Impacts of consecutive typhoons (Maysak and Haishen in 2020) on the benthic processes of a mega-tidal flat in highly developed area.

The relationship between sediment transport and the chlorophyll-a (Chl-a) distribution was investigated in a mega-tidal flat during two consecutive typhoons, Maysak and Haishen in 2020. In-situ measurements of the current velocity, suspended sediment concentration (SSC), and Chl-a were conducted at the upper (M1) and lower (M2) parts of the tidal flat in Muui Island from September 1 to 23, 2020. The current velocity and SSC (M1: 614 mg L-1; M2: 434 mg L-1) increased one day after the peak wind stress due to the tidal direction around Muui Island. At M1, the SSC increase was attributed to sediment resuspension, whereas it was likely driven by sediment advection at M2. Low Chl-a level during the typhoons was caused by reduced solar radiation and continuous high SSC. After the typhoons, the Chl-a concentrations increased, suggesting that typhoon-induced offshore vertical mixing eventually influenced the nearshore tidal flat, developing favorable conditions for Chl-a blooms.