The next generation of land models integrated in Earth System Models (ESMs), like the Community Land Model (CLM), will have horizontal gridcells with area ~o(100 km2) and soil vertical discretization ~o(cm) near the soil surface. Each of these dimensions are meant to subsume spatial heterogeneity that affect hydrological and biogeochemical cycles, but neither are close to the resolution of the fine-scale molecular transformations that impact carbon (C) and nitrogen (N) exchanges between terrestrial ecosystems and the atmosphere. In addition to issues associated with spatial scale, current ESM land models exclude representation of microbial and abiotic processes that mediate these fine-scale transformations. For example, there is currently sufficient research to suggest that the mechanistic 'resolution' for accurately modeling microbial dynamics and belowground biogeochemical transformations requires representation of microbial diversity. We will report here on model development, parameterization, testing, and application of an improved version of CLM that includes specific representation of trait-based microbial guilds, physical protection mechanisms (e.g., sorption), above- and belowground competition between plants and microbes for nutrients, and aqueous and gaseous transport. We also present a promising approach to represent horizontal spatial heterogeneity in hydrological dynamics with reduced order models based on fine-resolution simulations. Finally, model predictions are compared to observations from the ongoing Next Generation Ecosystem Experiment (NGEE)-Arctic campaign in Barrow, Alaska, and we discuss the compromises associated with increasing model complexity when insufficient observations exist to properly constrain parameters and model structures at the global scale.

Integrating fine-scale microbial dynamics, transport, and abiotic interactions into the global land model CLM4.5

247th National Meeting (2014)

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