亞熱帶地區高山溪流溶解性有機碳的輸出量以及在全球氣候變遷下的意涵

Dissolved Organic Carbon Flux from Three Subtropical Mountainous Rivers in Taiwan and the Implications in the Era of Climate Change

臺灣高山溪流在陸地輸送有機碳至海洋的過程中扮演重要的角色，但大部分的研究把重點放在顆粒性有機碳的輸出而鮮少探討溶解性有機碳的輸出。本研究以三條鄰近的臺灣高山溪流為例，計算其近十年溶解性有機碳輸出量，強調臺灣高山溪流在溶解性有機碳輸出的重要性及在全球暖化下可能的後果。結果顯示，儘管研究溪流的平均溶解性有機碳濃度（＜1.0 mg L-1）排名在世界所有觀測河川的後1％，但其單面積的產出量（～30 kg ha-1 y-1）排名於前30％；溼季的平均濃度比乾季濃度高30％與溫度呈正相關，且溶解性有機碳的濃度在颱風時期達最高，最高可達平均濃度的5倍。全年約有60％的有機碳輸出發生於溼季，但儘管每年受颱風影響的時間很短（約3％的觀測時間），颱風期間的貢獻達全年輸出量的29.5±13.8％。我們發現，高溫及颱風事件為臺灣高山溪流溶解性有機碳輸出的重要驅動力，全球暖化的影響下的增溫及增強的颱風，將提高河水中溶解性有機碳的濃度及陸地輸出溶解性有機碳至海洋的速度。

Small mountainous rivers (SMRs) are important　conveyors of the land-to-ocean organic carbon　export.However, relatively few studies have focused on dissolved organic carbon (DOC) compared to particulate organic carbon. In a long-term project (2002 to 2014), stream DOC was monitored in three neighboring subtropical small mountainous rivers of Taiwan. The objective was to highlight the high DOC yield in SMRs and reveal the implications for global warming. The mean DOC concentration of the studied systems (<1.0 mg L-1) is ranked in the lowest 1% world’s rivers. However, mean DOC yield (~30 kg ha-1 y-1) is ranked in the top 30%. A positive relationship exists between temperature and DOC concentration which is 30% higher in wet season than in dry season. And typhoon-induced discharge boosted the DOC concentration by 5 times. More than 60% of annual DOC export was flushed off in the wet (warm) season. Moreover, up to 29.5±13.8% of the annual DOC export was accounted for by typhoon events, which the invasion time occupied ~3% of the monitoring period. We conclude that higher temperature and typhoon events are important drivers of the land-to-ocean export of dissolved organic matter. Predicted future increases in temperature and frequency/magnitude of typhoon events will likely elevate streamwater DOC concentration and accelerate the transport of terrestrial carbon to the ocean.