Dissolved Iron Speciation in Two Distinct River Plumes and an Estuary: Implications for Riverine Iron Supply

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Dissolved iron (Fe) speciation in the Columbia River plume, the San Francisco Bay plume, and the Columbia River estuary was investigated using competitive ligand exchange‐adsorptive cathodic stripping voltammetry (CLE‐ACSV) with the added ligand salicylaldoxime. A stronger L1‐type Fe‐binding ligand class was measured in all surface samples, and in the Columbia River estuary. A weaker L2‐type ligand class was present in the far‐field Columbia River plume and the San Francisco Bay plume but was not observed in the low‐salinity (S = 1.4‐22.5) waters of the near‐field Columbia River plume or estuary. Concentrations of total dissolved Fe were correlated with the concentrations of the stronger L1‐type ligand in nonestuarine (S > 13) surface samples. Leachable particulate (>0.4 µm) Fe concentrations in the Columbia River plume were measured to supplement existing data from the San Francisco Bay plume. There is a large concentration of readily leachable particulate Fe in the two plumes, yet it is the concentration of ambient L1‐type ligands that appears to dictate the concentration of dissolved Fe in these waters and, consequently, the supply of dissolved Fe to neighboring coastal waters. The correlation between dissolved Fe and L1 ligand concentrations in both plume waters, as well as in California Current and upwelled surface waters, suggests that this relationship will persist in other coastal environments and should be considered when evaluating and modeling coastal Fe cycling and supply.

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Limnology and Oceanography, v. 52, issue 2, p. 843-855