Modeling greenhouse gas budget in the northern ecosystems using a process-based ecosystem model, VISIT

Accurately modelling carbon dioxide (CO₂) and methane (CH₄) fluxes in northern wetland, forest, and tundra ecosystems is important for predicting future global climate change trajectories. In this study, we simulated CO₂ and CH₄ fluxes of northern ecosystems using a process-based terrestrial ecosystem model, VISIT, which was refined by implementing key processes for northern ecosystems. These newly incorporated processes include dynamics of water table depth and temperature gradient within soil active layer. The model was calibrated and validated using CO₂ and CH₄ fluxes at various northern ecosystems, including fen, bog, lowland forest, tussock tundra, and wet tundra sites. The model parameters were determined for each ecosystem type. After incorporating new processes, simulation performance in terms of seasonal variation and magnitude of the carbon fluxes was improved at each site with the refined version of the model. This indicates the importance of incorporating the high-latitude processes into the model for accurately predicting the carbon fluxes at northern ecosystems. We found that simulated CH₄ production rate was highly sensitive to water table and thaw depths, indicating that accurate estimation of soil hydrological and physical conditions is critical to predict CH₄ flux in the northern ecosystems. Finally, we are planning to simulate and predict the carbon fluxes of whole Pan-Arctic ecosystems using the improved model.