Abstract
The quantitative analysis of self-purification process related to phytoplankton and zooplankton in eutrophicated water is investigated. From microcosm experiments, following results are obtained :
(1) The first reaction of organic decomposition in eutrophicated water is the endogenous respiration by phytoplankton, and then the bacterial decomposition gradually occurs. Zooplankton promotes bacterial activity.
(2) The degradation process of particulate materials is expressed with first order reaction, and the rate constants range from 0.02 to 0.07 d-1. Following this reaction, nutrients are released into water, but the release of phosphorus is sometimes delayed, especially at a low temperature, such as 10°C.
(3) The oxygen consumption rate can be approximately expressed with the sum of the respiration rates of three organism groups : bacteria, phytoplankton and zooplankton. Phytoplankton's respiration rate Rp (mgO2·l-1·hr-1) can be estimated with the photosynthesis rate Pr (mgO2·l-1·hr-1) by the equation Rp=k * Pr, where k is ranging from 0.05 to 0.3, depending on algal species.
(4) Water temperature has an influence on reaction rate of each process with the thermal effect coefficients of 1.051.10 on COD, 1.091.14 on N and 1.091.26 on P.
