Department of Energy • Office of Science • Biological and Environmental Research1 BER Climate Research

Reactive transport modeling helps to understand model structures and evaluate relevant uncertainties.

ObjectiveA consistent modeling approach to belowground biogeochemical processes is lacking in climate-scale land models. To address this deficiency, we developed CLM4-BeTR, a multi-tracer, multi-phase biogeochemical transport and reaction module in CLM4 (and CLM4.5).

Research•We evaluated the transport algorithm

using two analytical solutions.•Using observations, we evaluated the

prevailing assumption that “surface CO2 efflux equals soil respiration”.•We performed component-wise

simulations to evaluate different respiration components and their impact on surface CO2 fluxes.

Impact•We conclude that the default 30 minute

time step is sufficient for accurate transport calculations in CLM4-BeTR.•The prevailing assumption regarding CO2

production and emissions did not hold at many temporal scales.•Allows for the use of a wider range of

measurements in ecosystem studies.Reference: Tang, J. Y., Riley, W. J., Koven, C. D., and Subin, Z. M.: CLM4-BeTR, a generic biogeochemical transport and reaction module for CLM4: model development, evaluation, and application, Geosci. Model Dev., 6, 127-140, doi:10.5194/gmd-6-127-2013, 2013.

Figure. Predicted soil CO2 concentrations.

Figure. CLM4-BeTR model structure.