Soil Iron Content as a Predictor of Carbon and Nutrient Mobilization in Rewetted Fens

• Published in: PloS one Vol. 11; no. 4; p. e0153166
• Main Authors: Emsens, Willem-Jan, Aggenbach, Camiel J S, Schoutens, Ken, Smolders, Alfons J P, Zak, Dominik, van Diggelen, Rudy
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 06-04-2016; Public Library of Science (PLoS)
• Subjects: Alkalinity; Ammonium; Biology; Biology and Life Sciences; Breakdown; Carbon; Carbon - chemistry; Cores; Decomposition; Dissolved organic carbon; Earth Sciences; Ecology; Ecology and Environmental Sciences; Ecosystem biology; Ecosystems; Electric Conductivity; Engineering and Technology; Environmental aspects; Environmental impact; Environmental quality; Eutrophication; Fens; Flooding; Floods; Greenhouse gases; Groundwater; Hydrogen-Ion Concentration; Inorganic carbon; Inorganic compounds; Iron; Iron - analysis; Iron content; Mineralization; Minerals - analysis; Nitrates; Nitrogen - analysis; Nutrient content; Nutrient sources; Nutrients; Nutrients in soil; Organic carbon; Organic matter; Oxygenation; Peatlands; Phosphorus; Phosphorus - analysis; Physical Sciences; Pore water; Regeneration; Restoration; Soil - chemistry; Soil carbon; Soil characteristics; Soil fertility; Soil nutrients; Soil sciences; Soils; Strong interactions (field theory); Surface water; Trends; Vegetation; Water level fluctuations; Water levels; Waterlogging; Wetlands; Belgium; Denmark; Netherlands
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0153166

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.