Trace Element Dynamics in Throughfall of 2 Spruce Forests of French Switzerland, with Low Pollution Levels

1993

S. 445-459

50 Lit. Ang.

Unselbständiges Werk

200041769

Annales des Sciences Forestieres 1993 ; 50,Nr. 5, S. 445-459

The chemical composition of rainfall and throughfall of 2 sites located in very different environments in Switzerland are compared. Calculation of the flux ratios from rainfall and throughfall leads to a differentiation between elements which are highly concentrated when passing though the tree crowns (Mn and Rb), slightly enriched elements (Sr and Ba), elements unaffected by this phenomenom (V, Cr, Ni, Zn and Pb) and element retained by the needles (B and Fe). Analysis of the multielemental chemical structure of solution shows that tree 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 surface. It is therefore difficult to differentiate between dry deposition input and recretion. Nevertheless it is evident that the concentrations of most of the heavy metals are not influenced by dry deposition. This could be due to the low pollution level at these sites. Conversely, Rb enrichment is mainly due to biological cycling and Mn and Ba concentrations are highly modified by this phenomenom. Sr, like Ca, seems to be enriched by 2 different phenomena: dry deposition and recretion. We found some retention of Fe and B on the tree crowns.