The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

The maximum turbidity zone (MTZ) in the estuary has a trapping effect on organic pollutants, thereby affecting their river-sea transport. This study investigated the variations and particle size distribution of dissolved and particulate polycyclic aromatic hydrocarbons (PAHs) over a complete tidal cycle, and studied the effects of suspended particulate matter (SPM), salinity, organic carbon (OC) and elemental carbon (EC) on the water-SPM partition coefficients (K_d) of PAHs in the Jiulong River MTZ, Fujian Province, China. The concentrations of particulate PAHs increased in bottom water during the flood tides and ebb tides because of the resuspension and water-SPM mixing caused by the fast water velocity. Phenanthrene (Phe), anthracene (Ant), benzo[a]anthracene (BaA) and chrysene (Chy) were mainly distributed on fine (<10 μm) particles, accounting for 38%-43% of the total amount. SPM concentrations and OC significantly (Spearman, p<0.05) affected Log K_d values of PAHs. However, there was no significant positive correlation between Log K_d and EC, indicating that the active adsorption pore sites of EC may be occupied by microorganisms and other organic pollutants in the MTZ. From the upstream to the downstream of the MTZ, the concentrations of dissolved PAHs decreased gradually, while in the central MTZ, particulate PAHs concentrations increased 43 times, suggesting that the trapping of organic pollutants by SPM reduced their transport fluxes into the ocean.
 

Elemental carbon,Jiulong River,particle size distribution,maximum turbidity zone,PAHs