15.22 ± 7.13 particles/L), intermediate in Qixinghe (QXH, 7.4 ± 2.6 particles/L), and lowest in Honghe (HH, 3.1 ± 1.2 particles/L). Fibers, fragments, and films were the predominant particle types, and over 80% of MPs were smaller than 500 μm. White MPs (~27%) were the most common by color. Polymer analysis showed polypropylene (PP, 32%) and polyethylene (PE, 25%) as the dominant types, followed by polyethylene terephthalate (PET). Risk indices showed clear differences: HH had a low overall risk level, while XKH and QXH presented higher potential ecological hazards. To identify MPs' pollution sources across the reserves, we used the Microplastic Diversity Integrated Index to reflect the heterogeneity of pollution inputs. In combination with spatial data on human‐related Points of Interest, this approach identified two primary MPs emission sources. Agricultural activities were the dominant contributors in QXH and HH, while tourism‐related POI were the major source in XKH. Notably, clear signs of anthropogenic MPs input were evident even in remote wetland habitats, underscoring the far‐reaching impact of human activities. Our findings underscore the value of integrating human footprint information into freshwater MPs risk assessments and can inform spatially targeted pollution mitigation efforts in wetland ecosystems.