Grant: Discovery Grants Program - Individual

Dissolved organic carbon (DOC) is one of the most important mobile types of carbon environmentally, because it can become stabilized in soils. Increasing evidence shows that soil effects are dominating carbon cycling processes, particularly in relation to DOC. Storing DOC in soil is thus an approach to mitigate global warming. However, directly measuring how DOC is stored and moves in soil and how water, DOC, and microbes interact below ground is very difficult. Moreover, soil architectures and microbial activities are spatially heterogeneous from the micro-scale to the field scale. Consequently, many questions remain regarding DOC at the soil-pore scale. For example, is the pore scale merely an environment in which DOC adsorbs or desorbs to soil aggregates, or do the local microbe-water-DOC-pore structure interactions have emergent phenomena unique to this scale? Are there any phenomena at this scale that cannot be addressed in large-scale process-based models and interpretations? The pore scale is important because biogeochemical processes such as water-microorganism-DOC interactions and transport occur within the pores of the soil, giving rise to new biogeochemical behaviour that might not be understood or predicted by considering smaller or larger scales alone. Therefore, quantifying the changes happening in soil pores will be crucial for understanding the dynamics of DOC stabilization. This proposal aims to understand how processes that stabilize DOC are driven by water content and flow, spatial heterogeneity in soils, the availability and movement of DOC, and microbial activities in soils. We will simulate all these processes using the lattice Boltzmann model (LBM) embedded with an individual-based model (iBM) and the Dual Arrhenius and Michaelis-Menten (DAMM) kinetics model. The lattice Boltzmann codes we have already developed will provide a mathematical framework to simulate multi-species transport and degradation (e.g., DOC, water, oxygen, and product) at the soil-pore scale. The iBM will enable us to simulate microorganism growth and nutrient consumption and to set up experiments for the validation of the model. This analysis of the system will be based on the fundamental laws of physics, chemistry, and biology; it will enforce quantitative and comprehensive clarification of concepts and assumptions; and it will impose rational methods for approaching the problem. Our results will provide not only a detailed comparison of DOC stabilization in homogeneous and heterogeneous soil architectures but also quantifying influence of soil heterogeneity on DOC stabilization calculated using the DAMM. This knowledge could help to mitigate global warming by enabling the storage of greater levels of DOC in soil.