Influence of suspended sediment front on nutrients and phytoplankton dynamics off the Changjiang Estuary: A FVCOM-ERSEM coupled model experiment

High-turbidity water is a common feature in the estuary and inner shelf. Sediment suspension functions as a modulator that directly influences the interactions among nutrients, phytoplankton and other related ecosystem variables. A physical-biological coupling model system was applied to examine the impact of sediment front on interactions among on suspended sediment, vertical mixing, nutrients and phytoplankton over the inner shelf off the high-turbidity, phosphate-limited Changjiang Estuary. The physical model was the Finite-Volume Community Ocean Model (FVCOM) and the biological model was the European Regional Seas Ecosystem Model (ERSEM). Results revealed that in the nearshore region the growth of phytoplankton over the spring-summer seasons was limited by suspended sediments and intensified vertical mixing during the autumn-winter seasons extended the sediment-induced suppression extended offshore to restrict the phytoplankton growth over the shelf. Nutrients were diluted by spreading of freshwater discharge and significantly decreased off the suspended sediment front due to the depletion by the offshore phytoplankton growth. The simulation results showed that although the diatom phytoplankton dominated the Chlorophyll alpha (Chl-alpha) concentration, the non-diatom group had a more contribution to the biomass. The relatively high phytoplankton biomass was found over the offshore deep underwater valley area as results of remote advection by the Taiwan Warm Current and weak turbulent mixing.