光線強度對微囊藻垂直移動之影響及模擬

Abstract

過去研究對於微囊藻在水體分層時大量生長之原因仍不瞭解，故無法預測其 優勢生長時機並提供良好之預防措施。本研究欲建立分析真實藻細胞密度之方法， 並以純藻培養及水庫現場藻細胞之兩組實驗，探討微囊藻細胞垂直移動之機制及 建立相關之軌跡模式。研究結果改善過去密度梯度液方法，將密度範圍擴大至小 於1 g/cm3。另外，本研究發展另一定密度溶液分析法，此方法較密度梯度液法更 適合用於水庫現場分析。純藻培養之實驗結果顯示，微囊藻細胞密度值皆小於一 般水體之密度範圍，此外，可能是由於長期培養於實驗室之微囊藻並不需要浮力 調控的機制即可生長，故微囊藻密度變化率與光線強度無明顯關係。水庫現場之 實驗結果顯示，微囊藻密度之變化率具有光抑制情形，包括光抑制效果之密度變 化關係式較為適用。本研究建立了微囊藻垂直移動之軌跡模式，並且可以不同初 始深度、藻團半徑、最大表水光線強度及基準係數，模擬微囊藻細胞上浮下沈之 現象。模式中加入了擴散作用之隨機位移項，部份模擬結果與水庫中微囊藻常以 團聚藻細胞存在之現象相呼應，顯示未來可以此軌跡模式為基礎，模擬及預測微 囊藻細胞在不同環境條件下之垂直移動。

The reason for the dominance of Microcystis in stratified water bodies found in previous studies is not clear. It is still difficult to predict when Microcystis will dominate or to provide a good preventive strategy without the understanding of the controlling factors of the growth of Microcystis. The purposes of study include establishing the methods for analysising the density of algal cells, better understanding the buoyant mechanism of Microcystis and establishing a trajectory model for the movement of the colonies of Microcystis based on the results of the pure-culture experiments and on-site experiments. The method of analysising the density of algal colonies was improved. The density range has been expanded to be lower than 1 g/cm3. This new method is ready to be used on site. The results of the pure-culture experiments in laboratory show that the density of Microcystis is much lower than that of freshwater and the density change rate has no obvious relationship with the irradiance intensity. It is believed that Microcystis which had been cultured in the laboratory for a long time might have lost the buoyance regulation mechanism. The results of the on-site experiments show photoinhibition. Photoinhibition was taken into consideration while establishing the relationship between the density change rate and irradiation intensity. The trajectory model established in this study is able to simulate the vertical migration of the colony of Microcystis at certain initial depth and colony sizes. The model is able to describe the diurnal movement of the algal cells in waterbodies under different environmental conditions. It is found that the bigger colony has more chance to overcome the separation of the light and the nutrient because it is less affected by diffusion. This trajectory model would be able to simulate the vertical movement and growth of algal colonies for longer duration precisely if the growth mechanism of nutrient uptake were added.