Environmental Factors Influencing Seasonal Variation of Microcystin-RR Concentrations in Baoyang River, a Shallow City River in Changxing of China

The shallow city river of Baoyang located in China had been eutrophicating with nutrients from domestic sewages for many years. A heavy bloom of Microcystis.aeruginosa in Baoyang River was recorded in 2004 and microcystin-RR (MCRR), the most popular cyanobacterial hepatotoxin microcystins in China, could be detected in the river in the next several years in the filtered waters. To determine the environmental variable factors associated with concentrations of MCRR, samples taken from the beginning of April 2008 to the end of March 2009, were analyzed by high-performance liquid chromatography with photodiode array detection. MCRR, the main microcystins found in the filtered water samples from spring to winter, ranged from undetectable to 4.37μg/L. The highest concentrations of MCRR were found in the late summer in October 2008, and the concentrations of MCRR at the bottom waters were higher than that at the aquatic surfaces. Significant positive relationships (p<;0.01) were observed between MCRR and NO₃-N; but significant negative relationships (p<;0.01) were observed between MCRR and pH, COD, NO₂-N and TN. This research indicated NO₃-N would be very important for the biosynthesis of MCRR. The relationships between MCRR concentrations and environmental factors were complicated and further researches should be focused on the prediction methods of microcystins by the nonlinear models for their potential health risks.