攔截沉降(Occult deposition)是大氣沉降物經由雲霧進入營養循環的沉降型態。此形式進入生態系水量雖相對雨水少，但因雲霧一般形成於 污染物濃度較高的近地表處，而且霧滴的顆粒粒徑較小導致霧水攔截 物質的總表面積遠高於相同體積的雨水，使得霧水中污染物濃度通常 較雨水高，物質透過雲霧進入生態系統的量亦可能相當可觀。臺灣的雲 霧林帶是茶葉的重要產區，除降雨外，雲霧也是營養輸入的重要途徑， 為因應全球茶葉需求增加，大量施用含氮肥料、茶園面積擴張均可能直 接或間接影響生態系統營養收支的平衡。本研究於台灣北部地區的一 處茶園收集並分析雨水、霧水、穿落水、溪水，以評估山區農業生態系 統營養收支的情形。離子在雨水中的濃度由高到低依序為 Cl- > Na+ > SO42- > K+ > NO3- > NH4+ > Ca2+ > Mg2+，在霧水中則為 Na+ > Cl- > NO3- > Mg2+ > SO42- > Ca2+ > NH4+ > K+。由於研究茶園靠近台灣東北海岸， Cl-、Na+是雨霧水中相對豐富度最高的離子，顯示海洋飛沫是影響雨霧 水化學的重要因素。所有離子和有機氮在霧水中的濃度均明顯高於雨水，而離子濃度比率(fog : precipitation)由小到大依序為 K+ (2.11) < NH4+ (5.59) < SO42- (6.99) < Ca2+ (9.25) < Cl- (9.26) < NO3- (10.3) < Na+ (14.2) < Mg2+ (22.2) < DON (46.9)，介於有主要污染來源 (多大於 10)和沒有污染來源 (小於 5)的地區間，可能和茶園鄰近大台北地區但周圍主要被森林覆蓋有關。主成分分析結果指出農業活動是造成霧水 K+、NH4+濃 度變異的主要原因，表明霧水化學更容易因局部地區排放而改變。Ca2+、 Mg2+在穿落水中含量較高，應是來自雨水與茶樹樹冠的淋溶作用，且 雨水中多數離子的濃度和淨穿落量的負向關係顯示濃度梯度差可能是 造成雨水與茶樹樹冠交換的重要機制。

Occult deposition is deposition of pollutants by direct contact with mist or cloud. The total quantity of fog water is in general much less than that of rain water, however, concentrations in cloud water could be very high. This is because the formation of fog is close to the ground where concentration of air pollutants is high and the per unit volume surface of fog is much higher than that of rain. Due to higher concentrations, the contribution of chemical deposition from fog often exceeds its contribution on water input and its effects on ecosystem cannot be neglected. Cloud forest in Taiwan is also important for tea plantation. In addition to precipitation, fog is another important pathway of atmospheric deposition in tea plantations. As global tea consumption is increasing, tea plantations are expanding and more nitrogen fertilizers are used to increase yields, which could directly or indirectly influence ecosystems. Through collection and analyses of rainfall, fog, throughfall, and stream water, this study aims to evaluate the impacts of atmospheric deposition on nutrient input-output of tea plantations in northern Taiwan. The abundance order of all ions was Cl- > Na+ > SO42- > K+ > NO3- >NH4+ >Ca2+ >Mg2+ inrainwaterandNa+>Cl- >NO3- >Mg2+ >SO42- > Ca2+ > NH4+ > K+ in fog water. Cl- and Na+ were the most abundant ions in both fog and rain water, indicating strong oceanic influences on water chemistry. The concentrations of all ions were much higher in fog water and the ratio to fog and rain was K+ (2.11) < NH4+ (5.59) < SO42- (6.99) < Ca2+(9.25) < Cl- (9.26) < NO3- (10.3) < Na+ (14.2) < Mg2+ (22.2) < DON (46.9), which lies between sites with (mostly were larger than 10) and without (less than 5) major emission, possibly because the study site is close to big cities but the surroundings are well covered with forest. Results from principal component analysis indicates that agriculture influence is the main factor for explaining variance of K+ and NH4+ concentrations in fog water but not rain water. The result indicates that fog was more affected by local air pollution. The amount of Ca2+ and Mg2+ in throughfall is higher than in rain water possibly because canopy leaching. Moreover, the negative relationship between net throughfall flux and its concentration in rain water for most ions suggested that passive movement was important in characterizing throughfall dynamics.

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