Iron-binding ligands and humic substances in the San Francisco Bay estuary and estuarine-influenced shelf regions of coastal California

Dissolved iron (dFe) and organic dFe-binding ligands were determined in San Francisco Bay, California by competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-ACSV) along a salinity gradient from the freshwater endmember of the Sacramento River (salinity 26). A range of dFe-bind...

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Bibliographic Details
Published in:Marine chemistry 2015-07, Vol.173, p.183-194
Main Authors: Bundy, Randelle M., Abdulla, Hussain A.N., Hatcher, Patrick G., Biller, Dondra V., Buck, Kristen N., Barbeau, Katherine A.
Format: Article
Language:English
Subjects:
Aliphatic polycarboxylic compounds
Brackish
Cathodic stripping voltammetry
Coastal
Estuaries
Flocculation
Humic substances
Iron
Iron-binding ligands
Ligands
Marine
Marine chemistry
Mouth
Multiple analytical window
Organic matter
Proton nuclear magnetic resonance
Rivers
Salinity
Shelves
USA, California, San Francisco Bay
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Summary:Dissolved iron (dFe) and organic dFe-binding ligands were determined in San Francisco Bay, California by competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-ACSV) along a salinity gradient from the freshwater endmember of the Sacramento River (salinity 26). A range of dFe-binding ligand classes was simultaneously determined using multiple analytical window analysis, involving titrations with multiple concentrations of the added ligand, salicylaldoxime. The highest dFe and ligand concentrations were determined in the low salinity end of the estuary, with dFe equal to 131.5nmolL−1 and strong ligand (log KFeL,Fe′cond≥12.0) concentrations equal to 139.5nmolL−1. The weakest ligands (log KFeL,Fe′cond11.0) were tightly coupled to dFe throughout the estuary, with average excess ligand concentrations ([L]–[dFe]) equal to 0.5nmolL−1. Humic-like substances analyzed via both CLE-ACSV and proton nuclear magnetic resonance in several samples were found to be a significant portion of the dFe-binding ligand pool in San Francisco Bay, with concentrations ranging from 559.5μgL−1 to 67.5μgL−1 in the lowest and highest salinity samples, respectively. DFe-binding ligands and humic-like substances were also found in benthic boundary layer samples taken from the shelf near the mouths of San Francisco Bay and Eel River, suggesting estuaries are an important source of dFe-binding ligands to California coastal shelf waters. •Iron-binding ligands were measured using multiple analytical window electrochemical analysis.•The strongest iron-binding ligands were resistant to flocculation in San Francisco Bay.•Weaker iron–ligand complexes were scavenged at high salinities.•Humic substances comprised a significant portion of the ligand pool.•San Francisco Bay is a source of strong ligand complexes to shelf waters.
ISSN:0304-4203
1872-7581
DOI:10.1016/j.marchem.2014.11.005