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Pedogenesis and phosphorus species evolution : reconstruction from mountain lake sediment archives
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Edité par CCSD -
Edytem équipe Archives Continentales 2011-2015. International audience. Phosphorus (P) plays an important role for the development of lake ecosystems. In particular, lake productivity is strongly linked to the nutrient bioavailability, which depends on P species. The natural dynamic of this nutrient is largely controlled by soil cover evolution. The study of P species modifications in relation with soil development is thus a key to better understand lake ecosystem evolution. Lakes act as natural traps of erosion products, lake sediments represent thus potentially interesting archives of past soil history. The sediment record of Lake Anterne (2063 m asl, North French Alps) covering the last ~10 000 years has proved, in a previous study, its capacity to record soil cover changes. To tackle our question, samples corresponding to different steps of soil development were thus chosen for P speciation analyses. Furthermore, a soil sequence, taken from the catchment, was analysed to better constrain our interpretations of the lacustrine archive. Synchrotron techniques (P K-edge XANES and XRF mapping) were applied on lake sediments, soils and references (mineral and organic) to distinguish between the different P species. Results show that soil development raises the P species diversity. At the onset of the Holocene, when rocks and leptosols dominated the catchment cover, P was under form of apatite. Then, the pedogenesis triggered the dissolution of apatite and the formation of phosphate adsorbed on Fe and Al oxides and on Fe, Al-organic-complexes. These species suggest also that soils were dominated by podzols.
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