Historical reconstruction of microplastic accumulation in shallow lake sediments and its anthropogenic drivers: A case study in Lake Liangzi

Microplastics (MPs) are persistent contaminants in freshwater systems, yet their long-term accumulation patterns and dominant drivers in inland lakes remain poorly constrained. Here, we reconstruct microplastic deposition over the past ~200 years using a sediment core from Lake Liangzi, located in the middle–lower reaches of the Yangtze River, China. A robust ²¹⁰Pb–¹³⁷Cs chronology was established for the upper 66 cm of the core (ca. 1823–2019). Microplastics were extracted at 1 cm resolution, and their abundance, size, shape, and colour were quantified by optical microscopy, with polymer composition identified using micro-Fourier transform infrared spectroscopy (μ-FTIR). The results show a pronounced increase in MP abundance through time, with clear phase shifts. CONISS cluster analysis distinguishes three stages: a low-background period prior to 1957, a phase of moderate increase between 1958 and 1984, and a period of rapid accumulation since 1984. Microplastic abundance is positively correlated with total organic carbon (TOC) and total nitrogen (TN), indicating close coupling with sedimentary organic matter enrichment. Redundancy analysis demonstrates that anthropogenic factors, particularly plastic production, population growth, fisheries activity, economic development, and land-use change, explain most of the variance in MP accumulation, whereas climatic variables play a comparatively minor role. Analysis of land-use change between 1980 and 2020 reveals expanding built-up areas and declining cropland, consistent with intensified urbanization and increased microplastic inputs. Together, these results provide clear sedimentary evidence that human activities are the dominant drivers of long-term microplastic accumulation in inland lake sediments, highlighting the growing legacy of plastic pollution in freshwater ecosystems.