淡水河流域鹼度、酸鹼值與主要離子 之時空變化

Temporal and spatial variability of alkalinity, pH and major ions in the Danshuei River Watershed

莊竣皓(Chun-Hao Chung)

指導教授 ： 劉康克

國立中央大學/地球科學學院/水文與海洋科學研究所/碩士(2007年)

摘要

淡水河流域地處台灣北部，其三大支流:大漢溪、新店溪及基隆河，不論在自然環境或人為環境上都有很大的差異。流域內的兩大水庫：石門水庫及翡翠水庫，分處於大漢溪及新店溪流域，是台灣北部地區供水主要來源，所以台灣北部地區居民用水的水質與淡水河流域之地球化學息息相關。水中的鹼度及主要離子的來源主要是岩石經由岩石之化學風化產生，再由地表及地下水傳送到河川中，所以研究區域性鹼度的變化可以了解當地化學風化對水質之影響。本研究也探討因生物作用及降雨造成的水質變化。水庫儲水之駐留期較長，因此其水質會受到生物作用之影響。此外，淡水河流域，冬夏雨水來源不同，冬季受到東北季風降雨之影響，而夏季則主要受到颱風所帶來雨水的補充，不同季節之雨水可能有不同之酸度，對水質之影響也不同。本研究主要的研究區域為翡翠水庫集水區、桃園大圳及淡水河三大支流:大漢溪、新店溪及基隆河，分別採集河水樣本，過濾後分析pH值、鹼度與主要離子。
本文分為三個部份，依序來探討影響鹼度的因素及其該區域中鹼度的變化。在翡翠水庫集水區的部份，主要是探討生物的作用對水質之影響，例如:光合作用使得鹼度增加、呼吸作用使得鹼度降低及微生物進行脫硝作用造成鹼度的產生，並討論水庫之分層現象及季節性變化對水質之影響。在桃園大圳部分，主要是探討不同雨水之酸度對於鹼度的影響。鹼度在季節性上的變化呈現夏天高冬天低，在夏季其變化範圍大約為1.0~1.5meq/L，冬季時候鹼度明顯降低，其原因主要是受到酸雨的影響，雨水中的酸度中和了鹼度，此外，也會受到光合作用影響。最後則是探討整個淡水河流域內鹼度與河水中主要離子濃度的關係，以瞭解地質上或者是土地利用的不同對於河水中鹼度及主要離子的影響。在各主要離子中，以鈣與鹼度相關係數最高，但複迴歸分析顯示鹼度與鈣、鎂、鈉等離子有形成極佳之關係。在各支流中，大漢溪與主要離子間關係較差，R2在0.85左右，其他兩支流之R2都高於0.90。另外，三大支流的高程有明顯的不同，其中以大漢溪高程最高，在上游處裸土所佔比例較多，使得大漢溪鹼度為三條支流中最高。而裸土及農業用地越多、森林越少化學風化速率越快，使其鹼度值會變高，反之，鹼度則變低。

關鍵字

淡水河 ； 鹼度 ； 翡翠水庫 ； 桃園大圳

並列摘要

The Danshuei River in northern Taiwan has three major tributaries: Dahan Hsi, Shindien Hsi and Keelung River. The three watersheds have considerable differences in the natural conditions as well as human activities. The two reservoirs located in the drainage basins of the Danhan Hsi and Shindien Hsi are major water supplies to the population in the northern Taiwan. Consequently, the geochemistry of the Danshuei River water is closely related to the water quality of the regional water supply. The source of the alkalinity and major ions in the river water is mainly from weathering of the rock formation in the watershed. The water drains through the surface and groundwater ducts to reach the river channel. Therefore, research on the river water alkalinity can help us understand how the weathering processes may affect the water quality. Besides geochemical processes, the effects of biological activities and precipitation on the water quality were also examined. The relatively long residence time of reservoir water makes the biological effects quite evident. Precipitation in different seasons are from different air masses, which may give waters of different acidities, which in turn may have different effects on water quality. This study comprises three parts dealing with the Feitsui Reservoir, the Taoyuan Irrigation Ditch from the Shimen Reservoir and the whole Danshuei River watershed, respectively. Water samples were collected and filtered for determination of pH, alkalinity, and concentrations of major ions.
The Feitsui Reservoir displays significant biological effects on its water quality. For instance, photosynthesis causes increase of alkalinity, so does denitrification, whereas respiration decreases alkalinity. Different processes occurred in different layers of the stratified water column in different seasons. In the second part, it is shown that the water in the Taoyuan Irrigation Ditch was influenced by acid rains. The alkalinity was high in summer and low in winter. The range was from 1.0 to 1.5 meq/L in summer and decreased significantly in winter because of the neutralizing capacipty of the acid rains. In addition, it was also affected by photosynthesis. The third part explores the relationship between alkalinity and major ions in the Dahan, Hsindien and Keelung rivers. The regression analysis demonstrated a high correlation between calcium ion and alkalinity, while multiple regression using all major ions produced much better correlation. Amonmg the tributaries, the correlation coefficient of Dahan river is the lowest; its R2 is only 0.85; the others are higher than 0.90. The variations of chemical properties of river waters could be related to differences in land-use proportion as well as the elevation of the watershed. The high alkalinity of river waters from the Dahan Stream could be related to the higher elevation and higher percentage of bare soil. The agricultural use of land and bare soil may enhance chemical weathering, which may in turn contribute to the higher alkalinity. On the other hand, the forests appear to produce the lowest alkalinity.

並列關鍵字

Alkalinity ； pH

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