title: Iron concentrations are increasing in surface waters from forested headwater catchments in eastern Finland.
abstract: Observations of increased water colour have been made in lakes and rivers all across the northern mid-latitudes of Europe and North America, particularly during the last 10-20 yr. This water browning or brownification has been attributed to the increased organic carbon concentrations due to climate change and decreased acid atmospheric deposition. Given that iron (Fe) may also increase water colour, the contribution of Fe to water brownification has received small attention. Our aim was to study the temporal trends of Fe in forested headwater catchments in eastern Finland, where an increasing air temperature and total organic carbon (TOC) trend had been observed in an earlier study. We found a statistically significant increasing trend also in stream water Fe concentrations and a strong correlation between the trends of TOC and Fe. The average increase in TOC and Fe concentrations between 1995 and 2006 was 0.5 mg l(-1) yr(-1) (2.5%), and 34.6 μ gl(-1) yr(-1) (3.5%), respectively. These results indicate that the increased water colour or brownification in Northern Europe may not only be due to increased concentrations of organic matter but also increased concentrations of Fe. The change in precipitation and temperature conditions, particularly during late autumn and early winter periods, appeared to be the main environmental factor behind increasing Fe trends. The strong correlation between the trends of Fe and TOC indicated that the increased Fe-organic matter complexation is the mechanism behind increasing Fe trends, but further research is needed to assess the chemical forms of increased Fe that coupled with increased TOC concentrations would enhance water brownification.
authors.affiliation: Finnish Forest Research Institute, P.O. Box 68, FI-80101 Joensuu, Finland. Electronic address: sakari.sarkkola@metla.fi.
authors.forename: Sakari
authors.initials: S
authors.lastname: Sarkkola
authors.forename: Mika
authors.initials: M
authors.lastname: Nieminen
authors.forename: Harri
authors.initials: H
authors.lastname: Koivusalo
authors.forename: Ari
authors.initials: A
authors.lastname: Laurén
authors.forename: Pirkko
authors.initials: P
authors.lastname: Kortelainen
authors.forename: Tuija
authors.initials: T
authors.lastname: Mattsson
authors.forename: Marjo
authors.initials: M
authors.lastname: Palviainen
authors.forename: Sirpa
authors.initials: S
authors.lastname: Piirainen
authors.forename: Mike
authors.initials: M
authors.lastname: Starr
authors.forename: Leena
authors.initials: L
authors.lastname: Finér
keywords: Brownification; Fe concentration; Peatland; TOC concentration; Time series; Trend analysis