Tuesday, November 14, 2006 - 1:55 PM

Dynamics of Major Biogeochemical Processes in Soils from Reducing to Oxidizing Conditions.

Kewei Yu1, Frank Böhme2, Jörg Rinklebe2, Heinz Neue3, and Ronald DeLaune1. (1) Wetland Biogeochemistry Inst., Louisiana State Univ., Baton Rouge, LA 70803, (2) UFZ Centre for Environmental Research Leipzig-Halle, Dept. of Soil Chemistry, Theodor-Lieser-Str. 4, Halle/Saale, Germany, (3) GERMANY, UFZ-Cntr. of Env. Res., UFZ-Dept. of Soil Chemistry, Theodor-lieser-strasse 4, Halle, D-06120, GERMANY

Production of trace gases (CO2, CH4, and N2O) and transformation of N, S and metals (Fe and Mn) were studied in rice soil suspensions incubated from reducing to oxidizing conditions, using an automatic microcosm system. Results show that soil pH variation was inversely correlated to soil Eh change (P < 0.001). Soil CO2 production exponentially increased with soil Eh increase. In contrast, soil CH4 production showed an exponential decrease with soil Eh increase. Without inhibition by the presence of soil oxidants, methanogenesis occurred over the entire Eh range with likely H2-supported methanogenesis at higher soil Eh conditions constituting up to 20% of total CH4 production. Significant N2O production was observed between +200 to +500 mV attributed primarily to denitrification activities. Nitrification could also contribute to N2O production at a soil Eh above +500 mV, a possible critical Eh for the initiation of nitrification. The critical Eh for substantial immobilizing Fe and Mn was estimated to be around +50 and +250 mV, respectively. The intermediate Eh range (-150 to +180 mV) provided optimum conditions for minimizing cumulative global warming potential resulting from CO2, CH4 and N2O production in soils. To some extent, a soil incubation from reducing to oxidizing conditions mimics the Earth’s billions years history, which went from an early anoxic to the current oxidizing environment.