Seasonal variation and indirect monitoring of microcystin concentrations in Daechung Reservoir, Korea

Physicochemical and biological water quality, including the microcystin con centration, was investigated from spring to autumn 1999 in the Daechung Res ervoir, Korea, The dominant genus in the cyanobacterial blooming season was Microcystis. The microcystin concentration in particulate form increased d ramatically from August up to a level of 200 ng liter(-1) in early October and thereafter tended to decrease. The microcystin concentration in dissolv ed form was about 28% of that of the particulate form. The microcystins det ected using a protein phosphatase (PP) inhibition assay were highly correla ted with those microcystins detected by a high-performance liquid chromatog raph (r = 0.973; P < 0.01). Therefore, the effectiveness of a PP inhibition assay for microcystin detection in a high number of water samples was conf irmed as easy, quick, and convenient. The microcystin concentration was hig hly correlated with the phytoplankton number (r = 0.650; P < 0.01) and chlo rophyll-a concentration (r 0.591; P < 0.01). When the microcystin concentra tion exceeded about 100 ng liter(-1), the ratio of particulate to dissolved total nitrogen (TN) or total phosphorus (TP) converged at a value of 0,6. Furthermore, the microcystin concentration was lower than 50 ng liter(-1) a t a particulate N/P ratio below 8, whereas the microcystin concentration va ried quite substantially from 50 to 240 ng liter(-1) at a particulate N/P r atio of >8. Therefore, it seems that the microcystin concentration in water can be estimated and indirectly monitored by analyzing the following: the phytoplankton number and chlorophyll-a concentration, the ratio of the part iculate and the dissolved forms of N and P, and the particulate N/P ratio w hen the dominant genus is toxigenic Microcystis.