Here we provide the biological model equations (Text S1). In Text S2, model validation for IMAGE-GNM and ROMS are present by comparing with measured values (Figure. S2-S4). Finally, model limitation and improvements are discussed (Text S3).

Figures start with Figure S1 showing the scheme of the coupled physical–biological numerical model (ROMS) for the Taiwan Strait linking river N input from the IMAGE-GNM model. Figures S2-S4 show the model validations. Thereafter, we show the monthly precipitation and runoff in Figure S5, monthly observed river discharge and simulated total nitrogen export flux in Figure S6. Monthly simulated mean surface temperature was shown in Figure S7 and salinity in Figure S8. Then simulated surface mean surface nitrate, ammonium, Chla difference between with and without river nitrogen input are shown in Figures S9-S11, respectively. Finally, monthly mean values of key environmental factors controlling the phytoplankton growth rate were plotted in Figures S12-S14.

Table S1 show the Characteristics of the main rivers influencing the Taiwan Strait. Table S2 is a summary of estimated DIN flux by main sources to the TWS in 2001-2010. Table S3 list the correlation coefficient (r) and p value in the correlation analysis between the key environmental factor anomalies at annual scale.

Data tables S1-S3 are data supporting the conclusions.