The dependence of bacterial sulfate reduction on sulfate concentration in marine sediments

Kinetics of microbial Fe(III) oxide reduction in freshwater wetland sediments

“…This ex-CH O 2 pression is functionally identical to the framework used in recent diagenetic models of Fe(III) oxide reduction and other biogeochemical processes in aquatic sediments (Boudreau 1996;Van Cappellen and Wang 1996). In this framework, Fe(III) oxide reduction rates are assumed to first order with respect to Fe(III) Relationship between FeRB abundance and Fe(III) reduction kinetics-A MPN enumeration procedure employing synthetic growth medium was used to evaluate the potential importance of changes in FeRB population size to the response of microbial Fe(III) oxide reduction to addition of different amounts of labile OM.…”

“…Strictly speaking, the use of such simplifications is not appropriate in quantitative models of microbiologically catalyzed reactions in environmental systems (Rittman and Van Briesen 1996). However, this simplifying assumption is common (and often defensible) in geochemical models of sediment microbial processes (Boudreau 1992) and is used here in order to facilitate mechanistic interpretation of the overall kinetic response of microbial Fe(III) oxide reduction in TW sediments. As discussed further below, our knowledge of FeRB abundance is insufficient to permit accurate assessment of the importance of population size changes on apparent rate constants for microbial Fe(III) oxide reduction.…”

“…In order to evaluate this question in relation to Fe(III) oxide reduction in TW sediments, data from sediment slurry and surface sediment incubation experiments (Figs. 1 and 3) were pooled and analyzed according to the reactive continuum model of Aris (1989) as described by Boudreau and Ruddick (1991) and Postma (1993). The concentration of Fe(III) designated as being formally nonreactive on the time scale of the incubation experiments was subtracted from measured Fe(III) values prior to conducting the reactive continuum analysis.…”

“…Understanding the kinetics of microbial Fe(III) oxide reduction is a prerequisite for modeling carbon and energy flux through sedimentary Fe cycling and the impact of Fe(III) oxide reduction on other electron-accepting processes (Thamdrup 2000), as well as for predicting the fate of inorganic and organic contaminants whose behavior is linked to Fe redox chemistry (Van Cappellen and Wang 1995). To date there has been no definitive demonstration of the kinetics of this process, e.g., in a manner analogous to how the kinetics of bacterial sulfate reduction in marine sediments has been defined in relation to sulfate and particulate organic carbon concentration (Boudreau and Westrich 1984;Westrich and Berner 1984). Analysis of the kinetics of microbial Fe(III) reduction in sediments presents a unique problem relative to other terminal electronaccepting reactions (e.g., oxygen, nitrate, and sulfate reduction) because Fe(III) oxides are highly insoluble at circumneutral pH.…”

REMAP: A reaction transport model for isotope ratio calculations in porous media

“…where L is the substrate concentration value at which metabolic activity has dropped to 50% [see also Boudreau and Westrich, 1984]. Experimental results [Habicht et al, 2005] and theoretical considerations [Brunner and Bernasconi, 2005] suggest that a also depends on substrate concentration, which we implement in a similar way…”