夢幻湖水生植物競爭之生態水文模式建立及應用

Development and Application of an Eco-hydrological Model for Competitive Aquatic Plants in Menghuan Pond wetland

李冠穎(Kuan-Ying Lee)

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(2021年)

https://doi.org/10.6342/NTU202101000

摘要

陽明山夢幻湖生態保護區為臺灣水韭（Isoetes taiwanensis De Vol）自然棲地，具有重要生態保育價值。過去研究發現若發生長時間水位過低甚至乾涸等極端水文條件，將改變植物之間的競爭態勢，臺灣水韭的數量會因此急遽減少。此外，湖區內部具有兩處已知裂隙，東南方山壁上具有一長時間出流的裂隙，可能是造成湖水快速流失的主因，但夢幻湖的湖水與地下水機制的研究非常缺乏，因此在評估本區生態保育狀況時，較難有全盤性的掌握。有鑒於此，本研究透過資料收集、現地調查、模式建立的方式，綜整分析夢幻湖之地面水、地下水與裂隙之間的交互作用機制，瞭解湖水位下可能的流失方向與途徑，並建立快速且準確的地下水位預測模式提供未來水位控管的依據，搭配臺灣水韭於不同區位的優勢程度與臺灣水韭棲地指數，即可完整監測夢幻湖在水與植物上的變動情形。本研究之主要發現整理如下：
（1）地面水、地下水與裂隙關係：透過設立於湖區內的湖水位、地下水位觀測井輔以示蹤劑試驗，建立夢幻湖地面水、地下水與裂隙交互作用概念模型；另外利用地下水位觀測井進行圖像化的地下水流向分析，以玫瑰圖探討其可能的流失方向，發現地下水流向不會直接穿越湖區，而南區是地下水主要流失路徑及熱點。透過乾、溼季湖水位與地下水位超越機率曲線，於適當的假設之下，只要取得當下的湖水位資料，查閱其超越機率並對應到相同機率的地下水位，即是當下的地下水位預測值，正確率於乾季達90.54%、溼季達94.14%。
（2）湖區內水生植物競爭態勢：導入水深超越機率曲線與植物生長的相關參數，分析夢幻湖五種優勢植物不同區位、不同季節的優勢情形。分析結果顯示，柳葉箬(Isachne globosa)、荸薺(Eleocharis dulcis)、針藺(Eleocharis congesta)、水毛花(Schoenoplectus mucronatus)等四種植物於非浚深區可取得競爭上的優勢；浚深區因能提供較深的平均水深，臺灣水韭在此區較有競爭上的優勢。
（3）臺灣水韭棲地指數模式：本研究透過自建的棲地指數，分析臺灣水韭不同區位、不同季節的指數，之後加入覆蓋度進行二次曲線函數的擬合，得到指數值0.146時，可得擬合後的覆蓋度最大值74.66%。指數值0.025與0.266為此函數覆蓋度為零的臨界點。目前臺灣水韭雖覆蓋度隨季節變動，但與臨界點仍有段差距，推測夢幻湖當前環境仍可供臺灣水韭生存。

關鍵字

臺灣水韭 ； 交互作用概念模型 ； 玫瑰圖 ； 超越機率 ； 棲地指數

並列摘要

Menghuan Pond Ecological Protected Area is located at Yangming Mountain, which is the natural habitat of Isoetes taiwanensis De Vol. The wetland is vital and needs ecological conservation. According to some research, if extreme hydrological events, such as low water levels or drought periods, will change the competitive situation among aquatic plants in the wetland. As a result, the number of I. taiwanensis would decrease rapidly in Menghuan Pond. Furthermore, there are two cracks in the wetland and one crack located at the southeastern cliff. It was suspected that they resulted in water loss of the wetland. However, little research discusses the mechanism between surface water and groundwater in Menghuan Pond. Thus, it was hard to evaluate the conservation status in the wetland comprehensively. In light of this, the research investigated the mechanism among surface water, groundwater, and cracks. Therefore, we could reveal groundwater flow directions and their ways of loss at different water levels. Also, this research built up the predictive model of groundwater level with high precision and real-time. It is feasible to thoroughly monitor the state of Menghuan Pond by combining the groundwater model with the values of the habitat index of I. taiwanensis. The following are the significant findings of this research.
Relation among surface water, groundwater, and cracks: the researchers used water level records, groundwater level records, and tracer tests to build up the conceptual model of Menghuan Pond. Besides, groundwater level records were used to analyze groundwater flow directions as well. We introduced the concept of rose diagrams to visualize groundwater flow directions and their ways of loss. Furthermore, it is feasible to employ the exceedance probability in estimating a groundwater level value under the appropriate assumption. Hence, if we got a water level value, the corresponding groundwater level value at the same exceedance probability would be the groundwater level value at the same time in Menghuan Pond. The accuracies of the dry season and the wet season were 90.54% and 94.14%, respectively.
Competition of aquatic plants: the research analyzed five species of aquatic plants in different seasons and at different areas in Menghuan Pond by combining the exceedance probability of the water depth with parameters of aquatic plants. The results showed that Isachne globosa, Eleocharis dulcis, Eleocharis congesta and Schoenoplectus mucronatus were dominant plants in the non-dredging area. Because of the deeper water depth, I. taiwanensis was more competitive at the dredging area than at the non-dredging place.
Habitat index model of Isoetes taiwanensis: the habitat index is the new concept defined by this research, which tries to figure out different indices of I. taiwanensis in different seasons and at different zones in Menghuan Pond. The fitting function of the area (%) in sample plots and the habitat index of I. taiwanensis was a quadratic equation. The minimum of the equation was zero when the values of the habitat index of I. taiwanensis were 0.025 and 0.266. The maximum of the equation was 74.66% when the value of the habitat index of I. taiwanensis was 0.146. The results showed that I. taiwanensis were still competitive in Menghuan Pond.

並列關鍵字

I. taiwanensis ； conceptual model ； rose diagram ； exceedance probability ； habitat index

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