DRY DEPOSITION WASHOFF FROM FOREST TREE LEAVES BY EXPERIMENTAL ACID RAINFALL

Freshly collected leaves from a regenerating forest stand were treated with experimental acid rainfall of pH 4.6 in short-duration laboratory washing trials. The dynamics of initial sulfate and potassium washoff from leaf surfaces were found to be similar between elements and among species. Sulfate and potassium followed negative exponential foliar element washoff curves. Potassium leaching from foliage may occur with dry deposition washoff. The time for completion of the initial element washoff from leaves, in the range of 6-8 min, was similar to previously reported leaf immersion washing times. Potassium was washed from leaf surfaces at a faster rate than was sulfate. Tree species were generally similar for dry deposition washoff amounts and rates within leaching trials. Washoff from lower leaf surfaces was negligible. The washoff curve analysis presented in this study appears to produce an accurate estimate of previous dry deposition to leaf surfaces, and eliminates many of the problems and limitations associated with bulk leaf washing immersion approaches.