- 學位論文
臺灣山地河流中溶解性有機碳的動態變化及其與無機氮的耦合關係
DOC Dynamic and Its Coupling with DIN in Small Mountainous Rivers, Taiwan
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摘要
溶解性有機碳（dissolved organic carbon，DOC）為水中微生物成長的能量來源，調節各種生物和化學作用，是維持溪流生態系結構和功能運作的關鍵物質。然而，目前人們對於河流中DOC的瞭解仍然相當有限，包含DOC在河網的傳輸過程，以及它與氮的耦合循環。尤其在降雨豐沛、地形陡峭的亞熱帶高山型島嶼溪流，DOC的相關研究更是缺乏。因此，本研究旨在探討臺灣山地河流的內部與外部作用，如何共同影響DOC的動態變化及其與溶解性無機氮（dissolved inorganic nitrogen，DIN）的耦合循環。結果顯示，臺灣河川中的DOC具有低濃度、高輸出量的特性。與世界大型河流相比，年徑流量、坡度和土壤有機碳（soil organic carbon，SOC），仍是估計DOC輸出量的有效因子，但其影響的強度與方式卻與世界其他河流截然不同。SOC是臺灣河流中DOC的重要來源，其含量主要受植群分布的影響，沿海拔垂直變化；而陡峭的地形，造成集水區普遍土壤淺薄且流速快，進而限制了DOC的生產和累積。颱風期間，濃度與流量的關係，呈現順時針的遲滯迴圈，表示濱岸帶或下坡處，是水文歷線上升段DOC的主要來源。過去的研究指出，水生系統中，DOC與DIN之間普遍會呈現非線性的負相關。然而，我們研究發現，臺灣河川在溶氧充足的狀態下，不論是低度或高度人為干擾，都不會出現這樣的反向關係，顯示可能存在碳限制的狀況；唯有在高度人為干擾，且溶氧不足的狀態下，才會出現DOC與NO₃⁻-N之間非線性的負相關，同時，過量的DIN會以NH₄⁺-N的形式累積，控制機制也從能量限制轉變為氧化還原限制。本論文闡述了高山型島嶼溪流中，控制DOC動態變化，以及DOC與DIN關係轉變的主導因素，為瞭解環境變遷下河流碳氮循環，提供了新的基礎科學知識。
並列摘要
Dissolved organic carbon (DOC) provides energy for microbial growth and regulates various ecological and chemical processes in aquatic ecosystems. However, our knowledge of riverine DOC dynamics and its coupling with nitrogen remains limited, especially in subtropical small mountainous rivers (SMRs) characterized by abundant rainfall and steep slope. This dissertation aims to unravel how external drivers and internal processes affect DOC dynamics and its coupling with dissolved inorganic nitrogen (DIN) in Taiwan SMRs. Our results showed that Taiwan SMRs have low DOC concentration but high yield. Compared to rivers worldwide, the annual runoff, slope, and soil organic carbon (SOC) have demonstrated their efficacy as reliable predictors for estimating DOC yields, aligning with expectations, although they exert different influences. The presence of SOC stocks associated with elevation-dependent biomes is likely a key regulatory factor governing the supply of DOC, while the influence of slope appears to play a role in limiting the generation of DOC. Additionally, the observed clockwise hysteresis in concentration－discharge relationships provides evidence that the riparian zone or downslope area is the main source of DOC on the rising limb of the hydrograph. Furthermore, the commonly recognized inverse relationships between DOC and DIN are not present in the well‑oxygenated watersheds, regardless of low or high human disturbance. The significant inverse relationship between DOC－NO₃⁻-N would only be evident in watersheds that are highly disturbed and characterized by low levels of dissolved oxygen. The transition of DOC－DIN relations from energetic to redox constraints in low-DOC rivers might be strongly controlled by the availability of dissolved oxygen in rivers. Overall, this dissertation elucidates the dominant factors controlling DOC dynamics and the transition of DOC-DIN relationships in Taiwan SMRs. These findings provide a solid foundation for assessing the distribution and fate of carbon and nitrogen in riverine environments amidst the rapidly changing conditions of our world.
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