Abstract
Seasonal changes in the vertical profile of chlorophyll-a, CODMn and nutrient concentrations in an agricultural irrigation reservoir were investigated for two years. The reservoir had a maximum depth of 9 m, a surface area of 1.2 × 105 m2 and a maximum storage volume of 5.6 × 105 m3. The hydraulic retention time was about 3 days from April to August, and was 7 days from September to March. In July, Volvox sp. were dominant when the retention time was less and nutrient supply rates were high. On the other hand, Microcystis sp. were dominant when the retention time was more and nutrient supply rates were low in September. These results coincided partly with the occurrence of cyanobacteria blooms in nutrient-rich and slow-flowing waters.
