夢幻湖生態保護區土壤性質與水分運動過程對臺灣水韭棲地影響

Soil Texture and Water Processes for Analyzing Habitat of Isoetes taiwanensis in Menghuan Pond

許耀文(Yao-Wen Hsu)

指導教授 ： 施上粟

國立臺灣大學/工學院/土木工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202002017

摘要

夢幻湖生態保護區位於陽明山國家公園境內，水域面積隨季節改變，介於0至0.3公頃，為一內陸濕地。湖內有珍稀植物臺灣水韭族群（Isoetes taiwanensis DeVol），屬沉水性至短暫濕地生蕨類植物。
　　臺灣水韭具耐旱能力，能夠短暫適應湖區於長期無降雨時面臨的乾涸期，使其族群能夠持續生存於湖區中，並為其與其他植生族群競爭主要關鍵。本研究目的為根據土壤及水文條件劃設夢幻湖重點管理區域，並提出臺灣水韭於乾涸時含水量指標，作為量化評估基準及經營管理參考。本研究假設湖區底質土壤本身的保水能力為臺灣水韭當前能於夢幻湖維持穩定族群的主要因子之一，並進行現地調查及試驗室實驗進行假說驗證。
　　本研究藉由現地試驗與室內試驗，調查土壤的基本性質、滲透性與有機質含量，並建立無降雨水文收支模型，評估量測資料的高估或低估趨勢。
　　根據調查結果，湖區內土壤有機質比例接近30%，分類屬泥炭土。土壤重量含水量介於1.05至1.38間；孔隙率介於0.73至0.75間。水分持留曲線之結果顯示，田間含水量約為0.4至0.65；殘餘含水量則低於0.24至0.40。滲透性方面，飽和水力傳導係數介於1.30E-06至5.89E-08 m/s間；入滲率與滲流計流出速度數量級皆屬E-07 m/s。根據無降雨水文收支模型，於短時間長度時，滲流量與理論流失量的比值約介於0.89至1.69間；而當模型中的水位起終與短時間長度之事件相似，但時間長度增加，使用全時間相同的入滲量與滲流量將略高估理論流失量，比值介於1.39至2.40間。
　　以上結果顯示夢幻湖的土壤整體保水能力佳，此濕地土壤於雨季時降低地表水的流失至地下水之速度，乾季時則提供臺灣水韭的棲地保水土層。夢幻湖的土壤具有空間異質特性，南區的土壤組成偏砂質，滲透性較高，其他區域則皆為典型之泥炭土。若比對前人的植生調查結果，可發現滲透性較低的中區與北區，臺灣水韭覆蓋率較高，此亦表示保水土層的存在有助於臺灣水韭的競爭，提供其優勢棲地條件，保水能力研判與臺灣水韭的地下部及其種子庫的健康程度有關。

關鍵字

高山濕地 ； 臺灣水韭 ； 保水能力 ； 滲透性

並列摘要

Menghuan Pond Ecological Protected Area locates at Yangmingshan National Park, Taipei, which is an inland mountain wetland. The water area of Menghuan Pond would change in different seasons, and the range is about 0 to 0.3 hectares. Menghuan Pond is the only natural habitat of the endemic aquatic fern species, Isoetes taiwanensis DeVol.
I. taiwanensis could live in a drought period shortly, and even there was no water in the wetland. This adaptation was the critical point to maintain its population between other aquatic species. The purpose of this research is to put forward the evaluation standard of habitat management of I. taiwanensis by investigating the soil properties and hydrological conditions. The research assumed that the water retention capacity of the soil was one of the main factors to maintain the population of I. taiwanensis. A series of field investigations and laboratory tests were set up to validate the assumption above. Based on the results above, the “no-precipitation water budget model” was built to evaluate the precision of the investigation results.
The gravimetric water content was between 1.05 to 1.38; porosity was between 0.73 to 0.75. The field capacity and residual water content from water retention curve were 0.4 to 0.65 and 0.24 to 0.40, separately. In the aspect of permeability, the hydraulic conductivity was between 1.30E-06 to 5.89E-08 m/s; the infiltration and seepage rate were all in E-07 m/s order. The proportion of organic matter in the soil was almost 30%, which could be classified as “peat material”. On the other hand, the no-precipitation water budget model showed that the ratio of measured outflow amount to the ideal outlet was 0.89 to 1.69 in hour scale, and the ratio increased to 1.39 to 2.40 in one-day scale. The ratio that larger than 1 indicated the measured outflow rate was over-estimated.
The results showed that the soil in Menghuan Pond had excellent water retention capacity. The soil could lower down the loss of surface water in the rainy season, and become the water retention layer in the dry season. Also, the soil in Menghuan Pond had spatial heterogeneity from the investigation results. The soil in the southern area had sand material in soil texture, which caused the better permeability; the soil in the central and northern areas were typical peat material. Compared with the vegetation investigation, the lower permeability area had higher coverage of I. taiwanensis, which also indicated the existence of a water retention layer was helpful to I. taiwanensis to compete with other vegetation.

並列關鍵字

Mountain wetland ； I. taiwanensis ； Permeability ； Water retention capacity

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