Abstract
Eutrophication in reservoirs is principally caused by phytoplankton. It is generally thought that the problem of eutrophication worsens when the water detain for long periods of time. However, recent observational studies show that the prolongation of retention time does not always increase quantities of phytoplankton.In this paper, the results of a series of experiments done to find the relationship between retention time and phytoplankton abundance, is presented. The continuous culture method, which has been a popular technique used for microbe cultures, was utilized to grow phytoplankton in this study. It has been found that, under the supply of nutrients with constant concentration, the abundance of phytoplankton in the incubator changes with retention time. However, the amount of phytoplankton increases with a retention time only initially, and further retention causes the concentration to drop. Hence, there seems to be an 'optimum' retention time at which the phytoplankton abundance reaches a peak value.
