| Summary: | 碩士 === 國立東華大學 === 自然資源管理研究所 === 92 === The fog deposition flux at the Yuanyang Lake (YYL) site was estimated in this study by a micrometeorological model first developed by Lovett (1984). The YYL site is located in northeastern Taiwan at an altitude of 1670 m a.s.l. and subjected to strong influences by fog. The stand of the site is a plantation of Chamaecyparis obtusa var. formosana with even age and homogeneous canopy structure. For calculating the fog deposition flux at this site, the vegetation parameters relating to to the canopy structure, as well as the meteorological parameters relating to wind speed and fog water concentration were determined. The most important vegetation parameter, the vertical distribution of the surface area index, of the stand was investigated for C. obtusa var. formosana. The surface areas of leaves, twigs, and stem were measuerd using 11 sample trees and extrapolated to stand scale using a series of allometric equations. The wind speed and visibility data were taken from the long-term monitoring records from the meteorological tower beside the stand. The other parameters relating to aerodynamic resistances and boundary layer resistances were adoped from the measurements/parameterization at a Norway spruce site in Germany (Scheer, 2002).
Total surface area index at the YYL site was 14.6 m2 m-2 including all sides of branch surface area, leaf surface area and stem surface area. The leaf area index of the site was 12.6 m2 m-2, which comprised 86% of the total surface area index. Liquid water content was calculated from visibility. Droplet size distribution was calculated from two distribution model. One was Best (1951) distribution model, and another was the log_normal distribution model modified by Sheer (2002) to describe the distribution at Waldstein site. Although the deposition flux predicted by Best model was higher than that from log_normal model, the prediction of the droplet distribution was very similar. Due to the recalculation of liquid water content and droplet size distribution, the uncertainty and errors would become very large and unmeasured.
The annual fog deposition flux at the YYL site was calculated for the period from March 2003 to February 2004 and the resulting deposition flux was 313mm yr-1. It was about 10% of total atmospheric water deposition, and similar to the value that was estimated by experimental method (328mm). Due to the higher ion concentrations of fog water than those of the rain water, the ions deposited through fog had very high proportions in total atmospheric deposition, especially for H+ (62%), Cl-(35%), SO42-(39%), nitrogen in NH4+(60%), nitrogen in NO3-(54%), total nitrogen(58%),and dissolved organic nitrogen(47%). It indicated that the fog deposition flux plays an important role in atmospheric nutrients and pollutants input at the YYL site.
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