Modelling Hydrogen Uptake in Soil: Exploring the Role of Microbial Activity

Hydrogen (H2) gas acts as a secondary greenhouse gas, indirectly increasing the lifetime of methane in the atmosphere by competing for hydroxyl radicals that would otherwise react with methane to convert it to carbon dioxide and water. Soils are a major sink for atmospheric hydrogen, so it is important to predict hydrogen uptake at regional scales to understand its potential impact on atmospheric chemistry. Process-based models have been developed that estimate soil hydrogen uptake, primarily focusing on abiotic factors, such as soil moisture and temperature. Previous models relied on accurate porosity data, limiting their applicability for regional simulations. Later approaches used soil texture to estimate moisture influence but neglected soil organic carbon's role in controlling microbial activity. Our study introduces a new model of hydrogen release and uptake by soils (HORUS) for use at field to global scale, shifting from existing models by including the pivotal role of soil organic carbon in controlling microbial activity. Leveraging the power of established soil organic matter models to simulate potential microbial activity, we integrate soil moisture, temperature and potential microbial activity into the model. We evaluate the performance of HORUS using measurements from four studies of soil hydrogen uptake and compare predictions to established models. Our approach improves estimates of hydrogen deposition velocity (uptake rates) across datasets. Results demonstrate that incorporating potential microbial activity significantly improves the accuracy and transferability of hydrogen deposition velocity estimates between different soil types, underscoring the vital role of soil organic matter and microorganisms in this process.