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 used as indicators of seasonal redox changes. Seasonal variability in water chemistry, discharge, and air temperature in the Eman 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.

Keywords

iron; redox dynamics; biogeochemistry; dissolved organic matter; sulfur

Published in

Journal of Geophysical Research: Biogeosciences
2016, Volume: 121, number: 2, pages: 479-493
Publisher: AMER GEOPHYSICAL UNION

SLU Authors

• Löfgren, Stefan

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

Associated SLU-program

Use of FOMA data


Sustainable Development Goals

SDG6 Ensure availability and sustainable management of water and sanitation for all


UKÄ Subject classification

Geochemistry
Environmental Sciences
Oceanography, Hydrology, Water Resources


Publication identifier

DOI: https://doi.org/10.1002/2015JG003141

Permanent link to this page (URI)

https://res.slu.se/id/publ/76805