Re-establishing of wetlands on former drained lowland areas used for agriculture has come into focus as a measure to reduce nutrient losses to the aquatic environment. However, new results have documented significant accumulations of iron bound phosphorus in Danish lowland soils (Kjaergaard et al., 2007). Thus, re-establishment of wetlands might constitute a risk of excess phosphorus loss to the aquatic environment, as changes in redox conditions may lead to reductive dissolution of iron(III) oxides and consequently release of iron bound phosphorus (Hoffmann et al., 2009). Groundwater and surface water interactions are of fundamental importance for the biogeochemical processes controlling phosphorus dynamics in wetlands, and different hydrological pathways such as groundwater discharge and surface water flooding are operating within wetlands (Hoffmann et al., 2009). During groundwater discharge water passes through the wetland sediment and carry soluble iron and phosphorus by convection to the sediment-water interface. During surface water flooding phosphorus fluxes from the sediment will be dominated by diffuse fluxes. The eventual loss of phosphorus mobilized within the anaerobic sediment depends both on the hydrological regimes and the processes taking place at the sediment-water interface. Re-oxidation of iron might allow a recapturing of phosphorus (Zak et al., 2004), and thereby impede P losses to the aquatic environment.
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Joint Meeting of Society of Wetland Scientists, WETPOL and Wetland Biogeochemistry Symposium, 2011