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ENVIRONMENTAL ISSUES

Fog and Precipitation Chemistry at a Mid-land Forest in Central Taiwan

^a National Fengshan Vocational High School, No. 51, Wenheng Rd., Fengshan City, Kaoshiung County, 83052, Taiwan
^b Dep. of Life Science, National Taiwan Normal Univ., No. 88 Ting-Chow Rd., Section 4, Taipei, 11677, Taiwan
^c Taiwan Forestry Research Institute, No. 53 Nan-Hai Rd., Taipei 10066, Taiwan
^d Dep. of Atmospheric Science, National Central Univ., No. 300, Jhongda Rd., Jhongli City, Taoyuan 32001, Taiwan

^* Corresponding author (tclin{at}ntnu.edu.tw).

Received for publication August 2, 2007. ABSTRACT

We analyzed fog and bulk precipitation chemistry at a cloud forest in central Taiwan where mountain agriculture activities are highest. There were 320 foggy days (visibility <1000 m) recorded between April 2005 and March 2006. Fog was most frequent between April 2005 and July 2005 and in March 2006 (153/153 d) and least frequent in January 2006 (21/31 d). The total fog duration was 2415 h, representing 28% of the sampling period. Compared with bulk precipitation, fog was disproportionally enriched in NO₃^– and SO₄^2– relative to K⁺, Ca²⁺, Mg²⁺, and NH₄⁺, resulting in higher a content of nitric acid and sulfuric acid than weak acids or neutral salts and, therefore, higher acidity (median pH, 4.9) in fog than in bulk precipitation (median and mean pH, 5.5). The very high input of NH₄⁺ (47 kg N ha^–1 yr^–1) through bulk precipitation suggests that the use of fertilizer (ammonium sulfate and animal manure) associated with mountain agriculture has a major impact on atmospheric deposition at the surrounding forest ecosystems. The input of inorganic N reached 125 kg N ha^–1 yr^–1 and likely exceeded the biological demand of the forest ecosystem. Sulfate is the most abundant anion in fog at Chi-tou and in precipitation at various forests throughout Taiwan, suggesting that the emission and transport of large quantities of SO_2, the precursor of SO₄^2–, is an island-wide environmental issue.

Abbreviations: CC, calculated conductivity • CPD, conductivity percentage difference • MC, measured conductivity