Centennial-scale sediment record and source traceability of heavy metals in Laizhou Bay, Bohai Sea, China.

The accumulation of heavy metals in marine sediments poses a significant threat to marine ecosystems. This study utilized a ²¹⁰Pb-dated sediment core from Laizhou Bay to reconstruct historical sediment variability, trace heavy metal sources, and evaluate their contamination at a centennial timescale. By intergrating Self-Organizing Map, Principal Component Analysis and Positive Matrix Factorization, we conducted a comprehensive analysis of the sources of heavy metal pollution in Laizhou Bay. Our results revealed four distinct periods of heavy metal distribution into: 1906-1930, 1930-1976, 1976-2000, and 2000-2020, corresponding to shifts in human activities and changes in the Yellow River course over the past century. This study is the first to introduce the SOM algorithm into the field of heavy metal source analysis in Laizhou Bay, exhibiting better classification robustness for non-linearly coupled combinations like Co-Cr-Ni-V. By combined with PMF, we identified four primary sources of heavy metals: natural sources, mixed anthropogenic and natural sources, agricultural activities, and industrial production, with contribution rate of 28.37, 28.86, 14.03 and 28.74%, respectively. Notably, Cadmium (Cd) was identified as the most enriched pollutant, demonstrating pronounced anthropogenic amplification. These results provide valuable insights for targeted pollution mitigation strategies, emphasizing the need for source-specific management approaches in coastal zones under increasing anthropogenic pressure.