Predicting Soil Carbon Dynamics, Net Ecosystem Exchange, and Nitrous Oxide Emissions with the EPIC Model.

This presentation will update and provide examples of the latest development in the EPIC terrestrial ecosystem model. A process-based submodel of denitrification was added to EPIC and linked to the existing, Century-based carbon / nitrogen submodel. Every day during a simulation, EPIC calculates heterotrophic respiration based on carbon / nitrogen pool transformations and adjusted by environmental controls (e.g., temperature, water, mineral nitrogen). EPIC then calculates whether there is enough oxygen to accept the electrons generated by both microbial and root respiration. If oxygen is insufficient, then other nitrogen species (nitrate, nitrite, and nitrous oxide) act as electron acceptors following a competitive inhibition scheme. A ratio of electron accepted / electrons generated is used to correct microbial respiration. An hourly implementation of the gas transport equation is used to oxygen, carbon dioxide, and nitrous oxide across the gaseous phase of the soil layers and across the soil-atmosphere interface. Examples of model performance will be presented and discussed.