Characterization and migration of atmospheric REE in soils and surface waters.
Dominique AUBERT*, Peter STILLE*, Anne PROBST**, François GAUTHIER-LAFAYE*, Laurent POURCELOT***, and Mireille DEL NERO****
Geochimica et Cosmochimica Acta, Vol. 66, No. 19, pp. 3339-3350
Rainwater and snow collected from three different sites in France (Vosges Mountains, French Alps and Strasbourg) show more or less similar shapes of their REE distribution patterns. Rainwater from Strasbourg is the most REE enriched sample, whereas precipitations from the two mountainous, less polluted catchments are less REE enriched and have concentrations close to seawater. They are all strongly LREE depleted.
Different water samples from an Alpine watershed comprising snow, interstitial, puddle and streamwater show similar REE distributions with LREE enrichment (rainwater normalized) but MREE and HREE depletion. In this environment, where water transfer from the soil to the river is very quick due to the low thickness of the soils, it appears that REE in streamwater mainly originate from atmospheric inputs. Different is the behaviour of the REE in the spring- and streamwaters from the Vosges Mountains. These waters of long residence time in the deep soil horizons react with soil and bedrock REE carrying minerals and show especially significant negative Eu anomalies compared to atmospheric inputs. Their Sr and Nd isotopic data suggest that most of the Sr and Nd originate from apatite leaching or dissolution. Soil solutions and soil leachates from the upper soil horizons due to alteration processes strongly depleted in REE carrying minerals, have REE distribution patterns close to those of lichens and throughfall. Throughfall is slightly more enriched especially in light REE than filtered rainwater probably due to leaching of atmospheric particles deposited on the foliage and also to leaf excretion.
Data suggest that Sr and Nd isotopes of the soil solutions in the upper soil horizons originate from two different sources: 1) An atmospheric source with fertilizer, dust and seawater components and 2) A source mainly determined by mineral dissolution in the soil. These two different sources are also recognizable in the Sr and Nd isotopic composition of the tree's throughfall solution. The atmospheric contributions of Sr and Nd to throughfall and soil solution are of 20 to 70 and 20%, respectively. In springwater, however, the atmospheric Sr and REE contribution is not detectable.
* Ecole et Observatoire des Sciences de la Terre (EOST), ULP/CNRS, UMR 7517, Centre de Géochimie de la Surface, 1 rue Blessig, 67084 Strasbourg Cedex, France
** Laboratoire des Mécanismes de Transferts en Géologie (LMTG), UPS/CNRS, UMR 5563, 38 rue des 36 Ponts, 31400 Toulouse, France
*** Institut de Radioprotection et de Sûreté Nucléaire IRSN, CEA Cadarache Bât 153, 13108 St Paul-lez-Durance, France
**** Institut de recherches subatomiques, CNRS/IN2P3, 23 rue du Loess,67037 Strasbourg Cedex, France