Skip to main content
Research article - Peer-reviewed, 2022

Spruce forest afforestation leading to increased Fe mobilization from soils

Skerlep, Martin; Nehzati, Susan; Johansson, Ulf; Kleja, Dan B.; Persson, Per; Kritzberg, Emma S.


Increasing exports of Fe and DOC from soils, causing browning of freshwaters, have been reported in recent decades in many regions of the northern hemisphere. Afforestation, and in particular an increase of Norway spruce forest in certain regions, is suggested as a driver behind these trends in water chemistry. In this study, we tested the hypothesis that the gradual accumulation of organic soil layers in spruce forests, and subsequent increase in organic acid concentrations and acidity enhances mobilization of Fe. First generation Norway spruce stands of different ages (35, 61, 90 years) and adjacent arable control plots were selected to represent the effects of aging forest. Soil solutions were sampled from suction lysimeters at two depths (below organic soil layer and in mineral soil) during two years, and analyzed for Fe concentration, Fe speciation (XAS analysis), DOC, metals, major anions and cations. Solution Fe concentrations were significantly higher in shallow soils under older spruce stands (by 5- and 6-fold) than in control plots and the youngest forest. Variation in Fe concentration was best explained by variation in DOC concentration and pH. Moreover, Fe in all soil solutions was present as mononuclear Fe(III)-OM complexes, showing that this phase is dominating Fe translocation. Fe speciation in the soil was also analyzed, and found to be dominated by Fe oxides with minor differences between plots. These results confirmed that Fe mobilization, by Fe(III)-OM complexes, was higher from mature spruce stands, which supports that afforestation with spruce may contribute to rising concentrations of Fe in surface waters.


Iron; DOC; Soil biogeochemistry; Browning; Norway spruce; Afforestation

Published in

2022, volume: 157, number: 3, pages: 273-290
Publisher: SPRINGER

Authors' information

Skerlep, Martin
Lund University
Nehzati, Susan
Lund University
Swedish University of Agricultural Sciences, Unit for Field-based Forest Research
Swedish University of Agricultural Sciences, Department of Soil and Environment
Persson, Per
Lund University
Kritzberg, Emma S.
Lund University

Sustainable Development Goals

SDG15 Life on land

UKÄ Subject classification

Soil Science
Forest Science

Publication Identifiers


URI (permanent link to this page)