ATMOSPHERIC DEPOSITION AND CANOPY INTERACTIONS FOR CONIFER AND DECIDUOUS FORESTS IN NORTHERN SPAIN

The effect of forest canopy on the chemical composition of throughfall was studied in four forests, two coniferous plantations of Pinus radi ata and two deciduous forests (Quercus robur and e. rubra, respectivel y) near Bilbao (Bizkaia), Basque Country (Northern Spain) during one y ear. The study areas are assumed to have different levels of pollution : Manzanal suffers industrial pollution mainly of SO42- and N.NO3-, wh ile Durango has industrial and agricultural pollution mainly of N.NH4 and SO42-. The study presents data on bulk precipitation and throughf all, and on the quantities of inorganic N (N.NH4+ + N.NO3-), SO42-, Ca 2+, Mg2+, Na+, K+ and Cl- reaching the forest floor. The nutrient inpu t to the forest floor differed within the four studied sites. The capa city of neutralization of the deposition was better on deciduous fores t than on the coniferous. Leaching in association with the canopy wash off were the most significant sources of base cations in deciduous and coniferous throughfall. Despite the pollution levels in Manzanal and Durango no effect on tree leaves were observed during the study period .