Acid fog damage of beech at Hinokiboramaru-Tanzawa, Japan.

Decline of Japanese beech forest has been obvious at the Tanzawa Mountains near Tokyo. Observations on fog, precipitation and stem flow were performed during June-October, 1994 on both, NE (with healthy beech) and S-SE (with unhealthy beech) slopes, collecting samples biweekly. Chemical species were determined by ion-chromatography and pH meter. The results show that the pH of the precipitation was between 4.4-5.2, with no clear differences in the concentrations of chemical species between both sites and seasons. The pH of the fog water was high from May to the middle of August and lower from mid-August to October at both sites. The concentrations of most chemical species were higher in fog samples than precipitation samples. The concentrations of potassium and magnesium ions in the stem flow of an unhealthy tree on the S-SE slope were higher than those on the NE slope. In June-October, 1995, ten pairs of event fog water samples were obtained with indicating that the pH was below 4.0 for five pairs of event fog water samples. Lower pH value was obtained on the S-SE slope than on the NE slope in every event. Concentrations of most chemical species were always higher in the fog samples from the S-SE slope than those from the NE slope. The equivalent ratio of NO3-/nssSO4(2-) was higher in the fogs of higher acidity. From the result of atmospheric current analysis using a model, it was suggested that the polluted air over the Tokyo Metropolitan Area affected the fog acidity directly and also indirectly, according to the pressure patterns.