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Archivages pédologique et dynamiques environnementales : Mise au point d'une nouvelle méthode de reconnaissance des paléovégétations, fondée sur l'analyse spectroscopique dans le proche infrarouge (SPIR) des matières organiques de sols et paléosols

Abstract : Our goal is to develop a new tool to study spatial and temporal dynamics of palaeovegetation. The limits of existing methods to reconstruct past environment of Holocene and Pleistocene at local scale are the starting point of our approach. Our work is to develop a method to study soil memory based on the principles of near infrared spectroscopy (NIRS). NIRS measures the absorbance of a material on the spectral range 1100-2500 nm. The spectrum collected discriminates many components of this material. It provides a "fingerprint" of organic matter. That is why, it has been used for a long time in many industrial sectors. In soil science, it has been mostly used to quantify the soil constituents. In our work, we focus on the nature of soil organic matter that is related to the types of present and past vegetation. Therefore, we test a qualitative approach of combining the spectrum of a soil sample to a type of vegetation. Our approach consists of three stages. The first is to measure the spectrum of organic matter whose origin is known. Thus, we analyze samples of topsoils from sites where the vegetation is known for at least 150 years. A wide range of ecosystems and soil types are represented in a spectral library. The separation between the soils under grassland and under forests is very clear. Finer distinctions between different forest types are also observed. In the second stage, we check the potential of the method on degraded organic matter in complete profiles. The knowledge of palaeovegetation across the millennium is provided by conventional palaeoecological methods. We distinguish the patterns of evolution with high stability of vegetation from the patterns with one or several changes of vegetation. Comparing the spectra of deep horizons with the reference surface horizons enables to reconstruct scenarios that are chronologically calibrated through the contribution of an organic matter turnover model. In the third stage, we examine buried soils. Their spectral signature indicates the nature of the vegetation cover before the burial of the palaeosoil. However, these last results should be considered carefully due to few complementary palaeoecological data. The results reveal a great potential of the NIRS in studies of paleovegetation at local scales. Scenarios of changes proposed for several studied sites confirm the existing results or bring new elements to the study of palaeovegetation in relation to human impact in Alsace during the Holocene. However, in terms of ecosystem and geographical perspective, methodological investigations should continue towards broadening of the reference surface. References of deep horizons and palaeosols should also be consolidated by further palaeoecological studies. This work also opens up opportunities for other applications such as tracing of terrigenous materials in the water flow.
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https://tel.archives-ouvertes.fr/tel-00551528
Contributor : Rosine Schlumberger <>
Submitted on : Tuesday, January 4, 2011 - 8:35:04 AM
Last modification on : Monday, October 19, 2020 - 11:09:25 AM
Long-term archiving on: : Tuesday, April 5, 2011 - 2:43:31 AM

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  • HAL Id : tel-00551528, version 1

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Ertlen Damien. Archivages pédologique et dynamiques environnementales : Mise au point d'une nouvelle méthode de reconnaissance des paléovégétations, fondée sur l'analyse spectroscopique dans le proche infrarouge (SPIR) des matières organiques de sols et paléosols. Sciences de l'Homme et Société. Université Louis Pasteur - Strasbourg I, 2009. Français. ⟨tel-00551528⟩

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