Oxygen depletion and phosphorus release following flooding of a cultivated wetland area in Denmark

Geografisk Tidsskrift, Danish Journal of Geography 108(2):17–25, 2008 The rewetting of altered wetlands is becoming increasingly widespread. When flooding cultivated soils, the oxygen (O2) availability is reduced, subsequently, ferric hydroxides can dissolve and associated inorganic phosphorus (P) will be mobilized. This study shows the temporal and spatial dynamics of O2 depletion following flooding using planar optodes and the subsequent release of Fe and P in two depth intervals in an experimental column set-up. The column was kept flooded for 48 days and thereafter partly drained and flooded again. Results document that large amounts of P (0.2 t P ha-1) have accumulated in the present plough-layer (Ap) during the last 22 years, which represent roughly 15% of the present inorganic P stock in the Ap. As a result of flooding, fully anoxic conditions were observed within 3 days (within 10 h in Ap) and concentrations of dissolved Fe and P in the soil solution increased simultaneously after 7 days of flooding. Thus, P reaction kinetics was markedly delayed as compared to O2 availability. P concentrations in soil water afterflooding (up to 0.15 mg L−1) accounted for only 0.034% of the inorganic P stock in the Ap which is a significantly smaller fraction of the potential P-release as compared to previous investigations. This is considered a result of only a minor fraction of the total inorganic P being directly associated with ferric hydroxides and thereby sensitive to short-term anoxic conditions as well as differences in the methodology used in this study (soil/water ratio). Finally, reactions releasing Fe and P were noted to be partly reversible upon draining. Keywords: Wetlandfloodingoxygen depletionplanar optodesphosphorusÅmosenDenmark

Anoxic waters · Biology · Ferric · Flooding (psychology · Oxygen · Phosphate · Phosphorus · Soil water · Water column · Biochemistry · Chemistry · Ecology · Environmental Chemistry · Environmental Science · Inorganic Chemistry · Peatlands and Wetlands Ecology · Soil and Water Nutrient Dynamics · Soil erosion and sediment transport · Soil Science

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