Quantifying iron, manganese, and carbon fluxes in near-surface horizons of palustrine wetlands

Morphologic features indicative of a wet soil environment form in response to the concentration or depletion of Fe, Mn, and C. The time frame and environmental conditions necessary for the formation of such features is in question. We investigated the fluxes of Fe, Mn, and organic C, and the related hydromorphic features, in four wetlands on the Virginia Coastal Plain. Temperature, redox potential, and water table fluctuation were monitored on a monthly basis. Soil materials of a known composition were packed and constructed to form a soil structural unit, or simulated ped, and buried at a 15-cm depth in the wetlands. Interior and exteriors of the simulated peds were sampled and described after 1 and 2 yr in the wetlands. Wetland soils were above 5°C, saturated, and in a reducing environment most of the year. Simulated peds amended with organic matter contained considerably more roots after 2 yr than those peds that did not receive organic matter additions. In peds amended with organic matter, organic C levels dropped at approximate rates of 2 to 5 g kg-1 per year. Unamended ped interiors showed a slight increase in organic C over time (\u3c0.5 g kg-1/yr). Ped exteriors showed a higher rate of gain (1-2 g kg-1/yr). Levels of dithionite-citrate-bicarbonate (DCB)-extractable Mn dropped in the simulated peds at approximate rates of 5 to 15 mg kg-1 per year. Simulated peds amended with organic matter showed losses of DCB-extractable Fe on the order of 0.5 to 1.0 g kg-1 per year. Peds that were not amended, however, showed an increase in DCB Fe levels at rates as high as 2 g kg-1 per year. Observable hydromorphic features formed in less than 2 yr. The most prominent features were organic matter coatings and Fe masses on ped exteriors, and iron pore linings and depletions in the ped interiors