Temperature and moisture dependence of soil H2 uptake measured in the laboratory

The soil sink of molecular hydrogen is the largest and most uncertain term in the global atmospheric H-2 budget. Lack of information about the mechanisms regulating this sink limits our ability to predict how atmospheric H-2 may respond to future changes in climate or anthropogenic emissions. Here we present the results from a series of laboratory experiments designed to systematically evaluate and describe the temperature and soil moisture dependence of H-2 uptake by soils from boreal forest and desert ecosystems. We observed substantial H-2 uptake between -4 degrees C and 0 degrees C, a broad temperature optimum between 20 degrees C and 30 degrees C, a soil moisture optimum at approximately 20% saturation, and inhibition of uptake at both low and high soil moisture. A sigmoidal function described the temperature response of H-2 uptake by soils between -15 degrees C and 40 degrees C. Based on our results, we present a framework for a model of the soil H-2 sink.