Dissolved iron distribution and organic complexation in the coastal waters of the East China Sea

Higher surface Lt concentrations were observed during the spring. The average surface Lt concentrations of estuary stations in spring and autumn were 40.0 ± 26.8 and 23.2 ± 7.8 nmol/L, respectively. The concentration of D-Fe and Lt in the bottom water was higher than that observed in surface water and exhibited less seasonal variability. Strong ligands were observed in spring estuary surface water. The average surface logK'FeL values in spring and autumn were 12.9 ± 0.8 and 11.7 ± 0.5, respectively. The total ligand concentration in this study was generally in excess of the dissolved iron, particularly in autumn at offshore stations. Higher excess organic ligand concentrations were also generally observed in the upper water column compared to bottom waters in autumn.