應用LOADEST評估氣候變遷情境下河川輸出溶解態有機碳之變化 ── 以翡翠水庫上游集水區為例

Abstract

台灣為亞熱帶地區多高山的小島國家，過去研究顯示，台灣的高山小河川在陸域有機碳輸出至海洋的過程中扮演重要角色，大部分研究的重點著重顆粒態有機碳輸出而鮮少討論溶解態有機碳輸出的重要性，然而，單位面積溶解態有機碳的年產出量高達每公頃30公斤，全球排名前30%。故本研究以坪林集水區為例，利用過去近十年之溶解態有機碳觀測資料，透過汙染物負載量計算模式Loadest建立溶解態有機碳輸出之統計回歸模型，並進而推估5個GCM在RCP8.5氣候變遷情境下，於短期、中期一、中期二與長期，溶解態有機碳輸出之變化。 研究成果顯示，氣候變遷情境下，短期、中期一、中期二與長期下，多數模式顯示，年總溶解態有機碳輸出量並無顯著變化；然而冬、春兩季溶解態有機碳輸出量有在短期、中期一、中期二與長期皆有減少，且最多可減少達30%的趨勢，長期將降低達37%；夏季則隨時間其增加在CSIRO模式下有增加趨勢。整體而言，在氣候變遷情境下，多數模式皆呈現減少之趨勢，即意味，未來，冬、春兩季水體內溶解態有機碳輸出將大幅減少，而夏、秋兩季則隨情境不同，輸出差異越大，但大抵呈現減少之趨勢。

Taiwan is a subtropical mountainous island country. The previous studies indicate that alpine streams in Taiwan play an important role in the process of exporting terrestrial organic carbon into the ocean. Most studies emphasize on the importance of particulate organic carbon but rarely discuss on the importance of dissolved organic carbon. However, the annual produce of dissolved organic carbon per unit area in Taiwan is as high as 30 kilograms per hectare, ranking at the 30% highest globally. Therefore, this study chooses Pinglin watershed as an example study area, and utilizes the pollution load calculation model, Loadest, to build a statistical regression model of dissolved organic carbon export from observation data in the near ten years. The data are further used to predict the difference of near-term, middle-term phase 1, middle-term phase 2 and long term dissolved organic carbon export of 5 GCMs under the climate change context of RCP 8.5. The results show that most models indicate no significant change in annual dissolved organic carbon export in near-term, middle-term phase 1, middle-term phase 2 and long-term time frame under climate change context. However, the dissolved organic carbon export in both winter and spring season declines in the near-term, middle-term phase 1, middle-term phase 2 and long-term timeframe. The decline of the trend can be as much as 30% and is expected to decline to 37% in long-term. The dissolved organic carbon export in summer shows an inclining trend in CSIRO model as time goes by. Overall, most model shows declination in trends under climate change context, meaning that dissolved organic carbon export in winter and spring will decline drastically in the future while that in summer and autumn will have an overall declining trend but differ greatly depending on the contexts.