Quantifying the soil sink of atmospheric hydrogen: a full year of field measurements from grassland and forest soils in the UK
<p>Emissions of hydrogen (H<span class="inline-formula"><sub>2</sub></span>) gas from human activities are associated with indirect climate warming effects. As the hydrogen economy expands globally (e.g. the use of H<span class="inline-formula">...
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| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-07-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/22/3449/2025/bg-22-3449-2025.pdf |
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| Summary: | <p>Emissions of hydrogen (H<span class="inline-formula"><sub>2</sub></span>) gas from human activities are associated with indirect climate warming effects. As the hydrogen economy expands globally (e.g. the use of H<span class="inline-formula"><sub>2</sub></span> gas as a fuel), the anthropogenic release of H<span class="inline-formula"><sub>2</sub></span> into the atmosphere is expected to rise rapidly as a result of increased leakage. The dominant H<span class="inline-formula"><sub>2</sub></span> removal process is uptake into soils; however, removal mechanisms are poorly understood, and the fate and impact of increased H<span class="inline-formula"><sub>2</sub></span> emissions remain highly uncertain. Fluxes of H<span class="inline-formula"><sub>2</sub></span> within soils are rarely measured, and data to inform global models are based on few studies. This study presents soil H<span class="inline-formula"><sub>2</sub></span> fluxes from two field sites in central Scotland, a managed grassland and a planted deciduous woodland, with flux measurements of H<span class="inline-formula"><sub>2</sub></span> covering full seasonal cycles. A bespoke flux chamber measurement protocol was developed to deal with the fast decline in headspace concentrations associated with rapid H<span class="inline-formula"><sub>2</sub></span> uptake, in which exponential regression models could be fitted to concentration data over a 7 min enclosure time. We estimate annual H<span class="inline-formula"><sub>2</sub></span> uptake of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">3.1</mn><mo>±</mo><mn mathvariant="normal">0.1</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="52pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="dd5ad2cca7bb1510da350c77dab61691"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-3449-2025-ie00001.svg" width="52pt" height="10pt" src="bg-22-3449-2025-ie00001.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">12.0</mn><mo>±</mo><mn mathvariant="normal">0.4</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="62212690381b940c20daffcfb27b4ec2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-3449-2025-ie00002.svg" width="58pt" height="10pt" src="bg-22-3449-2025-ie00002.png"/></svg:svg></span></span> kg H<span class="inline-formula"><sub>2</sub></span> ha<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span> and mean deposition velocities of <span class="inline-formula">0.012±0.002</span> and <span class="inline-formula">0.088±0.005</span> cm s<span class="inline-formula"><sup>−1</sup></span> for the grassland and woodland sites, respectively. Soil moisture was found to be the primary driver of H<span class="inline-formula"><sub>2</sub></span> uptake at the grassland site, where the high silt/clay content of the soil resulted in anaerobic conditions (near zero H<span class="inline-formula"><sub>2</sub></span> flux) during wet periods of the year. Uptake of H<span class="inline-formula"><sub>2</sub></span> at the forest site was highly variable and did not correlate well with any localised soil properties (soil moisture, temperature, total carbon and nitrogen content). It is likely that the high silt/clay content of the grassland site (55 % silt, 20 % clay) decreased aeration when soils were wet, resulting in poor aeration and low H<span class="inline-formula"><sub>2</sub></span> uptake. The well-drained forest site (60 % sand) was not as restricted by exchange of H<span class="inline-formula"><sub>2</sub></span> between the atmosphere and the soil, showing instead a large variability in H<span class="inline-formula"><sub>2</sub></span> flux that is more likely to be related to heterogeneous factors in the soil that control microbial activity (e.g. labile carbon and microbial densities). The results of this study highlight that there is still much that we do not understand regarding the drivers of H<span class="inline-formula"><sub>2</sub></span> uptake in soils and that further field measurements are required to improve global models.</p> |
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| ISSN: | 1726-4170 1726-4189 |