Throughfall patterns in a subtropical rain forest of northeastern Taiwan

Throughfall chemistry of a subtropical rain forest in Taiwan was examined f or 3 yr to understand patterns of nutrient inputs to the forests of this re gion. Annual throughfall fluxes for NH4+, NO3-, and SO42- (89, 28, and 83 m mol/m(2)/yr, respectively) were close to the levels of the most polluted ar eas in the temperate region. The lack of major emission sources near the st udy site indicates that most of the pollutants were regional and/or interna tional in origin. High rates of cation leaching from the forest canopy were evident and the pattern is similar to that seen in heavily polluted temper ate forests. Typhoons played a central role in the hydrology of the study f orest with eight typhoons contributing 26% of the total rainfall in 320 h o ver the three years monitored. This typhoon input represented 20% of the to tal precipitation flux of the ions found in seasalt aerosols but less than 10% of anthropogenically enriched ions. Canopy leaching was an important so urce of base cations in throughfall and NO; was retained in the canopy, Usi ng the Na-ratio method the contribution of dry deposition relative to preci pitation input was estimated to be 40% in the summer and 10% in the winter, The contribution of dry deposition to total deposition is small relative t o many temperate forests and might result from the lack of long dry periods between precipitation events. Net throughfall flux was negatively related to precipitation concentration for H+, NH4+, NO3-, and SO42-, suggesting th at passive movement was important in characterizing throughfall dynamics.