Precipitation chemistry at a high elevation forest in central Taiwan

Abstract

High elevation ecosystems are particularly sensitive to environmental change. Mountain agriculture is extending to areas at high elevations in Taiwan but the effects on nutrient cycling of the surrounding ecosystems are largely unknown. We examined precipitation chemistry at Piluchi Experimental Forest in central Taiwan to evaluate the contributions of local air pollution and long-range transport of air pollutants on nutrient cycling at this seemingly remote forest. Sea-salt aerosols and anthropogenic pollutants resulting from long-range transport of air pollutants and mountain agriculture activities are the key factors affecting precipitation chemistry at Piluchi Experimental Forest. Precipitation chemistry was dominated by ions of oceanic origin in the summer and by anthropogenic pollutants SO₄²⁻, NO₃⁻ and NH₄⁺ in the winter and spring, the northeast monsoon season. The much higher concentrations of S and N in the northeast monsoon season than the summer suggest a substantial contribution from long-range transport as the prevailing air masses moved from inland China and passed over the industrialized east coast of China before arriving in Taiwan. The very high concentration of NH₄⁺ (22 μeq L⁻¹) in the spring, when the local application of N-containing fertilizers was high, signifies the influences of mountain agriculture. Despite very low concentrations relative to other sites in Taiwan, annual input of NH₄⁺ (3.6 kg ha⁻¹ year⁻¹), NO₃⁻ (7.2 kg ha⁻¹ year⁻¹) and SO₄²⁻ (10 kg ha⁻¹ year⁻¹) via precipitation was substantial suggesting that high elevation ecosystems of Taiwan are not free from the threat of atmospheric deposition of pollutants.

Keywords:

• High elevation agriculture
• Long-range transport
• Monsoon season
• Nitrogen fertilizer
• Precipitation chemistry

Acknowledgments

The study was supported in part by National Science Council (NSC94-2815-C-018-014-B) and Archilife Research Foundation. We thank Matt Vadeboncoeur and Dr. Joshua West for insightful comments on previous versions of the manuscript.