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Increasing concentrations of iron in surface waters as a consequence of reducing conditions in the catchment area

Ekström, Sara M. LU ; Regnell, Olof LU ; Reader, Heather E. LU ; Nilsson, Anders LU ; Löfgren, Stefan and Kritzberg, Emma S. LU (2016) In Journal of Geophysical Research - Biogeosciences 121(2). p.479-493
Abstract

Recent studies report trends of strongly increasing iron (Fe) concentrations in freshwaters. Since Fe is a key element with a decisive role in the biogeochemical cycling of major elements, it is important to understand the mechanisms behind these trends. We hypothesized that variations in Fe concentration are driven mainly by redox dynamics in hydraulically connected soils. Notably, Fe(III), which is the favored oxidation state except in environments where microbial activity provide strong reducing intensity, has several orders of magnitude lower water solubility than Fe(II). To test our hypothesis, seasonal variation in water chemistry, discharge, and air temperature was studied in three Swedish rivers. Methylmercury and sulfate were... (More)

Recent studies report trends of strongly increasing iron (Fe) concentrations in freshwaters. Since Fe is a key element with a decisive role in the biogeochemical cycling of major elements, it is important to understand the mechanisms behind these trends. We hypothesized that variations in Fe concentration are driven mainly by redox dynamics in hydraulically connected soils. Notably, Fe(III), which is the favored oxidation state except in environments where microbial activity provide strong reducing intensity, has several orders of magnitude lower water solubility than Fe(II). To test our hypothesis, seasonal variation in water chemistry, discharge, and air temperature was studied in three Swedish rivers. Methylmercury and sulfate were used as indicators of seasonal redox changes. Seasonal variability in water chemistry, discharge, and air temperature in the Emån and Lyckeby Rivers implied that the variation in Fe was primarily driven by the prevalence of reducing conditions in the catchment. In general, high Fe concentrations were observed when methylmercury was high and sulfate was low, indicative of reducing conditions. The Fe concentrations showed no or weak relationships with variations in dissolved organic matter concentration and aromaticity. The seasonal variation in Fe concentration of the Ume river was primarily dependent on timing of the snowmelt in high- versus low-altitude areas of the catchment. There were long-term trends of increasing temperature in all catchments and also trends of increasing discharge in the southern rivers, which should increase the probability for anaerobic conditions in space and time and thereby increase Fe transport to the aquatic systems.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
biogeochemistry, dissolved organic matter, iron, redox dynamics, sulfur
in
Journal of Geophysical Research - Biogeosciences
volume
121
issue
2
pages
15 pages
publisher
American Geophysical Union
external identifiers
  • scopus:84959175790
  • wos:000373197300016
ISSN
2169-8953
DOI
10.1002/2015JG003141
language
English
LU publication?
yes
id
790ea211-6501-45d6-895d-5c37196da3e5
date added to LUP
2016-07-15 08:13:17
date last changed
2017-04-23 04:52:03
@article{790ea211-6501-45d6-895d-5c37196da3e5,
  abstract     = {<p>Recent studies report trends of strongly increasing iron (Fe) concentrations in freshwaters. Since Fe is a key element with a decisive role in the biogeochemical cycling of major elements, it is important to understand the mechanisms behind these trends. We hypothesized that variations in Fe concentration are driven mainly by redox dynamics in hydraulically connected soils. Notably, Fe(III), which is the favored oxidation state except in environments where microbial activity provide strong reducing intensity, has several orders of magnitude lower water solubility than Fe(II). To test our hypothesis, seasonal variation in water chemistry, discharge, and air temperature was studied in three Swedish rivers. Methylmercury and sulfate were used as indicators of seasonal redox changes. Seasonal variability in water chemistry, discharge, and air temperature in the Emån and Lyckeby Rivers implied that the variation in Fe was primarily driven by the prevalence of reducing conditions in the catchment. In general, high Fe concentrations were observed when methylmercury was high and sulfate was low, indicative of reducing conditions. The Fe concentrations showed no or weak relationships with variations in dissolved organic matter concentration and aromaticity. The seasonal variation in Fe concentration of the Ume river was primarily dependent on timing of the snowmelt in high- versus low-altitude areas of the catchment. There were long-term trends of increasing temperature in all catchments and also trends of increasing discharge in the southern rivers, which should increase the probability for anaerobic conditions in space and time and thereby increase Fe transport to the aquatic systems.</p>},
  author       = {Ekström, Sara M. and Regnell, Olof and Reader, Heather E. and Nilsson, Anders and Löfgren, Stefan and Kritzberg, Emma S.},
  issn         = {2169-8953},
  keyword      = {biogeochemistry,dissolved organic matter,iron,redox dynamics,sulfur},
  language     = {eng},
  month        = {02},
  number       = {2},
  pages        = {479--493},
  publisher    = {American Geophysical Union},
  series       = {Journal of Geophysical Research - Biogeosciences},
  title        = {Increasing concentrations of iron in surface waters as a consequence of reducing conditions in the catchment area},
  url          = {http://dx.doi.org/10.1002/2015JG003141},
  volume       = {121},
  year         = {2016},
}