The water at four reservoirs in southern Taiwan has suffered eutrophication and needs to be improved, the latest report by the Environmental Protection Administration (EPA) on the water quality of 20 reservoirs last year showed.
Water quality is evaluated each season using the Carlson trophic state index (CTSI), an index that considers the transparency, the chlorophyll-a concentration and the phosphorus concentration in a body of water, said Chen Chih-ming (陳志銘), a section chief at the EPA’s Department of Water Quality Protection.
The water is considered “oligotrophic” (good quality) when the index is lower than 40, “mesotrophic” (normal quality) when the index ranges between 40 and 50, and “eutrophic” (bad quality) when the index is above 50, making the water inadequate for household use, Chen said.
Department of Water Quality Protection Director Hsu Yung-hsing (許永興) said the four reservoirs with poor water quality last year were Greater Kaohsiung’s Fongshan Reservoir (鳳山水庫), with a CTSI of 73.3, the Agongdian Reservoir (阿公店水庫), with a CTSI of 53.4, Chengching Lake (澄清湖水庫), with a CTSI of 52.7, and Greater Tainan’s Ching-Mien Reservoir (鏡面水庫), with a CTSI of 50.3.
Of the four reservoirs, the water at the Agongdian Reservoir is only used for industry and it does not threaten households.
Other than the four eutrophic reservoirs, 12 were evaluated as mesotrophic and four as oligotrophic, Hsu said, adding that the average water quality of the nation’s reservoirs has steadily improved in the last decade.
However, data from the EPA showed that the CTSI at 11 reservoirs deteriorated last year.
Chen attributed the change to increased levels of nutrients such as nitrates and phosphorus in the water, causing a substantial increase of phytoplankton.
The increase of nutrients may come from multiple sources, including wastewater from stockbreeding, farming, household waste, industrial waste and even soil erosion, as well as the growth of algae affected by the temperature, he said.
Hsu said the water at the Chengching Lake was mainly affected by dredging upstream, while the Agongdian Reservoir was affected by agricultural and household waste upstream. The Ching-Mien Reservoir was affected by landslides upstream and the Fongshan Reservoir by stockbreeding, also upstream.
The EPA said it would continue to monitor water quality and provide funding to local environmental protection agencies to execute pollution cutback programs, such as instructing farmers on better fertilizer solutions.