Reactive Flow and Transport Simulator GeoSysBRNS

Developing team: Florian Centler, Haibing Shao

The fate of chemical compounds in the subsurface is determined by a multitude of abiotic and biotic processes. Due to the complexity of these networks of interacting processes, an analysis is usually difficult. To disentangle them, numerical modeling has proved to be an indispensable tool. In simulation studies, hypothesis can be formulated, tested, and refined in the context of measured field data sets, both identifying the underlying process network, and yielding qualitative and quantitative predictions for the overall fate of a compound of interest.

Focusing on the saturated zone, the reactive flow and transport simulator GeoSysBRNS (coupling the flow and transport model OGS with the biogeochemical reaction network simulator BRNS) allows for the integrated simulation of groundwater flow, transport of chemically reactive species, and (bio-) chemical processes transforming them in up to three spatial dimensions. Flexibility with respect to the description of reactive transformation processes has been a priority during the development. Reactive species in GeoSysBRNS can refer to actual chemical compounds, or to pseudo-species. These can, for example, refer to microbial biomass of species catalyzing particular transformations, or to the isotopologically heavy fraction of an organic compound. Chemical and biochemical processes can be kinetically controlled (e.g., by Monod-kinetics), or are assumed to be at equilibrium (e.g., for acid base dissociations). A major advantage of GeoSysBRNS is its way of defining reactive processes: instead of providing a pre-defined fixed set of kinetics, or requiring the user to apply changes at the source code level, chemical processes are written as ordinary differential equations of arbitrary form in the Maple environment. An easy Drag&Drop operation performs the required generation of Fortran source code and the subsequent compilation of the process network specification to a dynamic link library. This flexibility is obtained by employing an operator-splitting scheme, and allows for fast development times for the setup of new scenarios.

As an application example, GeoSysBRNS has been used to investigate the concurrent stable isotope fractionation in both carbon and hydrogen during benzene biodegradation (Fig. 1, Centler et al. 2013)

Example of a GeoSysBRNS application
Figure 1: An exemplary application of GeoSysBRNS: simulating a benzene plume undergoing microbial degradation via both aerobic and anaerobic pathways leading to different shifts in the isotope signatures (contour lines) for carbon (top) and hydrogen (bottom).

Publications

Centler, F., He├če, F., Thullner, M., (2013): Estimating pathway-specific contributions to biodegradation in aquifers based on dual isotope analysis: theoretical analysis and reactive transport simulations, J. Contam. Hydrol. 152 , 97 - 116

Centler, F., Shao, H., De Biase, C., Park, C.-H., Regnier, P., Kolditz, O., Thullner, M., (2010): GeoSysBRNS-A flexible multidimensional reactive transport model for simulating biogeochemical subsurface processes, Comput. Geosci. 36 (3), 397 - 405