博士 / 國立臺灣大學 / 環境工程學研究所 / 101 / Eutrophication is the most common cause of water-quality problems; in subtropical regions while the eutrophic conditions caused by cyanobacteria are particularly of most concern. Several cyanobacterial species release toxins and most species excrete dissolved organic matters which are the precursors of disinfection by-products (DBP). Microcystis is the most common bloom-forming genus of toxic cyanobacteria in Taiwan, which is also the dominating species in Hsin-shan Reservoir in recent years (Wu et al., 2010). Taiwan EPA has investigated 11 eutrophic reservoirs in 2005. Microcystis has appeared in all of those reservoirs (Kuo et al., 2005). Hence, Microcystis bloom is the most concerned and urgent problem.
In this thesis, Hsin-shan Reservoir is the reservoir studied to investigated the Microcystis seasonal succession. The temporal and spatial field data including Microcystis concentration (cells/L) over depth, water quality parameters over depth and climate records from 2005 to 2009 were collected. At the beginning, relationships between Microcystis succession and environmental factors were be identified with statistic approaches. Then, a model was developed to simulate the dynamic change of Microcystis population by using a trajectory approach, in which the ability of diurnal migration due to density change and growth rate caused by cell quota were taken into consideration. Better understanding on the relationship between the environmental factors and Microcystis successtion was obtained through the model simulation.
It was found that the abundance of Microcystis had positive correlation with water stability. There is no relationship among water parameters while water body was well mixing. Microcystis abundance and most water parameters vary over depth under stratified and transition stages. A trajectory approach was used to simulate the diurnal migration and succession of Microcystis, for the purposes of considering the stratified environment and the special growth behavior of Microcystis. This developed model is better than an advection-diffusion model for being able to reflect the migration and growth pattern of Microcystis, by recording all histories of surrounding light intensity, nutrient, and other environmental factors which each individual colony has experienced. The results of the simulation show that there exists an optimum distribution of Microcystis colonies which enable Microcystis obtain dominance in stratified water bodies. Smaller colonies are dragged by turbulent force and dispersed randomly over the mixing zone; whereas larger colonies obtain advantages byovercoming turbulent diffusion and getting higher frequency of cyclical shifts between the euphotic zone and the nutrient-rich deeper water layers. However, when taking the mechanism of the growth and that of nutrient-uptaking into consideration, the colonies with diameters larger than 500 μm will not gain dominance due to staying surface layer too longer to get enough nutrient. The results of the simulation are coincident with the field observation of the vertical profile of Microcystis concentration.
Furthermore, the effect of intake elevation on the Microcystis growth by the simulation of two intaking scenarios, inflow from surface or flow from bottom was investigated. The results of simulation show the operation by intaking from bottom was able to separate light and nutrient and suppress the growth of algae. The results suggest a solution for controlling Microcystis growth in a stratified reservoir.
The results of the investigation of the effect of reducing available light intensity by artificial mixing of water within 10 meters from surface showed that the total algal concentration become higher and the dominating species had changed. Although the abundance of Microcystis was reduced significantly, phytoplanktons with competitive ability of survival at lower light intensity had dominated due to that nutrients might be transported into the epilimnion by mixing. It will be easy to expand the trajectory model into multi-species succession models in the future, and the field data of operating and artificial mixing could be used to verify the model of the multi-species succession.
| Identifer | oai:union.ndltd.org:TW/101NTU05515001 |
| Date | January 2013 |
| Creators | Yu-ching Chien, 簡鈺晴 |
| Contributors | Shian-chee Wu, 吳先琪 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 171 |
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