Environmental and Water Resources

Department of Civil Engineering, Auburn University

SPEAKER: Dr. Eric E. Roden, Associate Professor, University of Alabama

TITLE: Experimental and modeling analysis of Fe redox cycling kinetics and the influence of microbial Fe(III) oxide reduction on methane production in freshwater wetland sediments

DATE: Friday, September 13, 2002

PLACE: Harbert 111 Department of Civil Engineering

TIME: 3:00 PM

SPEAKER INFO: Dr. Roden is an associate professor at the Department of Biological Sciences, University of Alabama. He received his PhD from Univ of Maryland and later worked at United States Geological Survey (USGS) and at the Battelle Pacific Northwest National Laboratory, Richland, Washington. His research interests include biogeochemistry of aquatic environments, emphasizing microbial metabolism in anaerobic soils and sediments.

ABSTRACT: The kinetics of microbial amorphous Fe(III) oxide reduction was investigated in surface sediments from a freshwater wetland in north central Alabama. Initial rates of Fe(III) oxide reduction were linearly correlated with initial Fe(III) oxide abundance in mixtures of Fe(III)-rich and Fe(III)-depleted sediment slurries, and in sediments from various depth intervals in the upper 3 cm of freshly collected cores. These findings provide explicit evidence that microbial Fe(III) oxide reduction rates are first-order with respect to amorphous Fe(III) oxide concentration in the wetland sediment. The observed first-order relationship between Fe(III) oxide concentration and reduction rate is consistent with established models of surface area-controlled mineral dissolution. An experiment in which Fe(III) oxide-rich sediment slurries were amended with different amounts of labile organic matter demonstrated a direct correlation between Fe(III) reduction rate constants and initial rates of organic carbon mineralization. A simple ‘modified Monod’ kinetic model was used to simulate patterns of Fe(III) oxide reduction and methanogenesis in this experiment. In addition, a multicomponent transport-reaction model simulating the interaction between Fe(III) oxide reduction and methanogenesis was developed to explain downcore patterns of Fe(III) oxide reduction and methane production in unvegetated surface sediments. A major feature of the model is its explicit inclusion of Fe redox cycling kinetics, including oxidation of aqueous and solid-phase Fe(II) within oxygen microgradients at the sediment-water interface. The model can be used to explore how changes in sediment Fe abundance and cycling intensity may influence the impact of Fe(III) reduction on methane release from different types of freshwater sediments.

Environmental and Water Resource (EWR) seminar series is organized by the Department of Civil Engineering. For details contact the seminar coordinators: Dr. Prabhakar Clement (clement@eng.auburn.edu or Tel: 334-844-6268) or Melissa McIndoe (mcindmj@auburn.edu)