Most of the 26 reservoirs on Taiwan’s outlying islands are affected by eutrophication, while five out of the 20 category-one reservoirs on Taiwan proper are also affected by eutrophication, an Environmental Protection Administration (EPA) report showed.
Eutrophication is caused by an excess of nutrients, which results in a buildup of plant life that prevents light and oxygen from entering the water.
In April, the Mingde (明德), Baihe (白河), Jingmian (鏡面), Chengcing Lake (澄清湖) and Fengshan (鳳山) reservoirs were the five category-one reservoirs with the most eutrophication, the report said.
Photo: Wu Chun-feng, Taipei Times
The Fengshan reservoir scored 70 on Carlson’s trophic state index, the highest out of the five, the EPA said, adding that there are 14 mesotrophic reservoirs.
The Feitsui Reservoir (翡翠水庫), which provides water for the Taipei metropolitan area, has the best water quality, and is also considered oligotrophic, the report said.
Of the six category-two reservoirs, the Sishi (西勢), Dapu (大埔) and Agongdian (阿公店) reservoirs are considered eutrophic, while the remaining three are mesotrophic, it said.
As for reservoirs on outlying islands, only the Sian (西安) reservoir in Penghu County is mesotrophic, while the other 25 are eutrophic, it said.
Mesotrophic water contains a moderate amount of nutrients, encouraging the growth of submerged aquatic plants, while oligotrophic water is clear and of higher quality.
Speaking about the report on Friday, Hou Chia-hung (侯嘉洪), a professor at National Taiwan University’s (NTU) Graduate Institute of Environmental Engineering, said that precipitation levels can affect the water quality of reservoirs.
Decreasing water levels can cause a higher-than-normal concentration of nitrogen and phosphorus in the water, resulting in an algae bloom, he said.
It is suspected that toxins from algae can negatively affect human health, and as 70 percent of water for civilian use originates from reservoirs, eutrophication is placing an increased burden on water filtration systems, he said.
As eutrophication decreases the amount of oxygen in the water, it further unbalances the ecology, Hou added.
EPA Department of Environmental Monitoring and Information Management Director-General Chang Shuenn-chin (張順欽) said that the eutrophication of reservoirs on islands was caused by their small size and lack of water inflows to prevent stagnation.
A lack of rainfall, as well as bird feces, also contribute to the eutrophication of reservoirs, he added.
The eutrophication of the Fengshan Reservoir was caused by its water being diverted to other places, and due to the natural water quality of the Gaoping (高屏) and Donggang (東港) rivers, Chang said, adding that a lack of rainfall last year was also a factor.
Hou said that changing how the land around the reservoirs is used is key to stabilizing reservoir water supply.
“We still have a long way to go in terms of environmental conservation and decreasing sources of pollutants,” he said.
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