THE EFFECTS OF SO2 AND O-3 FUMIGATION ON ACID DEPOSITION AND FOLIAR LEACHING IN THE LIPHOOK FOREST FUMIGATION EXPERIMENT

The ambient pollution climate at the Liphook forest fumigation site, where coniferous trees were fumigated with SO2 and O-3 for 4 years under field conditions, was characteristic of the fringes of the areas where pollutant effects are a problem. Experimental treatments increased SO2 concentrations to levels more characteristic of Eastern Europe, and summer O-3 concentrations by 30%. Deposition of SO2 to the soil between the trees (inferred from shallow lysimeters) was significant, the deposition velocity being 2.1 mm s(-1). Deposition to Scots pine and Sitka spruce canopies was greater, deposition velocities being 8.5 and 9.4 mm s(-1), respectively. These high values may perhaps be explained by co-deposition with NH3. Calculations assume that dry deposition was the sole source of SO42- gain in throughall, and that there was no significant retention by the trees. There was a trend for O-3 to enhance SO2 deposition to both soil and trees. Fumigation with SO2 led to a significant increase in leaching of cations from foliage. Each species neutralized about 63% of the dry-deposited SO2, predominantly by ion exchange for Ca and K. Equations are provided which allow calculation of foliar leaching given SO2 concentrations or SO42- deposition. Fumigation increased the rate of nutrient cycling considerably, without affecting foliar concentrations or damaging the trees. Ozone treatments did not enhance foliar leaching, calling into question some suggested mechanisms for the causes of forest decline.