Dry deposition and canopy exchange in a mixed oak forest as determined by analysis of throughfall.
Multiple regression analysis was applied to single-event samples of throughfall beneath oak trees to separate the contributions of dry deposition and canopy exchange to the net deposition (throughfall minus precipitation). Results for chestnut oak (Quercus prinus) in the growing season indicate that 62 and 42% of the net deposition of SO42- and Ca2+, respectively, were supplied by canopy exchange, with the remainder being washed-off dry deposition. For white oak (Quercus alba), the corresponding values were 81 and 73%. Dry deposition accounted for 30 and 71% of the total atmospheric input of SO42- and Ca2+, respectively. For nitrate, dry deposition was at least 30% of the total atmospheric input, but some uptake of both wet and dry deposition probably occurred in the canopy. For potassium, much of the measured dry deposition appeared to be particulate material released and redeposited within the canopy. Wet deposition dominated the throughfall flux of sulphate and nitrate, but dry deposition dominated that for Ca2+ and canopy exchange dominated that for K+.