3,5,2,4- 1Université Paris-Saclay, UMR8148 GEOPS, Orsay, France (cecile.quantin@universite-paris-saclay.fr)
- 2Institut de Recherche pour le Developpement (IRD), Noumea, New Caledonia
- 3Service Geologique de Nouvelle-Caledonie (SGNC), Noumea, New Caledonia
- 4Institut de Mineralogie, de Physique des Materiaux et de Cosmochimie (IMPMC), Sorbonne Universite, UMR CNRS 7590, MNHN, EMR IRD 206, Paris, France
- 5Université de Lorraine, CNRS, LIEC, F-54000 Nancy, France
- 6European Synchrotron Radiation Facility (ESRF), The European Synchrotron, Grenoble, France
- 7Observatoire des Sciences de l’Univers de Grenoble (OSUG), Université Grenoble-Alpes, CNRS, Grenoble, France
- 8HydroSciences Montpellier, Universite de Montpellier, UMR 050, Montpellier, France
Fire is increasingly recognized as a significant driver of trace metal mobility, posing risks to water quality, especially in metal-rich environments such as ultramafic wetlands. In such environments, wildfires can trigger the formation of Acid Sulfate Soils (ASS), further amplifying metal release [1]. This study investigates the geochemical processes controlling nickel (Ni) dynamics in such contexts, focusing on a burned doline and its downstream drinking water catchment on Île des Pins, New Caledonia.
Water chemistry analysis and advanced imaging techniques (SEM, TEM, XAS) reveal extreme post-fire dissolved Ni concentrations (up to 368,000 µg/L in the doline and 4,300 µg/L downstream), and transformation of the studied Gleysols into ASS. Those observations are interpreted as resulting from a multi-step reaction sequence: (1) oxidation of Ni-bearing pyrite and millerite due to increased oxygen diffusion, (2) acidification from sulfide oxidation, and (3) acidic dissolution of Ni-bearing chrysotile. This cascade scenario leads to the release of nickel, magnesium, and sulfate, which then precipitate as Ni-hexahydrite [(NixMg1-x)SO4.6H2O)] upon water evaporation.
Ni-hexahydrite, which is a highly soluble compound, accounts for 40–50% of the solid nickel in surface soils and drives the nickel dynamics at the soil-water interface and at catchment scale through repeated precipitation/dissolution cycles. These findings show that wildfires in ultramafic wetlands can severely mobilize trace metals via ASS formation, with metal-sulfates playing a crucial role in post-fire geochemical cycling.
[1] Thery G., Quantin C., Calmels D., Jeanpert J., Morin G., Montargès-Pelletier E., Bourbon E., Kessie M., Kieffer I., Genthon P., Juillot F., 2025. Nickel dynamics in acid sulfate soils formed after wildfires across ultramafic wetlands of New Caledonia: the key role of Ni-hexahydrite. Journal Soils and Sediments, doi.org/10.1007/s11368-025-04190-9
How to cite: Quantin, C., Thery, G., Calmels, D., Jeanpert, J., Morin, G., Montargès-Pelletier, E., Bourbon, E., Kessié, M., Kieffer, I., Genthon, P., and Juillot, F.: Post-fire nickel mobility in acid sulfate soils developed in ultramafic wetlands of New Caledonia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7236, https://doi.org/10.5194/egusphere-egu26-7236, 2026.
