- 學位論文
南海有光層中溶解性氮物種分析與季節變化初探
Pilot Study of Dissolved Nitrogenous Species in the Euphotic Zone of Oligotrophic South China Sea
摘要
海洋氮循環在控制生物幫浦，將大氣中的二氧化碳隱沒進入深海的過程中扮演著重要角色（Falkowski, 1997），在過去的研究報告中指出，南海的環境有利於固氮作用的發生，並且藉由硝酸鹽的觀察中發現了固氮的證據（Wong et al., 2002），在本研究中我們除了試圖研究季節性變化外，亦想藉由二十四小時以上的連續觀測，從氮物種的日夜變化中找出氮通量可能未知的部分，並且從氨氮、亞硝酸鹽或是溶解性有機氮的連續觀測中探索海洋氮循環的機制，以及海洋生物固氮的直接證據。本研究參與了由國家海洋科學研究中心（NCOR）執行的「南海時間序列研究」SEATS（South East Asia Time-series Study）計畫航次，在南海 KK1測站，自2002年11月至2004年3月間測量各季節氮物種的垂直分佈。 本研究分別採用靛藍法測氨氮（Pai et al., 2001），亞硝酸鹽利用磺胺奈乙二胺呈色法測定（Pai et al., 1990），硝酸鹽使用鎘銅還原流動注入分析法測定（Pai and Riley, 1994），以及紫外光線照射添加過硫酸鹽氧化劑法測總氮，溶解有機氮部分則由總氮扣除各無機氮物種求得（Bronk et al., 2000）。研究發現在南海有光層內溶解態氮物種以有機氮的分佈居多。浮游生物族群的富集層，深度約介於60公尺處，氨氮、亞硝酸鹽及溶解性有機氮都有相對濃度最高值，而硝酸鹽在此深度以下也開始出現，濃度隨深度遞增。而深度較游生物富集層淺之處（∼40公尺）亦隨時間不同會出現的另一個氨氮濃度高值，可能是固氮作用造成的。本研究期間內，南海有光層中亞硝酸鹽濃度相對極大值最高值出現於夏季，濃度約可達到0.4 uM，冬季時亞硝酸鹽在次表層的相對極大值濃度雖然降低，最低僅有0.15 uM，而在垂直分佈上，冬季時亞硝酸鹽分佈的水層則明顯較夏季時為厚。硝酸鹽濃度出現的深度有顯著的季節性變化，夏季時比春、冬兩季為淺，季節性的變化可能與水體密度層結構改變有關。
並列摘要
The marine nitrogen cycle plays a major role in controlling the biological pump and the environmental conditions of South China Sea (SCS) that are conducive to the study on nitrogen cycle and possible importance on nitrogen fixation. Using nitrate anomaly as precursor, Wong et al., (2002) had indicated that significant contribution of the re-mineralization of nitrogen-rich organic matter were formed by nitrogen fixation. In this study, a series of in-situ and ln-house analysis were performed to demonstrate the seasonal variations of dissolved nitrogenous species and its diurnal variations. Which observed as the first time in South China Sea, completed vertical distributions of various dissolved nitrogen, including nitrite, nitrate, ammonium and dissolved organic nitrogen (DON). In hope to better understand the nitrogen cycle and gain direct evidence of nitrogen fixation. As part of the supporting works for SEATS (South East Asia Time-series Study) program of NCOR, researches were conducted during November 2002 to March 2004. In this work, nitrite was measured by standard pink azo dye method and ammonium was measured by improved indophenol blue spectrophotometric method. Nitrate was measured by cadmium reduction flow injection analysis method. Total dissolved nitrogen (TDN) was first converted to nitrate by UV photo-oxidation method with addition of persulfate. It is found that, In the euphotic zone (0-200m) DON were the dominate species in the TDN pool. Ammonium, nitrite and DON have highest concentrations in depth 60-80m, correspondent to the chlorophyll-a maximum layer. In addition, during different time, a secondary ammonium concentration maximum can also be found at shallower depth (~ 40m) may be caused by the occurrence of nitrogen fixation. In this study, highest nitrite concentration was found in summer, and lowest appeared in winter. However, the thickness of nitrite distribution in winter is greater than in summer. Result also indicated that the nitrate nutricline in SCS varied seasonally possibly caused by water column structure.
參考文獻
延伸閱讀
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