大屯火山群地衣體之地球化學特性研究

Geochemical Study of Lichens at Tatun Volcano Group

官思妤(SSU-YU KUAN)

指導教授 ： 呂學諭

國立中正大學/理學院/地球與環境科學系應用地球物理與環境科學研究所/碩士(2015年)

摘要

大屯火山群位於台灣首都-台北市的西北方，雖然最後一次活動可能在20萬年前，但因鄰近重要都會區，相關的火山監測仍持續進行當中。現今大多是利用火山氣體或溫泉水來監測火山活動，但這些數據只能顯示短時間內的狀況，長時間的大氣平均值則無法被有效偵測。若利用地衣做為生物監測，地衣的生長階段中會持續累積大氣的汙染物於體內，則可顯示出長時間大氣所含的元素濃度。地衣可做生物監測是因它的營養源仰賴於大氣中的水分和無機鹽，使地衣不易受到基質的污染；並且地衣體沒有排泄機制，可有效累積元素。再者，地衣生長範圍廣泛，這些優勢均有利於利用地衣進行生物監測。然而在二氧化硫含量較高的地區，會影響地衣的生長，導致在大屯火山周圍的枝狀地衣相較匱乏；雖然如此，本研究仍採得為量不少的殼狀和葉狀地衣。
本研究以大屯火山群為中心，向周圍的採樣，代表火山地區的地衣樣本；非火山地區的樣本採集於宜蘭南澳古道，代表沒有受到火山活動所影響的地衣樣本。將樣本硝化後，利用感應耦合電漿質譜儀進行分析，即可對應出火山與非火山地區的大氣狀態，並加以討論。從主成分分析的結果可看出，非火山地區地樣本集中分布，可成為一端元成分。火山地區地樣本則由此端元成分出發，順著主成分1及主成分2兩種趨勢分布，推測可能是受到不同地火山噴氣口所影響。稀土元素分析結果，分別利用安山岩以及北美頁岩進行正規化，結果顯示兩地區的樣本均有MREE富集的現象，推測為地衣體在累積元素的過程中，產生分化作用所導致。火山地區樣本普遍存在Ce負異常的現象，可能為稀土元素在大氣傳輸時，受到氧化反應影響，推測在酸鹼度較低的環境中，稀土元素較易溶於水，使得氧化反應較容易發生，造成Ce負異常，但以懸浮微粒為主的非火山地區卻沒有此現象。後續將與火山氣體的比較，探討地衣體內所累積的重金屬元素與火山氣體的相對關係；且大屯火山群緊鄰都市區，人為所造成的空氣汙染對研究區域的影響，亦可加以研究。

關鍵字

大屯火山群 ； 重金屬 ； 地衣

並列摘要

Tatun Volcano Group (TVG) is located in the northwest of Taipei, the capital of Taiwan. Although the last activity was 200000 years ago, it is critical to monitor TVG because it is nearby metropolitan area. This study is part of the monitoring program and attempts to observe the geochemical relationship between lichen and volcanic gas. Lichens have been extensively used for monitoring atmospheric quality. Lichen can live in critical environments and can accumulate metals from atmosphere due to lack of excretion mechanism. Moreover, lichen can live long and growth in a low rate; therefore, lichen geochemistry can represent an average in a long term manner. In TVG, fruticose lichen can be seldom found due to the high concentration of SO2 in the atmosphere. However, foliose lichen and crustose lichen are not rare in the study area.
In this study, lichens were collected from TVG and Nan-ao Trail which is in non-volcanic area. The cations were measured by ICP-MS. The geochemical results were analyzed by principal components analysis (PCA). It shows that there is no significant difference among non-volcanic lichens and the non-volcanic lichens are located at an end-member of two distinct trends. It is believed that the non-volcanic lichens indicate a geochemical baseline in north Taiwan and two trends may represent the mixing between two different types of volcanic gases in TVG and geochemical baseline. In this study, rare earth elements (REEs) were also measured. The results of non-volcanic and TVG lichens were normalized by North America Shale and TVG andesite, respectively. Both obtain a flat REE pattern, which confirm that TVG lichens receive metals from volcanic origin and non-volcanic lichens give information of background geochemistry in north Taiwan. In addition, a middle REE enrichment and distinct Ce negative anomaly can be observed. According to the previous studies, middle REE enrichment may be achieved by the selected adsorption of middle REEs by organic matter and Ce negative anomaly can result from oxidation reaction during transportation in atmosphere. However, more solid evidences will be needed for confirmation.

並列關鍵字

Tatun Volcano Group ； Heavy Metals ； Lichen

參考文獻

李貽華,徐慈鴻,2006. 植物監測空氣汙染之發展. 行政院農業委員會農業藥物毒物試驗所技術專刊,第163期.

高善,林怡欣, 2003. 臺北市內湖區金面山地衣調查與空氣污染對地衣影響之探究. 台北科學教育月刊260卷,24-35.

賴明洲,2000. 台灣地衣類彩色圖鑑(一) . 行政院農業委員會.

Agnan Y., Sejalon-Delmas N., Probst A., 2013. Comparing early twentieth century and present-day atmospheric pollution in SW France: A story of lichens. Environment Pollution 172, 139-148.

Agnan Y., Sejalon-Delmas N., Probst A., 2014. Origin and distribution of rare earth elements in various lichen and moss species over the last century in France. Science of the Total Environment 487, 1-12.