淡水河水筆仔胎生苗移流及延散特性研究

Advection and Dispersion Characteristics of Mangrove Propagule Dispersal with Kandelia obovata in Tanshui River

許偉斌(Wei-Bin Xu)

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/NTU202003507

摘要

本研究透過現場調查、水槽試驗及建立數值模式的方式，分析紅樹林種源的移流延散特性。以淡水河系4個水筆仔紅樹林主要生育地為研究對象，包括：挖子尾、竹圍、關渡、社子，進行胎生苗現地採樣、調查，後於實驗室內進行相關形態參數統計、分析。並在不同鹽度條件下完成了為期60天的胎生苗生理試驗及觀測。同時，藉助水槽試驗及影像追蹤測量技術對胎生苗移流、延散特性加以研究，並與PTM（Particle Tracking Model）粒子追蹤模式的模擬結果比對、分析，以此率定胎生苗於PTM中重要的水平紊動擴散係數經驗係數KEt。
重點研究成果如下：1. 胎生苗形態參數調查發現，4個水筆仔紅樹林生育地的胎生苗形態參數都基本服從常態分配；且胎生苗平均密度接近於1.0，與水的密度相近，使之能夠漂浮。2. 生理試驗及觀測結果表明，在不同鹽度條件下，胎生苗的質量變化率平均值Pm為1.81×10^(-3)/day，體積變化率平均值Pv為-1.602×10^(-4)/day，說明胎生苗在移流、延散的漂浮過程中質量、體積及密度的變化均不明顯。3. 結合胎生苗水平紊動擴散係數經驗係數KEt的率定成果，將KEt取值定為0.05，合理設定了胎生苗在PTM模式中的延散參數。4. 將影像追蹤測量水槽試驗中胎生苗的移流、延散成果與PTM模式追蹤胎生苗粒子的成果比對，可知兩者胎生苗的橫縱向位移比均較小，在移流過程中縱向位移更為重要。兩者縱向移流平均速度與實際流場有關，較接近流場垂線平均流速，但真實水槽中粒子移流平均速度較PTM模擬值為大。5. PTM模式模擬粒子移動軌跡的橫向平均位置較準確，而對於縱向移流平均速度、縱向移流平均時間及橫向位置標準差的模擬存在一定誤差，但在實際案例的PTM模擬中這些誤差均可被合理忽略，說明PTM模式能夠較好地應用於現地紅樹林胎生苗種源擴散趨勢的預測及分析。
基於前述基礎研究成果並結合淡水河系現地的流量水位、地形調查成果，建置淡水河系SRH-2D水動力模式，模擬了淡水河系水理狀況。再以該水理狀況作為PTM數值模式的水動力條件，進而模擬、分析淡水河系4個紅樹林濕地的種源移流及擴散能力，並評估彼此間種源交換的可能情形。結果發現:關渡濕地所釋放胎生苗粒子在河道中移流、擴散的輸移時長最長，而社子濕地所釋放胎生苗粒子在河道中移流、擴散的輸移時長最短。挖子尾濕地所釋放胎生苗粒子移流、擴散能力最小，而竹圍、關渡、社子各自所釋放的胎生苗粒子移流、擴散能力基本相近。挖子尾濕地釋放的種源胎生苗基本只在挖子尾區域附近移流、擴散，極少往淡水河上游上溯，大部分均往外海傳播、擴散。而竹圍、關渡、社子所釋放的種源胎生苗均具備往上游上溯及向下游河口、外海傳播擴散的能力。竹圍、關渡、社子三者濕地间較易發生種源交換，而挖子尾與其他三個濕地間較難發生種源交換。
本研究提供了紅樹林種源移流、擴散趨勢預測機制建構的標準流程及方法，有助於建立紅樹林濕地生態系統復育及經營管理的科學基礎。

關鍵字

淡水河 ； 紅樹林 ； 水筆仔 ； 胎生苗 ； 種源擴散 ； 數值模擬

並列摘要

In our study, the advection and dispersion characteristics of mangrove propagule dispersal was analyzed with field investigation, flume experiment and numerical modeling. Four major mangrove habitats, Wazwei, Zhuwei, Guandu, and Shezi in Tanshui River, were selected for field investigation of Kandelia obovata propagules. The related geometric parameters of propagules were measured and recorded, as well as the conduction of physiological experiments lasting about 60 days. At the same time, the characteristics of advection and dispersion of propagule dispersal was studied performing a flume experiment and using image tracking and measurement technology, and we compared the characteristic results with the Particle Tracking Model (PTM) simulation results to calibrate the vital model parameter KEt.
The vital results of those preceding studies are as follows: 1. The investigations and statistics of the geometric parameters of propagules found that geometric parameters of Kandelia obovata propagules collected from the four mangrove habitats were subject to normal distribution; The density of propagules was about 1.0, which was close to that of water and was the reason why propagules can drift on the water surface and move with the flow. 2. Physiological experiments and observations showed that under different salinity conditions, averaged daily mass change rate Pm and daily volume change rate Pv of propagules were about 1.81×10^(-3)/day and -1.602×10^(-4)/day, indicating that mass, volume and density of propagules did not change significantly during their rafting process. 3. The calibration value of KEt was 0.05, meaning that the relevant dispersion parameter of propagules in PTM was reasonably set. 4. Through the comparison between the advection and dispersion characteristic results of propagule dispersal gotten from the flume experiment and PTM simulation, it can be known that the horizontal and longitudinal displacement ratios of propagule dispersal of both results were relatively small, and the longitudinal displacements of propagules were more significant relative to the longitudinal displacements during dispersal process. The average velocity of longitudinal dispersal of propagules in both were relevant to the actual flow field conditions, which were close to the 2D vertical average velocity of the flow field. However, the average velocity of longitudinal dispersal of propagules in the flume was more extensive than that of PTM simulation. 5. The PTM model had an excellent performance in the simulation of the horizontal average position of the propagule particle movement trajectory. There was certain simulation bias for the average velocity and time of longitudinal dispersal of propagules, besides the standard deviation of the horizontal position of propagules, while these bias can be reasonably ignored when PTM used in the actual case simulation, which indicates that the PTM model can be efficiently applied to the prediction and analysis of the actual trend of mangrove propagule dispersal in situ.
Based on the research mentioned above, and combined with the results of the in situ discharge, water level, and topographic survey of Tanshui River Basin, a hydrodynamic model SRH-2D of Tanshui River Basin was established to simulate the hydraulic conditions. The hydraulic results were incorporated into the PTM model to simulate further and analyze the characteristics of advection and dispersion of propagule dispersal and the exchange situation of propagules among the four mangrove wetlands. And it turned out that: The advection and dispersion duration in rivers of propagules released from Guandu was the longest, while that of propagules released from Shezi was the shortest. The dispersal ability of propagules released from Wazwei was the most limited, while that ability among propagules released from Zhuwei, Guandu and Shezi was basically similar. The advection and dispersion of propagules released from Wazwei almost exclusively occurred in its region, and the minority of propagules spread towards the upstream of the river, while the majority of propagules spread towards the downstream of the river, entering the ocean throughout the estuary. However, propagules released from Zhuwei, Guandu, and Shezi Wetland not only spread towards the upstream of the river but towards the estuary and ocean. Propagule exchange was more likely to occur among that three wetlands, Zhuwei, Guandu, and Shezi, while it was of little chance to occur between Wazwei and another three wetlands.
Our study provides standard procedures and methods for constructing a prediction mechanism for the trend of advection and dispersion of propagule dispersal, which is helpful in establishing a scientific foundation for mangrove wetland ecosystem restoration and management.

並列關鍵字

Tanshui River ； Mangroves ； Kandelia obovata ； Seedling propagules ； Propagule dispersal ； Numerical modeling

參考文獻

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