Abstract Wetland soils may act as sinks for phosphorus from
agricultural soils but P sorption is sensitive to soil redox
conditions. When soils become flooded and anoxic, FeIII is
reduced and P sorption decreases. To get improved knowledge
about the relationship between redox state and P solubility
under field conditions, a grid of 4×5 sampling points laid out
in an Fe-rich meadow soil bordering a Danish river were
monitored during 11 weeks in the spring comprising in total
five sampling dates. The redox state was quantified as the
degree of Fe reduction (DRFe), i.e. percentage of soluble plus
sorbed FeII to total pedogenic, non-silicate Fe. Average DRFe
was highest (76 %) at beginning of April and decreased to
36 % within 9 weeks. The temporal and spatial variation of
DRFe and the soil solution concentrations of Fe and P were
high. Thus, average P in solution (Psol) ranged from 24 to
4 μM, closely correlated with average DRFe (R2=0.83). Soils
farthest away from the river drained first and hence exhibited
the biggest change in DRFe and Psol over time. The study
demonstrates the great spatial and temporal variability of
redox state and P solubility in such wetlands. Some likely
consequences of redox oscillations are indicated.