淡水河位於台灣北部，氮營養鹽排放濃度比世界上多數大河都高[Wen et al., 2008]，其優養化現象造成淡水河中下游河段往往有嚴重的低氧狀態發生。故本研究為了解造成低氧的原因，於2014年10月至2015年8 月觀測了淡水河中下游河段之營養鹽濃度與溶氧變化。此外為了解淡水河下游河段之氧氣消耗及生產的機制，本研究測定了群聚呼吸率(Community respiration, CR)和初級生產力(Primary production, PP)。 研究結果顯示淡水河口低氧區段發生於距出海口20-30公里處的中興橋(D3)至城林橋(D7)，尤其秋季較為嚴重。淡水河氧氣消耗的主要過程CR平均為111.2 ± 14.3 mmol O2 m-3d-1且在D3-D7有較強烈的有機物分解，最高可達266.2 mmol O2 m-3d-1；氧氣產生過程PP平均為13.2 ± 4.03 mmol O2 m-3d-1，在柑園橋(D9)和三鶯橋(D10)為初級生產力最高的地點，最高可達50.4 mmol O2 m-3d-1。與世界其他河流相比，淡水河的PP較其他河流來的低且CR遠遠超過其他河流。 本研究的CR與PP數值與前人以淡水河生地化模式[林, 2015]所模擬出的結果比較，本研究的PP的分布與實測相似。但是CR實測值皆遠高於模式估算，高出25-120mmol O2 m-3d-1，顯示現實的氧氣消耗與生產機制較模式中所推估的還要複雜，仍需進一步研究驗證。 ;The Danshuei River is located in northern Taiwan, where the nitrogen concentration is higher than the most rivers in the world [Wen et al., 2008]. The eutrophication phenomena in the Danshuei River sometimes led to severe hypoxia. In order to understand the occurrence of the hypoxia, we surveyed nutrient concentration, chlorophyll a and dissolved oxygen in the Danshuei River during October 2014 to August 2015. In addition, I measured the community respiration rate (CR) and primary productivity (PP) to understand the mechanisms of the consumption and production of oxygen in the Danshuei River. The results show hypoxic zones of the Danshui River occurred in 20-30 km away from the estuary, from the Zhongxing Bridge (D3) to the Chenglin Bridge (D7). The most serious hypoxia occurred in the fall. The averaged CR was 111.2 ± 14.3 mmol O2 m-3d-1. Higher oxygen consumption occurred at D3-D7 where the highest CR reached 266.2 mmol O2 m-3d-1. The averaged primary production was 13.2 ± 4.03 mmol O2 m-3d-1. The highest PP occurred at Ganyuan Bridge (D9) and the Sanying Bridge (D10) was 50.4 mmol O2 m-3d-1. Comparing the measured PP and CR in Danshuei River with that in other rivers around the world, we found that the measured PP in Danshuei river is relatively low, and the measured CR is much higher than that in other rivers. Comparing to the biogeochemical modeling results, the distribution and magnitude of PP I measured were similar to previous modeling results in Danshui River [Lin, 2015]. However, the measured CR were all much higher than previous modeling results (25-120 mmol O2m-3d-1). The biogeochemical model used by Lin (2015) can not well describe the mechanism of oxygen consumption and production, and more investigations are needed for model verification.
