The Retention and Transport Patterns of Pollutants in the Radial Sand Ridges of the South Yellow Sea

The transport and dilution processes of pollutants are complex due to complicated morphology and dynamic factors in the radial sand ridges. The "moving stationary tidal wave" formed by progressive tidal wave from the East China Sea and the anti-clockwise rotary tidal wave from the Yellow Sea, together with the multiple radial tidal channels and flats, make the patterns different for exchange and retention of pollutants. Two retention timescales, the residence time and exposure time, were employed as diagnostic tools to the radial sand ridges, and surface wind was shown to be a significant factor to affect the transport patterns. Meanwhile, Lagrangian particles denoting pollutants were introduced for analyzing their transport trajectories and obtaining the retention timescales. Additionally, the finite-time Lyapunov exponents (FTLE) fields were integrated to locate Lagrangian coherent structures (LCSs). As time evolved, in most of the snapshots obvious longshore LCSs were detected at Xiyang, which is one of the deepest tidal channels and is demonstrated to be an important pathway of mass transport. Furthermore, the tidal channels were shown to have effects on confining the movements of water parcels or pollutants.