Widespread Increases in Iron Concentration in European and North American Freshwaters

Research output: Contribution to journalArticle


Recent reports of increasing iron (Fe) concentrations in freshwaters are of concern, given the fundamental role of Fe in biogeochemical processes. Still, little is known about the frequency and geographical distribution of Fe trends or about the underlying drivers. We analyzed temporal trends of Fe concentrations across 340 water bodies distributed over 10 countries in northern Europe and North America in order to gain a clearer understanding of where, to what extent, and why Fe concentrations are on the rise. We found that Fe concentrations have significantly increased in 28% of sites, and decreased in 4%, with most positive trends located in northern Europe. Regions with rising Fe concentrations tend to coincide with those with organic carbon (OC) increases. Fe and OC increases may not be directly mechanistically linked, but may nevertheless be responding to common regional-scale drivers such as declining sulfur deposition or hydrological changes. A role of hydrological factors was supported by covarying trends in Fe and dissolved silica, as these elements tend to stem from similar soil depths. A positive relationship between Fe increases and conifer cover suggests that changing land use and expanded forestry could have contributed to enhanced Fe export, although increases were also observed in nonforested areas. We conclude that the phenomenon of increasing Fe concentrations is widespread, especially in northern Europe, with potentially significant implications for wider ecosystem biogeochemistry, and for the current browning of freshwaters.


  • Gesa A. Weyhenmeyer
  • C. D. Evans
  • Mark O. Gessner
  • H. P. Grossart
  • K. Kangur
  • I. Kokorite
  • P. Kortelainen
  • H. Laudon
  • J. Lehtoranta
  • N. Lottig
  • D. T. Monteith
  • P Nõges
  • T Nõges
  • F. Oulehle
  • G. C. Riise
  • J. A. Rusak
  • A. Räike
  • J. Sire
  • S. Sterling
External organisations
  • Centre for Ecology & Hydrology, Wallingford
  • Technical University of Berlin
  • Leibniz Institute of Freshwater Ecology and Inland Fisheries
  • University of Latvia
  • Finnish Environment Institute
  • Swedish University of Agricultural Sciences
  • University of Wisconsin-Madison
  • Norwegian University of Life Sciences
  • Dalhousie University
  • Uppsala University
  • University of Potsdam
  • Estonian University of Life Sciences - EMÜ
  • Czech Geological Survey (CGS)
  • Global Change Research Centre of the Czech Academy of Sciences
  • Dorset Environmental Science Centre
  • Latvian Environment, Geology and Meteorology Centre
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Geochemistry


  • Browning, Climate change, Freshwaters, Iron, Trends
Original languageEnglish
Pages (from-to)1488-1500
JournalGlobal Biogeochemical Cycles
Issue number10
Early online date2017 Oct 20
Publication statusPublished - 2017 Oct
Publication categoryResearch