Seasonal difference in the behavior of polycyclic aromatic hydrocarbons in a large river-dominated estuary: Significance of winter sediment resuspension.

Marine sediments are an important sink for global polycyclic aromatic hydrocarbons (PAHs); however, the influence of seasonal hydrodynamic conditions on sedimentary PAHs along the continuum of large river-estuary-shelf systems remains unclear. Surface sediment samples collected from the Yangtze River Estuary (YRE) in winter (March 2015) and summer (July 2019) were analyzed for the sixteen USEPA priority PAHs (16 PAHs). The total concentration of 16 PAHs was substantially lower in winter (13.3-318.9 ng g, mean 74.2 ± 75.6 ng g) compared to summer (71.9-421.0 ng g, mean 168.9 ± 86.0 ng g). PAHs concentrations displayed a "low-high-low" trend along the river-estuary-shelf system, indicating a similar spatial distribution pattern between two seasons. Source analysis demonstrated that PAHs in the YRE were derived from a mixture of petrogenic and pyrolytic sources, with no distinct seasonal difference. Under the influence of East Asian Monsoon, riverine input PAHs were stored in nearshore estuary during summer, while winter sediment resuspension led to their outward transport. A lower reduction of PAHs in the estuarine mixing zone than that in the river channel and the continental shelf was observed in winter due to the sediment resuspension. This supports the notion that winter East Asian Monsoon-driven sediment resuspension significantly influences the behavior of sedimentary PAHs in the YRE.