Dissolved iron speciation in two distinct river plumes and an estuary: Implications for riverine iron supply

Abstract

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 L 1 -type Fe-binding ligand class was measured in all surface samples, and in the Columbia River estuary. A weaker L 2 -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 5 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 L 1 -type ligand in nonestuarine (S . 13) surface samples. Leachable particulate (.0.4 mm) 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 L 1 -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 L 1 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.

Iron-binding ligands and their role in the ocean biogeochemistry of iron

“…2c shows the vertical distribution of strong Fe-binding ligand L 1 in the North-eastern Atlantic determined by electrochemical titrations by Boye et al [89] This would seem to make it unlikely that L 1 can represent siderophore-like compounds, which have relatively low molecular mass (300-1000 Da), [72] even though the apparent stability complexes of the L 1 ligands, and siderophores, are very similar. However, these contradictory observations can be resolved if the siderophores, upon release into seawater by microbes, become strongly associated with organic colloids, as recently suggested by Buck et al [90] Again, we will return to this important point later on.…”

“…As mentioned earlier, these L 1 , siderophore-like ligands most likely become rapidly associated with colloidal organic matter. [90] Such an association is required to reconcile their low molecular weights, and high conditional stability constants with the apparently colloidal nature of electrochemically determined strong ligands.…”

Iron biogeochemistry across marine systems – progress from the past decade

“…Powell and Wilson-Finelli (2003) though point out that the latter is of crucial importance for Fe transport in the Mississippi river plume. Likewise, Buck et al (2007) demonstrated the predominant importance L 1 type ligands for Fe transport into the sea from the Columbia River and San Francisco Bay plumes. The stability constants of these strong L 1 ligands are very similar to those reported by Laglera and van den Berg (2009) for Fe bound to fulvic acids, indicating the importance of these ligands in controlling the solubility of dissolved iron in riverine and coastal systems.…”

Synergistic effects of iron and temperature on Antarctic phytoplankton and microzooplankton assemblages

“…Total dissolved Fe concentrations were filtered through 0.4 µm track-etched polycarbonate filters (Nuclepore Whatman) and acidified to pH 1.7 with 4 mL −1 sub-boiled distilled HCl. Total dissolved Fe was measured using adsorptive cathodic stripping voltammetry (ACSV) (Buck et al, 2007). A 5 mM salicylaldoxime (SA: Aldrich, ≥98%) solution was first prepared in quartz-distilled methanol (Q-MeOH) and stored in the refrigerator.…”