Precipitation chemistry at the Lienhuachi Experimental Forest in central Taiwan

Abstract

This paper examines weekly wet-only precipitation chemistry in the Lienhuachi Experimental Forest between October 2004 and September 2005. The volume-weighted mean annual pH was 4.84, lower than the Taiwan Environmental Protection Adminstration's criterion for acid rain (pH＜5.0). It was also lower than the value measured 13 years ago at the same site (5.51), despite decreases in the emissions of acidic pollutants over the same period of time. Coincident decreases in the emission of particulate pollutants with high concentrations of acid-neutralizing base cations, as well as differences in the collection methods (wet-only versus bulk precipitation) are possible explanations for the observed differences in precipitation pH. Seasonally, pH was lower in spring and winter than in summer and fall. This pattern is in agreement with many other studies throughout Taiwan and is often attributed to the high contribution of pollutants transported from China in the winter and spring. The rates of S and inorganic N deposition, of 11.5 and 13.8 kg ha-1 yr-1, respectively, were higher than those in the northeastern US where high acid deposition is a major concern in forest nutrient cycling and health. The impacts of such high acidic deposition on forest ecosystems need to be thoroughly examined. The rate of S deposition observed in the Lienhuachi Experimental Forest is similar to those of several other forest ecosystems in central Taiwan, whereas the rate of N deposition at the Lienhuachi Experimental Forest is considerably higher. It appears that areas of high N deposition are more localized than those of S deposition. The application of commercial fertilizers around the Lienhuachi Experimental Forest may explain the observed higher N deposition at our study site compared to other forest ecosystems in central Taiwan.