Regulators of heterotrophic microbial potentials in wetland soils

Potential rates of aerobic respiration, denitri®cation, sulfate reduction and methanogenesis were investigated in 10 di€erent wetland soils with a wide range of biogeochemical characteristics, with the objective of determining relationships between process rates and soil properties. Electron acceptor amendments to methanogenic soils caused gradual (1±13 d) to immediate transitions in electron ̄ow from methanogenesis to alternate electron acceptors. Rates of organic C mineralization ranged between 0.2 and 34 mmol C gÿ1 dÿ1 and averaged three times faster with O2 as compared to alternate electron acceptors. There was no signi®cant di€erence between rates of organic C mineralization (CO2+CH4 production) under denitrifying, sulfatereducing and methanogenic conditions, indicating that soil organic carbon availability was similar under the di€erent anaerobic conditions. Rates of electron acceptor consumption ranged between 1 and 107 mmol gÿ1 dÿ1 for O2, 0.5 and 9.3 mmol g ÿ1 dÿ1 for NO3 ÿ , 0.1 and 11.1 mmol gÿ1 dÿ1 for SO4 2ÿ and 0.1 and 6.2 mmol gÿ1 dÿ1 for CO2. Heterotrophic potentials in wetland soils were strongly correlated with inorganic N and several available C indices (total, dissolved and microbial C), but not with pH or dissolved nutrients (P, Ca, Mg, Fe(II)). Microbial activity±soil property relationships determined in this study may be useful for predicting the fate of pollutants that are in ̄uenced by microbial oxidation±reduction reactions in di€erent types of wetland soils. # 1999 Elsevier Science Ltd. All rights reserved.