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Spring flood induced shifts in Fe speciation and fate at increased salinity

Herzog, S. D. LU ; Conrad, S.; Ingri, J.; Persson, P. LU and Kritzberg, E. S. LU (2019) In Applied Geochemistry 109.
Abstract

Rivers have traditionally been viewed as negligible sources of iron (Fe) to marine waters, as most Fe gets lost during estuarine mixing. However, recent findings demonstrate that Fe from boreal rivers display a higher resistance towards salinity-induced aggregation, presumably due to stabilizing interactions with organic matter. Previous studies have shown that Fe (oxy)hydroxides are selectively removed by aggregation processes, and that organic Fe complexes are less affected by increasing salinity. It has been further proposed that Fe speciation varies in response to seasonal differences in hydrology. In this study X-ray absorption spectroscopy (XAS) was used to determine the temporal variation in Fe speciation and the connection to Fe... (More)

Rivers have traditionally been viewed as negligible sources of iron (Fe) to marine waters, as most Fe gets lost during estuarine mixing. However, recent findings demonstrate that Fe from boreal rivers display a higher resistance towards salinity-induced aggregation, presumably due to stabilizing interactions with organic matter. Previous studies have shown that Fe (oxy)hydroxides are selectively removed by aggregation processes, and that organic Fe complexes are less affected by increasing salinity. It has been further proposed that Fe speciation varies in response to seasonal differences in hydrology. In this study X-ray absorption spectroscopy (XAS) was used to determine the temporal variation in Fe speciation and the connection to Fe stability in response to increasing salinity in two boreal rivers (Kalix and Råne River), with the purpose to better understand the fate of riverine Fe export. Sampling was done from winter pre-flood, over the spring flood, to post-flood conditions (early April until mid June). In addition, parallel analyses for Fe speciation and isotope composition (δ56Fe relative to IRMM-14) were made on river samples, as well as salinity-induced aggregates and the fraction remaining in suspension, with the main objective to test if δ56Fe reflect the speciation of Fe. The contribution of organically complexed Fe increased during spring flood compared to the pre- and post-flood, as did Fe transport capacity. However, since Fe (oxy)hydroxides were dominating throughout the sampling period, the seasonal variability was small. Interestingly, salinity-induced aggregation experiments revealed that Fe (oxy)hydroxides, which dominated aggregates, displayed lower δ56Fe than in the river samples Fe, while organic Fe complexes in suspension had higher δ56Fe values. The seasonal variability in Fe isotope signature could not be simply linked to Fe speciation, but was probably also influenced by variation in source areas of Fe and processes along the flow-path that alter both Fe speciation and isotopic composition.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Boreal, Fe (oxy)hydroxides, Fe geochemistry, Fe isotopes, Fe speciation, Organically complexed Fe, Salinity gradient, Sub-arctic, Transport capacity, XAS
in
Applied Geochemistry
volume
109
publisher
Elsevier
external identifiers
  • scopus:85070319579
ISSN
0883-2927
DOI
10.1016/j.apgeochem.2019.104385
language
English
LU publication?
yes
id
2bba2211-5e4e-486d-85de-f5d03e0c3c7d
date added to LUP
2019-08-29 14:13:05
date last changed
2019-09-11 04:23:10
@article{2bba2211-5e4e-486d-85de-f5d03e0c3c7d,
  abstract     = {<p>Rivers have traditionally been viewed as negligible sources of iron (Fe) to marine waters, as most Fe gets lost during estuarine mixing. However, recent findings demonstrate that Fe from boreal rivers display a higher resistance towards salinity-induced aggregation, presumably due to stabilizing interactions with organic matter. Previous studies have shown that Fe (oxy)hydroxides are selectively removed by aggregation processes, and that organic Fe complexes are less affected by increasing salinity. It has been further proposed that Fe speciation varies in response to seasonal differences in hydrology. In this study X-ray absorption spectroscopy (XAS) was used to determine the temporal variation in Fe speciation and the connection to Fe stability in response to increasing salinity in two boreal rivers (Kalix and Råne River), with the purpose to better understand the fate of riverine Fe export. Sampling was done from winter pre-flood, over the spring flood, to post-flood conditions (early April until mid June). In addition, parallel analyses for Fe speciation and isotope composition (δ<sup>56</sup>Fe relative to IRMM-14) were made on river samples, as well as salinity-induced aggregates and the fraction remaining in suspension, with the main objective to test if δ<sup>56</sup>Fe reflect the speciation of Fe. The contribution of organically complexed Fe increased during spring flood compared to the pre- and post-flood, as did Fe transport capacity. However, since Fe (oxy)hydroxides were dominating throughout the sampling period, the seasonal variability was small. Interestingly, salinity-induced aggregation experiments revealed that Fe (oxy)hydroxides, which dominated aggregates, displayed lower δ<sup>56</sup>Fe than in the river samples Fe, while organic Fe complexes in suspension had higher δ<sup>56</sup>Fe values. The seasonal variability in Fe isotope signature could not be simply linked to Fe speciation, but was probably also influenced by variation in source areas of Fe and processes along the flow-path that alter both Fe speciation and isotopic composition.</p>},
  articleno    = {104385},
  author       = {Herzog, S. D. and Conrad, S. and Ingri, J. and Persson, P. and Kritzberg, E. S.},
  issn         = {0883-2927},
  keyword      = {Boreal,Fe (oxy)hydroxides,Fe geochemistry,Fe isotopes,Fe speciation,Organically complexed Fe,Salinity gradient,Sub-arctic,Transport capacity,XAS},
  language     = {eng},
  month        = {10},
  publisher    = {Elsevier},
  series       = {Applied Geochemistry},
  title        = {Spring flood induced shifts in Fe speciation and fate at increased salinity},
  url          = {http://dx.doi.org/10.1016/j.apgeochem.2019.104385},
  volume       = {109},
  year         = {2019},
}