Seasonal variation of cyanobacteria and microcystins in the Nui Coc Reservoir, Northern Vietnam

Abstract

In order to understand the environmental varia- bles which promote the proliferation of cyanobacteria and variation in microcystin concentrations in the Nui Coc res- ervoir, Vietnam, physicochemical parameters, the occur- rence, and abundance of phytoplankton, cyanobacteria, and microcystin concentration were monitored monthly through the year 2009-2010. The relationships between these parameters were explored using principal component analysis (PCA) and Pearson correlation analysis. The phy- toplankton community was mainly dominated by the cya- nobacterium Microcystis with higher cyanobacteria abundance during summer and autumn season. PCA and Pearson correlation results showed that water temperature and phosphate concentration were the most important vari- ables accounting for cyanobacteria, Microcystis, and micro- cystin occurrence. Analysis of the toxins by high- performance liquid chromatography demonstrated the pres- ence of two microcystin variants: microcystin-LR (MC-RR) and microcystin-ddRR (MC-ddRR) with total concentra- tions of the toxins in filtered samples from surface water ranging from 0.11 to 1.52 μg MC-LR equiv L �1 . The high concentrations of microcystin in the Nui Coc reservoir high- lighted the potential risk for human health in the basin. Our study underlined the need for regular monitoring of cyano- bacteria and toxins in lakes and reservoirs, which are used for drinking water supplies, not only in Vietnam but also in tropical countries.