title: Soil Iron Content as a Predictor of Carbon and Nutrient Mobilization in Rewetted Fens.
abstract: Rewetted, previously drained fens often remain sources rather than sinks for carbon and nutrients. To date, it is poorly understood which soil characteristics stimulate carbon and nutrient mobilization upon rewetting. Here, we assess the hypothesis that a large pool of iron in the soil negatively affects fen restoration success, as flooding-induced iron reduction (Fe3+ to Fe2+) causes a disproportionate breakdown of organic matter that is coupled with a release of inorganic compounds. We collected intact soil cores in two iron-poor and two iron-rich drained fens, half of which were subjected to a rewetting treatment while the other half was kept drained. Prolonged drainage led to the mobilization of nitrate (NO3-, > 1 mmol L-1) in all cores, regardless of soil iron content. In the rewetted iron-rich cores, a sharp increase in pore water iron (Fe) concentrations correlated with concentrations of inorganic carbon (TIC, > 13 mmol L-1) and dissolved organic carbon (DOC, > 16 mmol L-1). Additionally, ammonium (NH4+) accumulated up to phytotoxic concentrations of 1 mmol L-1 in the pore water of the rewetted iron-rich cores. Disproportionate mobilization of Fe, TIC, DOC and NH4+ was absent in the rewetted iron-poor cores, indicating a strong interaction between waterlogging and iron-mediated breakdown of organic matter. Concentrations of dissolved phosphorus (P) rose slightly in all cores upon rewetting, but remained low throughout the experiment. Our results suggest that large pools of iron in the top soil of drained fens can hamper the restoration of the fen's sink-service for ammonium and carbon upon rewetting. We argue that negative effects of iron should be most apparent in fens with fluctuating water levels, as temporary oxygenation allows frequent regeneration of Fe3+. We conclude that rewetting of iron-poor fens may be more feasible for restoration.
authors.affiliation: Ecosystem Management Research Group, Department of Biology, University of Antwerp, Universiteitsplein 1C, 2610 Wilrijk, Belgium.
authors.forename: Willem-Jan
authors.initials: WJ
authors.lastname: Emsens
authors.affiliation: Ecosystem Management Research Group, Department of Biology, University of Antwerp, Universiteitsplein 1C, 2610 Wilrijk, Belgium.|KWR Watercycle Research Institute, P.O. Box 1072, 3430 BB Nieuwegein, The Netherlands.
authors.forename: Camiel J S
authors.initials: CJ
authors.lastname: Aggenbach
authors.affiliation: Ecosystem Management Research Group, Department of Biology, University of Antwerp, Universiteitsplein 1C, 2610 Wilrijk, Belgium.
authors.forename: Ken
authors.initials: K
authors.lastname: Schoutens
authors.affiliation: Department of Aquatic Ecology and Environmental Biology, Institute for Wetland and Water Research, Radboud University Nijmegen, Heyendaalseweg 135 1, NL-6525 ED Nijmegen, The Netherlands.|B-WARE Research Centre, Toernooiveld 1, 6525 ED Nijmegen, the Netherlands.
authors.forename: Alfons J P
authors.initials: AJ
authors.lastname: Smolders
authors.affiliation: Chemical Analytics and Biogeochemistry, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, D-12587 Berlin, Germany.|Department of Bioscience, Aarhus University, Vejlsøvej, 8600 Silkeborg, Denmark.
authors.forename: Dominik
authors.initials: D
authors.lastname: Zak
authors.affiliation: Ecosystem Management Research Group, Department of Biology, University of Antwerp, Universiteitsplein 1C, 2610 Wilrijk, Belgium.
authors.forename: Rudy
authors.initials: R
authors.lastname: van Diggelen
mesh_terms: D002244:Carbon / Q000737:chemistry*; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000032:analysis*; D008903:Minerals / Q000032:analysis; D009584:Nitrogen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D012987:Soil / Q000737:chemistry*; D053833:Wetlands
chemical_list: D008903:Minerals; D012987:Soil; D010758:Phosphorus; D002244:Carbon; D007501:Iron; D009584:Nitrogen