利用X光螢光掃描技術探討蘭陽源匯系統人與環境之互動關係

An Investigation of Environment-Human Interactions in the Lanyang Source-to-Sink System Based on X-Ray Fluorescence Scanning Analysis

黃致展(Jyh-Jaan Huang)

指導教授 ： 魏國彥

共同指導教授 ： 宋聖榮 ； 施路易(Ludvig Löwemark)

國立臺灣大學/理學院/地質科學研究所/博士(2016年)

https://doi.org/10.6342/NTU201603863

摘要

在全球環境變遷的衝擊之下，人與環境相依而又衝突的關係受到社會大眾前所未有的關注。透過檢視地質紀錄與人類歷史，人與環境過往的相互作用可提供一個鑑往知來的類比，以做為人類下一步該何去何從的參考。然而，人與自然的互動關係在自然紀錄中常如曇花一現般轉瞬即逝，在重建上也因此更具挑戰。有鑑於此，本研究使用快速而非破壞性的岩芯X光螢光掃描技術，以提供岩芯在公釐尺度上的元素含量變化，做為解析過往訊息的手段以及後續其他分析的基礎。然而傳統上認為，對單點的掃描時間越長，其累積的訊號越能有效降低分析的誤差，但在高解析度的研究中，提高掃描時間卻會降低分析的效率並大幅提升掃描的成本。本研究以Itrax岩芯掃描儀針對一系列地質標準品進行單點掃描時間和X光管靶材的技術測試，由掃描結果和標準品元素含量的比較顯示，掃描時間的長短對於測量準確度之影響並不顯著。在此基礎之上，本研究即可使用較短的掃描時間，以發揮岩芯掃描技術快速而高解析度的特長，重建蘭陽源匯系統過去千來以來的環境變化，並進而參照歷史和考古資料，討論人與環境的相互作用。
在歷史時間尺度上，本研究以宜蘭梅花湖的湖芯配合多重代用指標以及落塵核種定年，重建臺灣首個過去150年以來高解析度的湖泊紀錄，結果顯示近代人類在湖岸的大型建設以及漢人開蘭的農業活動，皆對其周遭的環境產生衝擊且被記錄於湖泊沉積物中。此外，由蘭陽平原淇武蘭遺址的文化遺留和碳定年結果顯示，淇武蘭文化在西元1150-1350年之間曾出現了一文化間斷，本研究以源匯系統的概念，整合蘭陽溪上游的階地定年、蘭陽平原南北兩側的湖泊沉積物以及沖繩海槽與和平海盆的海洋沉積物資料，重建過去1200年以來蘭陽源匯系統的河川加積紀錄，以期能對此一文化空白時期提出解釋。研究結果顯示，蘭陽源匯系統於西元875-925以及1400-1500這兩個時期皆有顯著的河川加積現象，但皆明顯早於或是晚於淇武蘭遺址的文化空白時期。這顯示淇武蘭遺址下文化層的消亡應為一相對獨立的事件而非肇因於影響整個流域的自然災變，本研究因而認為蘭陽溪與其支流於在平原區頻繁的河道遷徙，可能才是造成遺址內文化空白的原因。本研究透過重建蘭陽源匯系統的自然紀錄與人類歷史，在不同的時間和空間尺度上探討人與環境的交互作用，將可對臺灣河川沉積物的產生和輸送機制，天然災害的預防及減災，以及土地的永續管理提供重要的背景資料。

關鍵字

蘭陽源匯系統 ； Itrax岩芯掃描儀 ； 環境變化 ； 人類活動

並列摘要

In the concerns of global environmental changes, the discussions of the relationship between human and its surrounding environment have become unprecedentedly popular. By investigating the geological records and human history in the past, the interactions between nature and human activities provide precious analogs illuminating our fate in the future. However, the abrupt and rapid signals of human-environment interactions are often difficult to decipher from natural archives. Therefore, this study made the use of the fast and non-destructive micro X-ray fluorescence (XRF) scanning technique to reveal the detail down-core elemental variations directly from the untreated sediment at sub-mm resolution. To improve our utilization of the XRF scanning technique, six geological reference materials were scanned by the Itrax-XRF core scanner with different exposure times with the Mo and Cr X-ray tubes to allow a comparison of resulting intensity counts with absolute concentrations. The results show that the degree of the accuracy of the measurements does not necessary increase with increasing exposure time. On this basis, the paleoenvironmental changes of the Lanyang Source-to-Sink System over the last millennium can be reconstructed efficiently using a short, optimal exposure time, allowing the signals of human-environment interactions to be discerned and captured.
Three cores from Lake Meihua in northeastern Taiwan were studied by a multiproxy approach, providing the first decadal-resolution lacustrine records over the past 150 years in Taiwan. With the establishment of a precise chronology based on the radionuclides, this suite of lacustrine sediments has recorded the signals of human activities, such as the construction of temples and the onset of agricultural practices, in agreement with historical documents. Moreover, according to archaeological evidence, a cultural hiatus of 1150-1350 cal. yr AD from Site Kiwulan has been recognized. The early settlement of aboriginal Kiwulan people was abandoned for around two hundred years before being recolonized. To provide a possible explanation for this cultural break, multiple lines of evidence obtained from the source areas (upland river terrace), the floodplain lakes, and the ultimate sink (the southern Okinawa Trough and Hoping Basin) in the Lanyang Source-to-Sink System have been studied to reconstruct the river aggradation history over the last 1200 years. Two particular river aggradation periods, namely 875-925 cal. yr AD and 1400-1500 cal. yr AD, have been found and they occurred significantly earlier and later than the cultural hiatus, respectively. A hypothesis of “river channel migrations” thus be proposed to explain the culture hiatus enigma, instead of collaborating with the “climate change” hypothesis suggested by previous studies. By disentangling the nature variation and anthropogenic impacts of the Lanyang Source-to-Sink System at different temporal and spatial scales, this study is able to address issues of natural disaster prevention, land-use management, and sustainable environment governance.

並列關鍵字

Lanyang Source-to-Sink System ； Itrax-XRF core scanner ； Environmental changes ； Human activities

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