Effect of dissolved organic carbon on 59Fe scavenging

The scavenging rates of tracer 59Fe via sedimentation and loss rates of dissolved organic C (DOC) from limnocorrals containing different proportions of DOC‐rich stream water and DOC‐poor lake water were measured. 59Fe scavenging rates were inversely correlated with concentration of DOC, decreasing by a factor of four as DOC increased from 550 to 1,550 µmol liter−1. In contrast to Fe, the loss rates for DOC increased with increasing DOC concentration; thus the mechanisms for loss of Fe and DOC appeared to be different. The effect of DOC on Fe scavenging was consistent with competition between organic ligands and particles for aqueous Fe and with DOC‐enhanced colloid stability. Fe scavenging was poorly related to particle concentration and settling velocity.