Fire as a Removal Mechanism of Pyrogenic Carbon From the Environment: Effects of Fire and Pyrogenic Carbon Characteristics
Pyrogenic carbon (PyC, charcoal) is produced during vegetation fires at a rate of ~116–385 Tg C yr−1 globally. It represents one of the most degradation-resistant organic carbon pools, but its long-term fate and the processes leading to its degradation remain subject of debate. A frequently highligh...
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Frontiers Media S.A.
2018-10-01
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| Series: | Frontiers in Earth Science |
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| Online Access: | https://www.frontiersin.org/article/10.3389/feart.2018.00127/full |
| _version_ | 1818538686706352128 |
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| author | Stefan H. Doerr Cristina Santín Cristina Santín Agustín Merino Claire M. Belcher Greg Baxter |
| author_facet | Stefan H. Doerr Cristina Santín Cristina Santín Agustín Merino Claire M. Belcher Greg Baxter |
| author_sort | Stefan H. Doerr |
| collection | DOAJ |
| description | Pyrogenic carbon (PyC, charcoal) is produced during vegetation fires at a rate of ~116–385 Tg C yr−1 globally. It represents one of the most degradation-resistant organic carbon pools, but its long-term fate and the processes leading to its degradation remain subject of debate. A frequently highlighted potential loss mechanism of PyC is its consumption in subsequent fires. However, only three studies to date have tested this hypothesis with reported losses of <8–37%, with the effects of PyC chemical characteristics and fire conditions on PyC loss in wildfires remaining unexplored. To address this, we placed materials with different degrees of thermal and chemical recalcitrance (A: wildfire charcoal, B: slash-pile charcoal, C: pine wood and D: cedar wood) on the ground surface just prior to a high-intensity and a low-intensity boreal forest wildfire. Mass losses were highly variable and dependent on fire- and sample characteristics. Mass losses across both fires (as % of dry weight) were for A: 66.5 ± 25.2, B: 41.7 ± 27.2, C: 78.2 ± 14.9, and D: 83.8 ± 18.9. Mass loss correlated significantly with maximum temperature (Tmax) recorded on sample surfaces (r = 0.65, p = 0.01), but only weakly (r = 0.33) with time >300°C. Mass losses also showed a significant negative correlation (r = −0.38, p = 0.05) with thermal recalcitrance (T50) determined using Differential Scanning Calorimetry (DSC) and Tmax with charcoal reflectance (Ro) determined after the fires (r = 0.46, p = 0.05). Losses in the high-intensity fire were significantly higher (p = 0.05) than in the low-intensity fire, but the latter had a higher rate of conversion of fuel to PyC. Our results demonstrate that exposure to fire can indeed be a significant removal mechanism for PyC that remains exposed on the ground after a previous fire. The losses found, however, are likely to represent an extreme upper range as most PyC produced in a fire would not remain exposed on the ground surface by the time the next fire occurs. Our data also demonstrate, for real wildfire conditions, the (i) contrasting resistance of different PyC types to combustion and (ii) contrasting net PyC losses between different fire intensities. The DSC and reflectance (Ro) results support the usefulness of these analyses in reflecting thermal degradation resistance and temperature exposure under actual wildfire conditions. |
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| publishDate | 2018-10-01 |
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| spelling | doaj.art-673e0ea1e53f4c8796001bf5be850b4b2022-12-22T00:50:07ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632018-10-01610.3389/feart.2018.00127342027Fire as a Removal Mechanism of Pyrogenic Carbon From the Environment: Effects of Fire and Pyrogenic Carbon CharacteristicsStefan H. Doerr0Cristina Santín1Cristina Santín2Agustín Merino3Claire M. Belcher4Greg Baxter5Department of Geography, College of Science, Swansea University, Swansea, United KingdomDepartment of Geography, College of Science, Swansea University, Swansea, United KingdomDepartment of Biosciences, College of Science, Swansea University, Swansea, United KingdomDepartment of Soil Science and Agricultural Chemistry, University of Santiago de Compostela, Lugo, SpainWildfire Lab, Hatherly Laboratories, University of Exeter, Exeter, United KingdomWildfire Operations Research, FPInnovations, Hinton, AB, CanadaPyrogenic carbon (PyC, charcoal) is produced during vegetation fires at a rate of ~116–385 Tg C yr−1 globally. It represents one of the most degradation-resistant organic carbon pools, but its long-term fate and the processes leading to its degradation remain subject of debate. A frequently highlighted potential loss mechanism of PyC is its consumption in subsequent fires. However, only three studies to date have tested this hypothesis with reported losses of <8–37%, with the effects of PyC chemical characteristics and fire conditions on PyC loss in wildfires remaining unexplored. To address this, we placed materials with different degrees of thermal and chemical recalcitrance (A: wildfire charcoal, B: slash-pile charcoal, C: pine wood and D: cedar wood) on the ground surface just prior to a high-intensity and a low-intensity boreal forest wildfire. Mass losses were highly variable and dependent on fire- and sample characteristics. Mass losses across both fires (as % of dry weight) were for A: 66.5 ± 25.2, B: 41.7 ± 27.2, C: 78.2 ± 14.9, and D: 83.8 ± 18.9. Mass loss correlated significantly with maximum temperature (Tmax) recorded on sample surfaces (r = 0.65, p = 0.01), but only weakly (r = 0.33) with time >300°C. Mass losses also showed a significant negative correlation (r = −0.38, p = 0.05) with thermal recalcitrance (T50) determined using Differential Scanning Calorimetry (DSC) and Tmax with charcoal reflectance (Ro) determined after the fires (r = 0.46, p = 0.05). Losses in the high-intensity fire were significantly higher (p = 0.05) than in the low-intensity fire, but the latter had a higher rate of conversion of fuel to PyC. Our results demonstrate that exposure to fire can indeed be a significant removal mechanism for PyC that remains exposed on the ground after a previous fire. The losses found, however, are likely to represent an extreme upper range as most PyC produced in a fire would not remain exposed on the ground surface by the time the next fire occurs. Our data also demonstrate, for real wildfire conditions, the (i) contrasting resistance of different PyC types to combustion and (ii) contrasting net PyC losses between different fire intensities. The DSC and reflectance (Ro) results support the usefulness of these analyses in reflecting thermal degradation resistance and temperature exposure under actual wildfire conditions.https://www.frontiersin.org/article/10.3389/feart.2018.00127/fullblack carbonboreal forestcarbon balancecharcoalcharcoal reflectancewildfire |
| spellingShingle | Stefan H. Doerr Cristina Santín Cristina Santín Agustín Merino Claire M. Belcher Greg Baxter Fire as a Removal Mechanism of Pyrogenic Carbon From the Environment: Effects of Fire and Pyrogenic Carbon Characteristics Frontiers in Earth Science black carbon boreal forest carbon balance charcoal charcoal reflectance wildfire |
| title | Fire as a Removal Mechanism of Pyrogenic Carbon From the Environment: Effects of Fire and Pyrogenic Carbon Characteristics |
| title_full | Fire as a Removal Mechanism of Pyrogenic Carbon From the Environment: Effects of Fire and Pyrogenic Carbon Characteristics |
| title_fullStr | Fire as a Removal Mechanism of Pyrogenic Carbon From the Environment: Effects of Fire and Pyrogenic Carbon Characteristics |
| title_full_unstemmed | Fire as a Removal Mechanism of Pyrogenic Carbon From the Environment: Effects of Fire and Pyrogenic Carbon Characteristics |
| title_short | Fire as a Removal Mechanism of Pyrogenic Carbon From the Environment: Effects of Fire and Pyrogenic Carbon Characteristics |
| title_sort | fire as a removal mechanism of pyrogenic carbon from the environment effects of fire and pyrogenic carbon characteristics |
| topic | black carbon boreal forest carbon balance charcoal charcoal reflectance wildfire |
| url | https://www.frontiersin.org/article/10.3389/feart.2018.00127/full |
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