Effects of organic carbon burial on biomarker component changes in contamination in northeast Dianchi watershed

The upper reaches of the Yangtze River have experienced increasing anthropogenic stress. Quantitative tracing of carbon (C) sources and ecological risks through biomarkers i.e., polycyclic aromatic hydrocarbons (PAHs) and n-alkanes is significant for C neutrality and sequestration. Here, source and sink patterns, and factors influencing C burial and biomarker components in a small catchment of Dianchi Lake were explored. The sediment core covered the period 1855-2019. Before 1945, the organic C accumulation rate (OCAR) ranged from 0.71 to 5.12 mg cm^-2 yr^-1, and the PAHs and n-alkanes fluxes were 106.99-616.09 ng cm^-2 yr^-1 and 5.56-31.37 μg cm^-2 yr^-1. During 1945-2005, the OCAR, PAH, and n-alkane burial rapidly increased from 3.19 to 16.17 mg cm^-2 yr^-1, 230.40 to 2538.81 ng cm^-2 yr^-1, and 11.63 to 61.90 μg cm^-2 yr^-1. During 1855-2019, deposition fluxes of PAHs and n-alkanes increased 13.01 and 9.14 times, resulting in increased C burial, driven by environmental changes. A PMF model and the diagnostic ratio indicated that PAHs from coal combustion and traffic emission increased from 22.32% to 65.20% during 1855-2019. The PAH concentrations reflected normal-moderate contamination and potential risks to the aquatic environment. The results facilitate a comprehensive understanding of anthropogenic-driven interactions between increasing OC burial and ecological risks.