Century-scale evolution of heavy metal speciation and content in Lake Chaohu sediments driven by human activities

Over the past century, human activities have intensified heavy metal pollution in lake sediments through various pathways, threatening lake ecosystem health. To formulate effective remediation strategies, it is essential to clarify the sources, concentrations, and speciation of these heavy metals. This study analyzed the concentrations, speciation characteristics, and sources of heavy metals (Cr, Ni, Cu, As, Cd, Pb) across different time periods, based on chronological stratification of sediment cores collected from 22 sampling sites in Lake Chaohu. The results revealed that heavy metal concentrations exhibited a phased increasing trend, with significantly higher levels in the western lake region compared to the eastern region; post-1990, the increase in the west was particularly pronounced. Speciation analysis indicated that Cr, Ni, Cu, As, and Pb were predominantly present in the residual fraction, while Cd was mainly in the acid-soluble fraction, indicating higher bioavailability. Source apportionment using Principal Component Analysis (PCA) and Positive Matrix Factorization (PMF) models demonstrated that natural sources dominated from the 1900s to the 1950s; agricultural sources increased to 41.66 % during the 1950s–1990s; and industrial and traffic sources became the primary anthropogenic contributors post-1990. The average annual growth rate of the Human Activity Intensity (HAI) index increased from 0.09 during 1950–1990 to 0.12 after 1990. This shift indicates that industrialization, urbanization, and traffic development were key drivers exacerbating heavy metal pollution, particularly leading to significant accumulation of reducible and oxidizable heavy metal fractions in the western lake region. • The HMs in Chaohu Lake showed a phased upward trend, and the enrichment degree in the western lake area was significantly higher than that in the eastern lake area. • Since the 1990s, the intensity of human activities has increased rapidly, which has significantly affected the content, source and occurrence of heavy metals. • It is recommended to adopt a sub-regional governance strategy and implement precise control measures for heavy metals from different sources.