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2015
- handle: 10670/1.82896p
- hal: hal-01349106
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Karst Speleothem Organic matter EPR SoilSujets proches
Soil Mould, Vegetable Vegetable mold Earth (Soils) Mold, VegetableCiter ce document
Yves Perrette et al., « Determining soil sources by organic matter EPR fingerprints in twomodern speleothems », Archive Ouverte d'INRAE, ID : 10670/1.82896p
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Résumé
Organic matter (OM) sources and transfers are critical questions at the crossroad of ecology, hydrologyand paleoenvironmental studies in karst environments. Recently chemical or isotopic characterisationsof these organic matters have demonstrated their diversity in karst water and speleothems. However,knowledge of their origin and transfer from soil needs to be improved especially in karst environmentswhere a mosaic of soils occurs. Here we investigate the applicability of the Electron ParamagneticResonance (EPR) signature of OM to seek different soil fingerprints in speleothems. The positions andthe shapes of semiquinone-type radical’s EPR lines are considered as a robust signature of the organicmatter through the different compartment of karst ecosystems. We demonstrate that the combinationof EPR lines simulation constitutes a fingerprint that discriminates folic Leptosol developed on limestoneoutcrops from eutric Cambisols located in the dolines and topographical depressions. We also report theconservation of the thinner OM EPR lines after a water extraction of the organic matter from soils. Finally,OM EPR signatures were detected in two different speleothems sampled near each other: a stalagmiteand a subaqueous flowstone. An unexpected two-orders-of-magnitude discrepancy between the free radicalconcentrations of the subaqueous flowstone and the soils on one hand, and the low free radical concentrationof the stalagmite samples on the other, was ascribed to the kinetics of conformational changesin OM occurring during their transfer through karst either in fast or in slow water pathways. A folicLeptosol fingerprint was found in stalagmite and conversely, an eutric Cambisol fingerprint was foundin the flowstone sample. This unexpected difference between the EPR signatures of the flowstone sampleand stalagmite sample was ascribed to the masking of the Leptosol EPR signature (due to the low concentrationsof free radicals) in the case of the flowstone sample and to the fact that the EPR signature of thestalagmite sample clearly shows the Leptosol is the sole source of the OM. Finally, the folic Leptosolfingerprint remains steady over the last four centuries covered by the stalagmite demonstrating thatthe source of the OM is stable over the growth period strengthening the interest of OM entrapped inspeleothem for paleoenvironment studies.