TRACE-ELEMENT DYNAMICS IN THROUGHFALL OF 2 SPRUCE FORESTS OF FRENCH SWITZERLAND, WITH LOW POLLUTION LEVELS

Trace element dynamics In throughfall of 2 spruce forests of French Sw itzerland, with low pollution levels. The chemical composition of rain fall and throughfall of 2 sites located in very different environments in Switzerland are compared. Calculation of the flux ratios from rain fall and throughfall leads to a differentiation between elements which are highly concentrated when passing though the tree crowns (Mn and R b), slightly enriched elements (Sr and Ba), elements unaffected by thi s phenomenom (V, Cr, Ni, Zn and Pb) and element retained by the needle s (B and Fe). Analysis of the multielemental chemical structure of sol ution shows that free crown induces clear correlations between element concentrations. This effect is attributed to the input of acidifying anions and to the existence of a chemical equilibrium on the needle su rface. If is therefore difficult to differentiate between dry depositi on input and recretion. Nevertheless it is evident that the concentrat ions of most of the heavy metals are not influenced by dry deposition. This could be due to the tow pollution level at these sites. Converse ly, Rb enrichment is mainly due to biological cycling and Mn and Ba co ncentrations are highly modified by this phenomenom. Sr, like Ca, seem s to be enriched by 2 different phenomena: dry deposition and recretio n. We found some retention of Fe and B on the tree crowns.