Previous studies on waters of a streamlet in the Vosges Mountains (Eastern France) have shown that strontium and rare earth elements (REE) mainly originate from preferential dissolution of apatite during weathering. However, stream water REE patterns normalized to apatite are still depleted in the light REE (LREE, La-Sm) pointing to the presence of an additional LREE depleting process. Vegetation samples are strongly enriched in LREE compared to stream water and their Sr and Nd isotopic compositions are comparable with those of apatite and stream water. Thus, the preferential LREE uptake by vegetation might lead to an additional LREE depletion of surface runoff in the forested catchment. Mass balance calculations indicate, that the yearly LREE uptake by vegetation is comparable with the LREE export by the streamlet and, therefore, might be an important factor controlling LREE depletion in river water. This is underlined by the observation that rivers from arctic and boreal regions with sparse vegetation appear to be less depleted in LREE than rivers from tropical environments or boreal environments with a dense vegetation cover.
a- CGS, CNRS, UMR 7517, F-67084 Strasbourg, France
b- EA 2642 Géosciences, Université de Franche-Comté, F-25030 Besançon, France
c- Institut de Radioprotection et de Sûreté Nucléaire IRSN, Cadarache, F-13108 St. Paul Lez Durance, France
d- Inst. Géol., Université de Neuchâtel, CH-2007 Neuchâtel, Switzerland
e- CEFREM, UMR 5110, Université de Perpignan, F-66860 Perpignan, France