Sixty-five percent of Taiwan’s reservoirs were eutrophic during a water shortage last year, the Environmental Protection Administration (EPA) said this week.
Eutrophication affected 35 of Taiwan’s 55 reservoirs last year, while the oligotrophic Feitsui Reservoir (翡翠水庫), which supplies the Taipei metropolitan area, had the best water quality, the EPA said.
Eutrophication is caused by an excess of nutrients, which results in a buildup of plant life that limits the benefits of light and oxygen in water.
Photo: Lin Ching-hua, Taipei Times
Mesotrophic water contains a moderate amount of nutrients, encouraging the growth of submerged aquatic plants, while oligotrophic water is clear and of higher quality.
The EPA regularly analyzes water samples from reservoirs, including 20 major reservoirs and six minor ones on Taiwan proper, and 26 on outlying islands. It monitors the water quality of key reservoirs monthly and general reservoirs quarterly.
Eight major reservoirs on Taiwan proper were eutrophic — Shihmen Reservoir (石門水庫) in Taoyuan, Baoshan Reservoir (寶山水庫) in Hsinchu County, Mingde (明德水庫) and Liyutan (鯉魚潭水庫) reservoirs in Miaoli County, Baihe (白河水庫) and Jingmian (鏡面水庫) reservoirs in Tainan, and Chengching Lake (澄清湖水庫) and Fengshan Reservoir (鳳山水庫) in Kaohsiung — while 11 reservoirs were mesotrophic, the EPA said, citing its water quality report for last year.
Among the six minor reservoirs on Taiwan proper, Dapu Reservoir (大埔水庫) in Hsinchu County, Toushe Reservoir (頭社水庫) in Nantou County and Agongdian Reservoir (阿公店水庫) in Kaohsiung were eutrophic, while the other three were mesotrophic, the report said.
All of the reservoirs on the outlying islands were affected by eutrophication, it said.
Hou Chia-hung (侯嘉洪), a professor at National Taiwan University’s (NTU) Graduate Institute of Environmental Engineering, on Monday said that precipitation levels can affect a reservoir’s water quality.
If there is not much rain, an excess of nutrients such as nitrogen and phosphorous stimulates algal growth, a phenomenon called “algal bloom,” Hou said.
Eutrophication causes concern, as algae can produce toxins that might be harmful to human health, although algae can be completely removed in water treatment processes, he said.
However, eutrophication makes tap water more difficult to process, especially when it comes to deciding how much algae remover is needed, he said.
Taiwan Water Resources Protection Union director Jennifer Nien (粘麗玉) said that last year’s shortages almost dried up some reservoirs and caused serious algal blooms.
Due to eutrophication, water purification plants would add more chemicals to water to remove the algae, Nien said.
EPA Office of Water Quality Protection head Yen Hsu-ming (顏旭明) said that eutrophication is evaluated using the Carlson trophic state index, which is determined by the level of suspended chlorophyll-a solids and the transparency of the water.
If the chlorophyll-a levels are too high, it can be inferred that eutrophication is due to an algal bloom, which can be resolved by removing the algae, Yen said.
However, if the eutrophication is caused by “reservoir killer” microcystis, ingesting the water might cause acute gastroenteritis, dermatitis, hepatitis or cancer, he said.
However, the possibility of contracting such diseases from drinking tap water is low and the EPA checks water quality regularly to ensure it is safe, he said.
The EPA tests water before and after it is treated, he said.
Lin Yi-pin (林逸彬), a professor at NTU’s Graduate Institute of Environmental Engineering, said that people should not worry too much about water quality, as it is carefully monitored at multiple stages.
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