HR: 1340h
AN: V23A-1240    [Abstracts]
TI: Use of B Isotopes to Investigate the Influence of the Vegetation on the Rate of Soil Weathering
AU: * Lemarchand, D
EM: lemarcha@illite.u-strasbg.fr
AF: Centre de Geochimie de la Surface, 1 rue Blessig, Strasbourg, 67000, France
AU: Cividini, D
EM: damien.cividini@illite.u-strasbg.fr
AF: Centre de Geochimie de la Surface, 1 rue Blessig, Strasbourg, 67000, France
AU: Chabaux, F
EM: fchabaux@illite.u-strasbg.fr
AF: Centre de Geochimie de la Surface, 1 rue Blessig, Strasbourg, 67000, France
AB: The rate at which soil minerals are weathered and the influence of the vegetal cover on the intensity and the nature of the reactions that release solutes from parent rocks to natural waters are still poorly understood. A way to investigate interactions between soil weathering and plant development is to focus on geochemical tools that are distinctively affected by these two processes and to monitor their behavior along yearly time scales, relevant to the soil/plant system. According to this approach, boron isotopes are particularly interesting because they undergo great isotopic fractionation during water/rock interactions and they are micro-nutrients essential for the life development. To monitor seasonal variations of the B fluxes in the soil/plant system, we benefit from the equipped experimental Strengbach catchment (Vosges, France) where vegetation samples, rainfalls, throughfalls, soil solutions at various depths (5, 10, 30, 60 cm) and spring waters are collected every 6 weeks from 2003 up to now. The observed B fluxes at the watershed scale reveal that it is controlled by the vegetation cycling because the amount of B involved in the vegetation cycling if about 5 times greater that its discharge at the outlet of the basin. Analyses of the B isotopic compositions of vegetation samples and throughfalls reveal unexpected isotopic fractionation that makes the vegetation-related B fluxes quit distinguishable from those controlled by water/rock interactions. The fact that the B geochemical cycle is regulated by the vegetation cycle together with an easy-to- follow isotopic signature makes then possible to determine the relative part of the vegetal activity from the soil weathering rate. We developed a 1D model of the B bio-geochemical cycle at the soil/plant scale that takes into account the transient features of the vegetation cycling and the water transport in soil. The results of the model reveal distinct reaction zones in soils according to its mineralogy and the ratio between the intensities of the vegetal activity and mineral weathering. This approach makes then possible to calculate the rate at which B is released from soil minerals and offer the opportunity to go further in the characterization of the controls and feedbacks that regulate interactions between soil and plant.
UR: http://ohge.u-strasbg.fr/indexuk.html
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1030 Geochemical cycles (0330)
DE: 1039 Alteration and weathering processes (3617)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting