磺港溪與南磺溪水體之稀土族元素特性研究

Hydrochemical Study of Huanggang Creek and South Huangg Creek Using Rare Earth Elements as a Natural Tracer

蕭宇翔(YU-HSIANG HSIAO)

指導教授 ： 呂學諭

國立中正大學/理學院/地球與環境科學系應用地球物理與環境科學研究所/碩士(2015年)

摘要

南磺溪及磺港溪上游來源為大屯火山地區，磺港溪流經北投至關渡平原，兩溪皆受到溫泉的補注，根據陰離子分析及質譜儀分析，磺港溪在支流處受到地熱谷溫泉的補注進而影響磺港溪下游水質，此外，地熱谷溫泉具有高濃度的砷汙染，因此一般認為地熱谷溫泉為關渡平原砷汙染的來源；南磺溪在下游則受到龍鳳谷溫泉之補注，而不受到砷的汙染。稀土元素的示蹤結果顯示，磺港溪支流之地熱谷溫泉水較不具有沉積岩的訊號，在安山岩正規化的結果中展現其輕稀土更為貧乏的現象，可能代表溫泉水有深層的火成訊號來源，然而隨著溫泉混染至上游，開始出現沉積岩訊號，砷汙染隨之降低，以沉積岩訊號較強之龍鳳谷溫泉與之相比，反而未顯現出砷汙染自沉積岩中溶出之結果，因此推測砷汙染之來源可能由溫泉自地層深部攜出，而非來自於沉積岩溶出之結果。根據氯離子受到溫泉蒸氣逸散而濃縮的機制，可以更合理的解釋地熱谷之溫泉水其氯離子濃度極高，而蒸氣冷凝所形成之的硫磺谷及龍鳳谷溫泉水不具有高氯濃度的現象。
熱力學模擬軟體PHREEQC之結果清楚表示磺港溪水體的砷汙染受到HFO共沉澱的因素所控制，計算HFO之飽和指數後發現當pH值大於2.7則HFO開始移除水中的砷，然而此作用受到反應速率的影響，導致砷的移除作用在分析結果上並不顯著。

關鍵字

陽明山 ； 南磺溪 ； 磺港溪 ； 稀土元素 ； 溫泉

並列摘要

Two major rivers, Huanggang Creek and South Huang Greek, flow through Guandu Plain. Both creeks originate from Tatung Volcano Group, which is extensively active in post-volcanic activities. In this study, the hydrochemistry along the two major rivers was studied for tracing the source of springs by REEs. According to the chemical analysis, the branch of Huaggang Creek is recharged by the spring of Thermal Valley which was highly arsenic-contaminated. Without arsenic contamination, South Huang Creek is recharged by the spring of Longfong Valley. In Huanggang Creek, A3-nomoralized REE patterns show an extremely LREE-depleted type without sediments signals at HK03 but little sediments signals in the upstream. Sample in the downstream of South Huang Creek give the REE patterns with sediments signals. It can be concluded that the arsenic pollutions was not dissolved from sediments but carried in from deep stratum by Thermal Valley spring instead. In addition, high concentration of chloride could be not due to dissolution of HCl gas but due to steam loss, while the spring was raised up.
The results of thermodynamic modeling demonstrate that SI of HFO is mainly controlled by pH in this study. When pH is greater than 2.7, HFO start to precipitate and remove arsenic from water. Therefore, it is believed that the arsenic pollution in Guandu Wetland could result from HFO co-precipitation due to the increase of pH when Huanggang Creek flow through the land.

並列關鍵字

rare earth elements ； spring

參考文獻

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