| 摘要: | 摘 要
淡水河為台灣第二大河，集水區域人口總數達800萬人，人為污染造成淡水河有優養化以及季節性的缺氧的情形。本研究為了解淡水河優養化與缺氧的程度，於2013年至2014年期間，量測了淡水河主流的鹽度、溶氧、葉綠素、營養鹽、顆粒碳與氮，並以FEMME (Flexible Environment for Mathematically Modelling the Environment) 模式研究造成優養化以及缺氧的機制。
量測結果得知淡水河主流的中上游部分(離河口39~96公里)水質較佳，溶氧接近飽和狀態(>274 M)，氮營養鹽濃度皆低(<82.2 M)，水體內的氮營養鹽以硝酸根為主(佔89%)。到了人口較稠密之大台北都會區時(離河口14~39公里)，水質漸趨優養化，溶氧逐漸下降(最低達102 M)，氮營養鹽濃度逐漸上升(最高達334 M)，水體內的氮營養鹽以銨離子為主(佔73%)。而在近出海口時(離河口0~14公里)，受海水混合影響，平均溶氧上升至174 M，平均氮營養鹽下降至35.9 M，水體內的氮營養鹽以銨為主(佔65%)。
由FEMME模式計算結果得出在淡水河主流中，最主要移除溶氧之途徑為下游平流輸出(占51.3%)，其次是有機物分解(占38%)；而溶氧的主要來源為平流輸入(占52.2%)，其次是初級生產(占21.5%)。銨的主要來源為支流與汙水設施輸入(占86.6%)，其次是有機物分解(占10.1%)；銨的移除途徑主要為下游擴散(占73.6%)，其次是下游平流輸出(占13.1%)，然而淡水河河道內生化作用不顯著。
由環保署的歷史資料分析結果得知，淡水河主流與支流中之溶氧濃度大多呈現逐年上升趨勢，氨離子濃度呈現逐年下降趨勢，說明淡水河水質隨著汙水接管率提高而逐年改善。藉由FEMME模式情境模擬得知，如將浮洲橋附近之點源汙染移至下游注入，即能藉由潮汐擴散的幫助將汙染物移出淡水河，解決浮洲橋區間缺氧的現象。
;Abstract
The Danshuei River is the second largest river in Taiwan. The population in its watershed is over 800 million. The high population causes the eutrophication and seasonal hypoxia. In this study, the seasonal variation of salinity, dissolved oxygen, chlorophyll a, nutrients and particulate carbon and nitrogen from Shimen reservoir to Danshui River estuary during 2013 to 2014 were surveyed and analyzed by FEMME (Flexible Environment for Mathematically Modelling the Environment) model in order to understand the magnitude and mechanism of eutrophication and hypoxia.
Based on the observations, the water quality in upstream (39 to 96 kilometers from the estuary) of the Danshuei River is better than that in midstream and downstream. Dissolved oxygen was close to saturation (> 274 M), nitrogen nutrient concentration was low (<82.2 M), and nitrate was the dominant component of DIN(dissolved inorganic nitrogen) (accounting for 89%). The water quality in midstream (14 to 39 kilometers from the estuary) of the Danshuei River where is close to a highly populated area was more eutrophic than that in the upstream of the Danshuei River. From upstream to midstream, the dissolved oxygen decreased (minimum of 102 M), the DIN concentrations gradually increased (maximum 334.2 M), and ammonium became the dominant component of DIN (accounting for 73%). However, the water quality in the downstream (0 to 14 kilometers from the estuary) of the Danshuei River was better than that in the midstream because of the mixing with seawater. From midstream to downstream, the average dissolved oxygen increased to 174 M, average nitrogen nutrients decreased to 35.9 M, and ammonium was still the dominant component of DIN(accounting for 65%).
The FEMME modeling results showed that dispersion is the most important sink source of dissolved oxygen in Danshuei River in downstream (accounting for 51.3%), which is followed by decomposition of organic matter (accounting for 38%). The main source of dissolved oxygen is dispersion inputs (accounting for 52.2%), which is followed by primary production (accounting for 21.5). The main source of ammonia is tributary and sewage input (accounting for 86.6%), followed by the decomposition of organic matter (accounting for 10.1%). The main sink ammonium is downstream diffusion (accounting for 73.6%), followed by dispersion (accounting for 13.1%). The biochemical processes is not an important source or sink of ammonia and dissolved oxygen. .
Historical data from Environmental Protection Agency suggested that the dissolved oxygen concentration rose in the Danshuei River mainstream and all tributaries except for Fu-Zhou bridge in Dahan River. The increasing sewage treatment rate in Taipei may be one of the reasons of the improvement of water quality in Danshuei River. But, the sewage discharge was focused in Fu-Zhou bridge section that deteriorated the water quality at that region. Scenario simulations done by FEMME model show that to move the sewage discharge from Fu-Zhou bridge to Dihua sewage treatment plant in downstream would significantly improve the water quality since the pollutant can be fast diluted by the tidal mixing. |
