| Summary: | 碩士 === 國立臺灣大學 === 環境工程學研究所 === 102 === Reservoirs in Kinmen are shallow and in-channel reservoirs, and most of them are under eutrophic condition. Reservoirs provide 42 % of the water sources for water treatment plants in Kinmen. The fraction of raw water drawn from reservoirs has been reduced in recent years due to the deterioration of water quality, which lowered the production rate of water treatment plants. Particularly, the high dissolved organic carbon (DOC) in most of the reservoirs is high potential of disinfection byproducts in drinking water, which pose risk of cancer to public and increase the cost for water treatment. Therefore, it is the aim of this study to investigate the change of water quality, the formation of high organic matter, and the possible improving approaches. Rong-hu reservoir and Jin-sha reservoir are the two studied reservoirs.
The results of continuous monitoring of temperature profiles in these two reservoirs indicate that stratification was formed in summer, which led to an anaerobic condition at the bottom of the water column and increased the amount of internal nutrient loading. The stratification was easily broken by strong wind, heavy rainfall and low air temperature. And the turnover occurred quite early in September, which well mixed the water body. The results of water quality investigation showed that the nutrients in reservoirs were imported by run-offs containing high concentration of nutrient. Blue-green algae dominated in the two reservoirs for the whole year, except in July 2013 in the two reservoirs and February 2014 in Jin-sha reservoir. Cylindrospermopsis rociborskii, one of the blue-green algae, outgrew all other algal species in most of time by taking the advantages of low N/P, well-mixing water body, and suppressing other algae by secreting extracellular polymeric substances.
DOCs in the reservoirs were from watersheds and internal sources, sediment and algal exudates. The results of stable isotope carbon ratio analyses showed that DOC in reservoir was mainly produced by algae. In winter and spring, vigorous competition among phytoplanktons induced large amount of algal secretion which formed DOC in water.
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