On the equivalence of the power and reactive continuum models of organic matter diagenesis

Tarutis, William J.

doi:10.1016/0016-7037(93)90071-4

Cited by 31 publications

(15 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This result, obtained earlier by Tarutis (11), can be generalized. One need only assume that the initial distribution g(k,0) has an asymptotic expansion (12) for k→0 with leading order behavior g(k,0)~k…”

supporting

confidence: 80%

Response to Comment on "Physical Model for the Decay and Preservation of Marine Organic Carbon"

Rothman

Forney

2008

Science

View full text Add to dashboard Cite

Fast enzyme deactivation rates are not required by our physical model of organic matter decay. Instead, low effective diffusivities arising from sorption of enzymes and physical protection by minerals are sufficient. Our model predicts observed temporal trends in organic-matter decay rather than specific rate constants. Existing statistical models of intrinsic reactivity explain observed trends empirically but not theoretically. O ur physical model (1) for the decay of marine organic carbon assumes that organic matter differs only in its accessibility to microbial degradation but not its intrinsic reactivity. The model additionally assumes that a characteristic distance r b between microbes is much greater than the characteristic distance b . In other words, we require that the dimensionless quantity R ≡ br b >> 1, where b = (a/‾ D)1/2 and ‾ D is an effective diffusivity. Our fits to data suggest that R ≅ 5.6.The issue of inferred enzyme deactivation rates is more appropriately examined in terms of the length-scale ratio R. When R >> 1, steady-state spatial distributions of active enzymes are much more concentrated in the immediate vicinity of microbes than away from them. When R << 1, enzymes remain functional over a sufficiently long period of time such that steady-state diffusive gradients should be negligible. Recast in these terms, the argument of Boudreau et al. (2) suggests that typical known values of the quantities a, ‾ D, and r b are inconsistent with R >> 1, by at least two orders of magnitude. Their numbers instead suggest a well-mixed regime in which physical accessibility to enzymes is spatially homogeneous.In addressing this issue in our paper (1), we hypothesized that R = (a/‾ D) 1/2 r b >> 1 might derive from an effective diffusivity ‾ D that is much less than the bare diffusivity D cited by Boudreau et al. We suggested two mechanisms: shielding of organic matter in clay-rich aggregates and sorption of enzymes to surfaces.Sorption retards diffusive transport. A standard calculation (3) using characteristic sorption parameters (4) shows that ‾ D decreases by about two orders of magnitude. If sorbed enzymes deactivate at the same constant rate a as in solution, R then increases by a factor of about 10. In the extreme case of deactivation only and always upon sorption, a purely geometric calculation (5) based on a porosity of 0.8 and a typical specific surface area of 10 5 cm −1 (4) yields R~100. If, however, enzymes do not deactivate on surfaces (6), then a decreases with ‾ D and there is no effect on R. Shielding, proposed earlier by Mayer (7), implies a patchy distribution of organic matter that is to some extent physically protected by minerals. Consideration of diffusive transport in tight percolation networks (8) then provides a natural mechanism for locally driving ‾ D orders of magnitude below D, potentially increasing R by up to an order of magnitude or more.There are also questions concerning whether the relevant r b should be obtained from surface sediments or, for example, depths of met...

show abstract

supporting

confidence: 80%

Response to Comment on "Physical Model for the Decay and Preservation of Marine Organic Carbon"

Rothman

Forney

2008

Science

View full text Add to dashboard Cite

show abstract

“…However, Bosatta and Agren (1995) illustrated that their model of organic matter degradation, the q-theory, reduces to the reactive continuum model or the power model under specific assumptions. In addition, Tarutis (1993) showed that the reactive continuum model and the power model are mathematically equivalent for a simple closed-system decay (i.e. no bioturbation) if the reactive continuum model is based on a Gamma distribution and the exponent of power model equals one.…”

Section: Reaction Networkmentioning

confidence: 99%

Evolution of organic matter degradation in Cretaceous black shales inferred from authigenic barite: A reaction-transport model

Arndt

Hetzel²,

Brumsack³

2009

Geochimica et Cosmochimica Acta

View full text Add to dashboard Cite

“…Thus, the reactivity of bulk sedimentary organic matter is most accurately conceptualized and quantified as a weighted average of reactivities corresponding to a continuum of compositions and degradation states of sediment components rather than a single k (Boudreau and Ruddick, 1991). For reasonable assumptions regarding the nature of the reactivity distribution function, the reactive continuum model predicts the observed 1/t dependence of the apparent k observed for bulk sedimentary organic matter (Tarutis, 1993).…”

Section: Reaction Rates and Kineticsmentioning

confidence: 99%

Sedimentary Diagenesis, Depositional Environments, and Benthic Fluxes

Aller

2014

Treatise on Geochemistry

126

138

View full text Add to dashboard Cite

On the equivalence of the power and reactive continuum models of organic matter diagenesis

Cited by 31 publications

References 6 publications

Response to Comment on "Physical Model for the Decay and Preservation of Marine Organic Carbon"

Response to Comment on "Physical Model for the Decay and Preservation of Marine Organic Carbon"

Evolution of organic matter degradation in Cretaceous black shales inferred from authigenic barite: A reaction-transport model

Sedimentary Diagenesis, Depositional Environments, and Benthic Fluxes

Contact Info

Product

Resources

About