| 摘要: | 淡水河為台灣第二大河，其主流及支流流經新竹縣、桃園縣、新北市、台北市以及基隆市，人口聚居超過七百萬人。由於大量的都市及工業廢水排入，造成嚴重的汙染。本研究為了瞭解淡水河流域內之營養鹽及溶氧等變化，於2009年2月與7月進行了兩次流域採樣。分析結果得知淡水河上游氮、磷營養鹽濃度皆很低，水體內的氮營養鹽以硝酸根為主(約5~40μM)，溶氧則接近飽和(約300μM)。到了人口較稠密之大台北都會區時，隨著汙染物注入河川，氮磷營養鹽快速上升(銨離子約200~300μM；磷酸根約5~40μM)，水體內的氮營養鹽變成以銨離子為主。溶氧由於有機物分解及硝化作用等耗氧作用而快速下降(溶氧約50~200μM)，部分河段呈現缺氧之情形。到了接近出海口的地方，因為海水的混合才使得營養鹽濃度下降、溶氧上升。 為了瞭解污水處理廠放流水對該處河川水體之影響，與重陽橋水體之葉綠素變化周期，本研究於2010年5月至2011年8月進行每周一次之重陽橋水體採樣，2010年5月至2011年4月進行每個月一次之污水處理場採樣。將重陽橋與迪化汙水廠之採樣分析結果經過計算後得知迪化污水處理廠的排放水之銨離子約只佔淡水河該河段之銨離子通量之7.5%，磷酸根約只佔16.5%。且在該河段之氮、磷營養鹽並非特別高，故可得知污水處理廠之排放水並非淡水河中氮、磷營養鹽之主要來源。將重陽橋之銨濃度時間序列經由HHT分析可以看出其濃度之季節變化以10月最低，此月之流量最高，顯示有稀釋作用。磷酸根濃度則沒有明顯之季節變化。葉綠素濃度在乾潮時呈現夏天高冬天低的週期變化，其季節變化周期可能與日照之強度與溫度有關。 為了解淡水河流域近年水質之變化，本研究利用水利署自2005年10月至2011年12月於大漢溪內之浮洲橋站、新店溪內之華中橋站、基隆河內之大直橋站與淡水河內之重陽橋站每月一筆之銨濃度資料，經由HHT分析淡水河流域內各測站銨濃度之變化，發現淡水河及其支流水體的銨濃度皆有下降之趨勢。可能因為近年來大台北地區污水下水道的接管率提升，排入河川中的汙染物減少。 為了探討淡水河中主要之物理及生地化反應過程及其通量，本研究利用一維河流模式模擬淡水河及其主要支流大漢溪中鹽度、銨離子濃度、硝酸根濃度、葉綠素濃度及溶氧之變化，得到不錯的結果。並計算出淡水河三鶯大橋至挖仔尾河段中主要之銨氮來源應為樹林、土城一帶之污水點源排放，約佔總來源之4成，支流與污水廠輸入之銨氮總共約佔來源之4成，有機物在河道中分解所生成之銨氮約只佔2成，污水廠排放之銨氮占總來源之1成以下。淡水河水體中約8成的氨氮直接經由出海口排入海洋之中，只有約2成之銨氮經由硝化作用及初級生產被消耗掉。此河段溶氧之來源主要有水氣交換與初級生產，分別佔總來源約5成與3成，上游輸入之溶氧約佔總來源之1成。耗氧之主要因素為有機物分解，約佔了氧氣消耗的7成，硝化作用則約佔了總耗氧之1成，其餘約2成之溶氧由出海口排入海洋中。利用模式模擬結果計算12月淡水河輸出之DIN通量約為1.44*10^6mole/day，較前人(Wen et al., 2008)對2001年12月之計算結果(2.15*10^6mole/day)為低。此與水利署淡水河內銨濃度數據所顯示之下降之趨勢一致。但許多河段內尚存在相當高濃度銨及低溶氧，可見雖經整治但仍有相當可觀之汙染源排放進入河川之中。 The Danshuei River has the second largest drainage basin in Taiwan with the river basin spanning across Hsinchu county, Taoyuan County, new Taipei City, Taipei City and Keelung City. The total population in the drainage area exceeds 7 million. Based on previous studies, high levels of water pollutants were found in the Danshuei River. Because of the importantce of the Danshuei River to the inhabitants, we conducted this study on its water quality. This study is to investigate the distribution of nutrients and dissolved oxygen in the Danshuei River and its tributaries and to understand what controls the variation. The results show that, in the upper reach, the concentrations of nitrogen- and phosphorus-bearing nutrients were low and the nitrogen species were dominated by nitrate (5-40 uM), while the dissolved oxygen value was approaching saturation (300uM), during water sampling trips in February and July 2009. As the river water flowing closer to the metropolitant area, the nutrient concentrations increased dramatically (with ammonium up to about 200-300um, and phosphate up to about 5-40uM) and the dissolved oxygen decreased rapidly (down to 50-200uM) because of waste water inflow. The nitrogen species were now dominated by ammonium (5-40 uM). The dissolved oxygen concentration decreased rapidly to 50-200uM due to decomposition of organic matter and nitrification of ammonium. The concentrations of nutrients began to decrease and dissolved oxygen began to increase, when the river water was approaching the sea in the lower reach. In order to investigate the seasonal variation of water quality and how discharges from sewage treatment plant affected water quality, we conducted weakly water sampling at Chunyang Bridge from May 2010 to August 2011 and monthly sampling from sewage treatment plant. The results show that the contribution of ammonium to the Danshuei River by the Dihua sewage treatment plant was 7.5%, and that of phosphate was 16.5%, indicating discharges from sewage treatment plant was not the dominant source of nutrients in the Danshuei River. Data analysis of the weekly sampling results by the HHT method shows seasonal variation of ammonium over the annual cycle with the lowest value in October, when the discharge was the highest, suggesting dilution effect. By contrast, the phosphate data showed no seasonal trend. The concentration of chlorophyll was the highest in summer and lowest in winter, probably reflecting the variation of the intensity of light. For better understanding of the trend of water quality in the past few years, we analyzed, using HHT, ammonium data from October 2005 to December 2011 observed at the Fuzhou station of the Dahan River, the Huazhong station of the Shindian River and the Dazhi station of the Keelung River provided by EPA. The results show decreasing trends for concentrations of ammonium in the drainage basin of Danshuei River, Probably attributable to the increasing construction of sanitary sewer systems. A one dimensional advection-diffusion-reaction model has been applied to simulate the variations of salinity, ammonium, nitrate, chlorophyll and dissolved oxygen along the main channel of the Danshuei River. The purpose is to evaluate the reaction rates and related physical parameters. The results show that the dominant sources of ammonium probably originated from the Shulin and Tucheng areas, which contributed about 40% of the total input, while the tributaries and sewage treatment works contributed another 40% and degradation of organic matter provided the last 20%. 80% of the ammonium was discharged to the sea, while only 20% was consumed by nitrification and phytoplankton growth. Concerning the input of dissolved oxygen, aeration of surface water and primary production contributed 50% and 30% respectively, while only 10% came from upstream. Concerning consumption of oxygen, 70% was by organic degradation, 10% by nitrification, and the last 20% was discharged to the sea. For December 2009, the model predicted total discharge of DIN was 1.44*10^6 mole/day, which was lower than previously reported discharge of 2.15*10^6 mole/day for December 2001; this is consistent with the trend found in the EPA data. Despite the improved water quality, the pollution in the Danshuei River was still serious, suggesting significant pollutant sources still existed in the drainage basin. |
