Objective

1. Reactive transport modeling helps to understand model structures and evaluate relevant uncertainties. Figure. CLM4-BeTR model structure. Objective A 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). Figure. Predicted soil CO2 concentrations. • 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 CO2production 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.