Upscaling & Heterogeneity

Heterogeneity in both space and time is a characteristic of most natural environments. It depends on the scale of interest which determines the necessary detail required in the model. Comparing results from models of different complexity allows to address the acceptable level of simplicity . Furthermore, interpolation of model results encompassing different spatial scales can lead to establishment of upscaling laws.

Micromodels
Models of porous media commonly employ a continuum description of reaction and transport processes, based on the notion of a representative elementary volume. However, if the reactant distribution at the pore scale is inhomogeneous, this can lead to considerable errors in estimates of reaction rates (Raje and Kapoor 2000). We have developed micromodels, explicitly resolving individual grains to address this issue (Meile and Tuncay, 2005).

Microbial metabolism
Microbes are the principle drivers of elemental turnover, as the biologically catalyzed reaction rates often exceed the abiotic chemical transformations by orders of magnitudes. To date, in most reactive transport models, microbes are treated in a very rudimentary fashion, e.g. as black boxes or using a biomass formulation, without taking into account details of their metabolism. However, with the onset of genetics and microbial ecology, a wealth of information becomes available that can be exploited and incorporated in RTMs. For more detailed information on models of cell metabolism see e.g. the Center for Cell and Virus Theory at IUB.

Simulated pore structures (Meile and Tuncay 2005) and sulfate reducers on mineral surfaces (Y. van Lith).

References:
Meile, C. and Tuncay, K. 2005. Scale dependence of reaction rates in porous media. Advances in Water Resources, in press.
Raje D. S. and Kapoor V. 2000. Experimental study of bimolecular reaction kinetics in porous media. Environ. Sci. Technol. 34(7), 1234-1239.