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Dissolved iron(II) ligands in river and estuarine water

Dissolved iron(II) ligands in river and estuarine water
Dissolved iron(II) ligands in river and estuarine water
We present the first evidence of Fe(II) complexation by natural organic ligands in estuarine waters. Across five diverse river/estuary systems we find evidence of terrestrially derived ligands with binding constants (log KFe(II)L) mainly in the range 6–8. These Fe(II) ligands were stable over short time periods (1–2 days), generally equivalent to, or in excess of, ambient freshwater Fe(II) concentrations (which ranged from 12 to 3600 nM) and had similar binding constants to ligands that were leached by water from vegetation and detritus (log KFe(II)L 7–8). A class of terrestrially derived ligands may therefore be important in stabilising Fe(II) concentrations in freshwater systems. However, in coastal seawater the impact of these ligands upon Fe(II) speciation is likely to be diminished due to a combination of dilution, loss of humic material during flocculation and increased ionic strength.

The temperate and sub-tropical river systems studied included the Beaulieu (England), Itchen (England), Cape Fear (North Carolina, USA), Winyah Bay (South Carolina, USA) and Loch Etive (Scotland). Freshwaters in each system possessed a broad range of dissolved organic carbon (DOC, 200–1300 ?M), labile dissolved Fe (LDFe, Fe < 0.2 ?m available to ferrozine after reduction with ascorbic acid, 100 nM–20 ?M) and pH (5.5–8.5). In the Itchen estuary, where anthropogenic discharge constitutes > 10% of freshwater input, ligand binding constants were elevated (up to log KFe(II)L 11) and the expected decrease in LDFe with increasing salinity along the estuary was not observed (LDFe and DOC both peaked at a salinity of 7) due to effluent inputs.
Iron, Ligands, Fe(II), Dissolved organic material
0304-4203
173-182
Hopwood, M.J.
43490323-6890-4689-91de-5e5f1ffe07b6
Statham, P.J.
51458f15-d6e2-4231-8bba-d0567f9e440c
Skrabal, S.A.
b708b1bb-ae06-4a4e-8728-3c10bb1dffb5
Willey, J.D.
9c12499e-a443-4f31-8783-5394a5a20d03
Hopwood, M.J.
43490323-6890-4689-91de-5e5f1ffe07b6
Statham, P.J.
51458f15-d6e2-4231-8bba-d0567f9e440c
Skrabal, S.A.
b708b1bb-ae06-4a4e-8728-3c10bb1dffb5
Willey, J.D.
9c12499e-a443-4f31-8783-5394a5a20d03

Hopwood, M.J., Statham, P.J., Skrabal, S.A. and Willey, J.D. (2015) Dissolved iron(II) ligands in river and estuarine water. Marine Chemistry, 173, 173-182. (doi:10.1016/j.marchem.2014.11.004).

Record type: Article

Abstract

We present the first evidence of Fe(II) complexation by natural organic ligands in estuarine waters. Across five diverse river/estuary systems we find evidence of terrestrially derived ligands with binding constants (log KFe(II)L) mainly in the range 6–8. These Fe(II) ligands were stable over short time periods (1–2 days), generally equivalent to, or in excess of, ambient freshwater Fe(II) concentrations (which ranged from 12 to 3600 nM) and had similar binding constants to ligands that were leached by water from vegetation and detritus (log KFe(II)L 7–8). A class of terrestrially derived ligands may therefore be important in stabilising Fe(II) concentrations in freshwater systems. However, in coastal seawater the impact of these ligands upon Fe(II) speciation is likely to be diminished due to a combination of dilution, loss of humic material during flocculation and increased ionic strength.

The temperate and sub-tropical river systems studied included the Beaulieu (England), Itchen (England), Cape Fear (North Carolina, USA), Winyah Bay (South Carolina, USA) and Loch Etive (Scotland). Freshwaters in each system possessed a broad range of dissolved organic carbon (DOC, 200–1300 ?M), labile dissolved Fe (LDFe, Fe < 0.2 ?m available to ferrozine after reduction with ascorbic acid, 100 nM–20 ?M) and pH (5.5–8.5). In the Itchen estuary, where anthropogenic discharge constitutes > 10% of freshwater input, ligand binding constants were elevated (up to log KFe(II)L 11) and the expected decrease in LDFe with increasing salinity along the estuary was not observed (LDFe and DOC both peaked at a salinity of 7) due to effluent inputs.

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More information

Published date: 5 July 2015
Keywords: Iron, Ligands, Fe(II), Dissolved organic material
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 372377
URI: http://eprints.soton.ac.uk/id/eprint/372377
ISSN: 0304-4203
PURE UUID: bb640020-4c9b-4913-a160-4a1729ae34b6

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Date deposited: 02 Dec 2014 10:22
Last modified: 27 Apr 2022 06:16

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Contributors

Author: M.J. Hopwood
Author: P.J. Statham
Author: S.A. Skrabal
Author: J.D. Willey

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