Eutrophication study of twenty reservoirs in Taiwan

Taiwan is an island off the southeastern coast of China with total area of roughly 36,000 km2. The geographic position of Taiwan is between 21degrees 45' 25" to 25 degrees 56' 31" north latitude and 119 degrees 18' 3"to 124 degrees 34' 30" east longitude and includes both tropical and subtropical areas. The study was carried out at twenty main reservoirs in Taiwan area from 1994 to 1998. The study revealed that the water quality of most reservoirs gradually deteriorated during the study period. Total phosphorus concentrations over 60 microg/L were observed in 12.5% of these reservoirs in 1994, but in 22.2% of these reservoirs in 1998. Total nitrogen concentrations over 1.0 mg/L were observed in 37.5% of these reservoirs in 1994, but in 94.4% of these reservoirs in 1998. Secchi disc transparency below 2 m was observed in 75% of these reservoirs in 1994, but in 83.3% of these reservoirs in 1998. Chlorophyll a concentrations over 15 mg/m3 were observed in 12.5% of these reservoirs in 1994, but in 27.8% of these reservoirs in 1998. The TN:TP mass ratios (wt/wt) of all the studied reservoirs except Akungting Reservoir, Fongshan Reservoir, and Chengching Reservoir are higher than 16. The study results on nutrient limitation indicated that phosphorus is the primary limiting nutrient in Taiwan reservoirs except Akungting Reservoir, Fongshan Reservoir, and Chengching Reservoir.