Iron-binding ligands in Dutch estuaries are not affected by UV induced photochemical degradation

This study shows that ultraviolet B (UV-B: 280–315 nm) and UV-A (315–400 nm) have no significant influence on the photodegradation of organic Fe(III)-binding ligands in estuarine waters from Marsdiep and Scheldt (The Netherlands). High salinity estuarine seawater from the Marsdiep and Scheldt contains concentrations of organic Fe(III)-binding ligands as high as 24.4 equivalent of nM Fe (eq nM Fe) and 4.6 eq nM Fe, respectively, with conditional stability constants (K′) of 1021.0 and 1020.1, respectively. Investigation of the relation between the organically bound iron fraction and the photoproduction of Fe(II) in the estuarine Marsdiep and Scheldt water shows that the concentration of Fe(II) produced was very low (< 240 pM). This demonstrates that the major part of the organically complexed Fe(III) is not involved in photoinduced Fe redox cycling. Consequently UV has no influence on the transport of dissolved organically complexed Fe(III) from the estuarine environment to the coastal zone.