Scavenging of dissolved organic matter (DOM) by amorphous iron hydroxide particles Fe(OH)3(s)

Scavenging of dissolved organic matter (DOM) by particulate metal oxides like Fe(OH)_3(s) is one of three processes that can influence the concentration and composition of DOM in aquatic systems. The other two possible processes include photodegradation and biodegradation. In combination, these processes alter the concentration and composition of DOM systematically with increasing time, measured as hydrologic residence time (HRT). The objective of this research was to determine the change in Fe(OH)_3(s)-scavengable dissolved organic carbon (DOC) with increasing HRT (0–80 yr). In addition, DOC from allochthonous and autochthonous sources were included in this study. The susceptibility of DOC from surface waters to scavenging by Fe(OH)_3(s) was found to decrease as a function of HRT, from approximately 90% to 79%. The lowest HRT system was operationally considered equivalent to allochthonous DOC, while autochthonous DOC was scavenged similarly to DOC from the 80 yr HRT system. These results indicate that scavenging of bulk DOC may be limited by metal loading in aquatic systems, and that the bulk of Fe(OH)_3(s)-reactive DOC is from allochthonous sources. In addition, all surface waters treated with Fe(OH)_3(s) contained approximately 1 mg l^–1 of DOC that was resistant to scavenging (SD = 0.50, n = 5), which suggests that a refractory fraction of DOC persists in surface waters.