Effect of enclosure and nutrient enrichment on Microcystis blooms in Donghu Lake

A nutrient enrichment experiment was conducted in situ in Donghu Lake (30°33′N, 114°23′E), a shallow hypereutrophic lake in Hubei, China through an enclosure(each 2.5×2.5m by 2 m depth) method from July 15 to September 21, 2000. Three duplicated groups, including two treatments and one control, were designed as unfertilized control (C), nitrogen enrichment (N) and phosphorus en- richment (P), and were also compared with neighboring lake water. Dense Microcystis bloom exclusively dominated in all the enclosures, while no bloom was observed in the lake. All the enclosures had much higher phytoplankton biomass, higher pH values, and higher transparency than the surrounding lake water. Neither nitrogen nor phosphorus addition had significant effect on phytoplankton composition and bio- mass due to very high nutrient concentration in the lake water. Suitable biological (absence of fil- ter-feeding silver carp and bighead carp) and physical environment (high transparency, high stability and high pH) associate with saturated nutrient concentration contribute to the nuisance Microcystis bloom in the enclosures.

A nutrient enrichment experiment was conducted in situ in Donghu Lake （30°33′N, 114°23′E）, a shallow hypereutrophic lake in Hubei, China through an enclosure（each 2.5×2.5m by 2 m depth） method from July 15 to September 21, 2000. Three duplicated groups, including two treatments and one control, were designed as unfertilized control （C）, nitrogen enrichment （N） and phosphorus enrichment （P）, and were also compared with neighboring lake water. Dense Microcystis bloom exclusively dominated in all the enclosures, while no bloom was observed in the lake. All the enclosures had much higher phytoplankton biomass, higher pH values, and higher transparency than the surrounding lake water Neither nitrogen nor phosphorus addition had significant effect on phytoplankton composition and biomass due to very high nutrient concentration in the lake water. Suitable biological （absence of filter-feeding silver carp and bighead carp） and physical environment （high transparency, high stability and high pH） associate with saturated nutrient concentration contribute to the nuisance Mieroeystis bloom in the enclosures.