Pathways contributing to the formation and decay of ferrous iron in sunlit natural waters

Pathways contributing to the formation and decay of Fe(II) in sunlit natural waters are investigated in this chapter with insights drawn from both laboratory experiments and kinetic modelling. Our results support previous findings that superoxide-mediated iron reduction (SMIR) is the main pathway for photochemical reduction of Fe(III) at pH 8 while light-induced ligand to metal charge transfer (LMCT) is important in low pH environments. Furthermore, our work shows that triplet oxygen and photo-produced species are the main oxidants of Fe(II) while hydrogen peroxide, a relatively stable end product of SRFA photolysis, is not involved in Fe(II) oxidation. A kinetic model based on these observations is presented which provides an excellent description of the experimental results and is consistent with observations from a wide range of studies investigating the redox cycling of iron.