- 學位論文
台灣東部雷公火泥火山沉積物岩芯之孔隙水地球化學特性及其微生物活動隱示
Geochemical characteristics of sediment cores of the Lei-Gong-Huo mud volcano, eastern Taiwan and its implications to microbial activity
摘要
近年來地球暖化是個備受矚目的議題，造成暖化的原因多歸咎於過量的溫室氣體。其中甲烷所造成的溫室效應為二氧化碳的二十倍以上。因此，甲烷在大氣中的循環與濃度變化對於暖化具有重要的影響。而全球甲烷多半來自於人為活動產生，部分為天然環境釋出。人類對天然環境的瞭解仍有許多未知的部分，在已知的環境中，冷泉系統和泥火山皆為甲烷逸散的地質構造。台灣位於聚合帶上是一個適合泥火山發展的環境，可在台灣西部、東部發現泥火山的存在。 本研究選擇位於台灣東部關山地區的雷公火泥火山為研究題材，其目的為探討此區域泥火山地質微生物地球化學。藉由在此區的五個不同噴口採集深度約五十公分的沈積物岩芯，依固定間距將岩心分段並分門別類保存樣本。主要測量孔隙水中陰、陽離子濃度 (包含氯、鈣、鈉、鉀、鍶、鎂、硼、鋇、二價鐵、錳及硫酸根離子)、烷類氣體含量及其相對碳同位素值、酸化孔隙水取得鹼度、沈積物含水量。 實驗結果顯示六根岩芯所呈現的化學特徵都不太相同，含水量隨深度的變化可歸類為三種趨勢，分別為接近地表大於底部含水量、隨深度增加含水量緩慢減少、呈現波動形式。二價鐵和錳濃度隨深度變化分為表層含量高在底層遞減、表層含量低隨深度遞增、表層和底層濃度高於中間的三種類型。甲烷濃度與鹼度變化分為底層較高並向上遞減、中間濃度大於表層與底層、表層濃度向下遞減。剩下的元素與氯離子隨身度的變化呈現一致的關係為向下遞減的剖面。 根據上述地球化學結果並配合過去對此區域微生物研究，此區消耗甲烷的機制與海洋環境中配合硫酸還原菌而氧化甲烷的機制不相同。在微生物研究方面目前初步推測與鐵錳還原菌有相關。未來將進一步分析同位素值，以瞭解甲烷氣體來源以及向上逸散過程是否受到微生物作用影響。除了生物作用影響之外，天然環境中各成分濃度變化也受控於自然蒸發沈澱等作用。
並列摘要
Global warming is a high-profile issue in recent years, which is considered to be caused by excessive greenhouse gas emission. Methane is a potent greenhouse gas. Compared with carbon dioxide, it has a high global warming potential, the greenhouse effect caused by methane is twenty times higher than carbon dioxide. Therefore the methane has the important influence in atmosphere circulation and the concentration change for the warming. Most of atomspheric methane comes from human activities, in part by the release of the natural environment. It is still conclusive how methane is released to the natural environment. However, cold seeps and mud volcanoes system is a major geological structure of methane emission in the natural environment. Taiwan is located in the convergent continental plate for development of terrestrial mud volcanoes. Thus the terrestrial mud volcanoes in Taiwan’s southwest and eastern become an important issue of the release methane mechanism in nature research. This research focus on Lei-Gong-Huo mud volcano, eastern Taiwan, the goal is to discuss the characteristic of geochemistry microorganism in this area. Drill six sediment cores at different vents. With the fixed space to cut apart the core and following analysis preserve the sample. Measure sediment water content, the pore water alkalinity, cat ion and anion concentration (contains Cl, Ca, Na, K, Sr, Mg, B, Ba, Fe2+, Mn2+ and SO42-), and the dissolved hydrocarbon alkanes gas concentration. The analysis result discovered six cores display different chemistry characteristic. Water content with depth display three trends were the shallow increased and then decreased in the bottle, the maximum under the surface layer decreases slowly with increasing depth, and display a fluctuation variation. The ferrous iron and divalent manganese concentration also display three types with the depth change, which the surface layer concentration higher then bottom, the surface layer concentration increase progressively with depth, the surface layer and bottom layer higher than the center-section. The methane concentration and alkalinity are also have three types, respectively is the surface layer is high and upward decreasing progressively, the center-section concentration is higher than the surface layer and the bottom layer, surface layer concentration downward decreasing progressively. Other ion concentration and chloride ion concentration change with depths are consistent relations, mostly downward gradually decrease. The geochemical analysis display that the most ions concentration should be controlled by inorganic mechanism of evaporation, precipitation, and sedimentation. Methane consumption difference with marine sedimentary environment, there is no Sulfate reduction and methane oxidation co-consumption characteristics, but the ferrous iron and divalent manganese concentrations significantly correlated with methane, represent perhaps the iron and manganese reduction co-consumption with oxidation of methane. In the past microbial biology research at Lei-Gong-Huo, it’s also speculated that methane consumption related to iron- and manganese-reducing bacteria. Further analysis in the future, measure carbon isotopic composition of hydrocarbon alkanes and dissolved inorganic carbon in order to understand the source of methane gas and the upward dispersion of the process by microorganisms.