The effects of temperature and nutrient ratios on Microcystis blooms in Lake Taihu, China: An 11-year investigation

The temporal distribution of bloom-forming cyanobacteria- Microcystis and its correlation with related physical and chemical variables including the total nitrogen-to-total phosphorus ratio (TN:TP), the ammonium-to-nitrate ratio (NH4-N:NOx-N), water temperature, and pH in the north part of Lake Taihu (Meiliang Bay) were investigated, using a continuous, 11-year record of environmental data (1992-2002) and phytoplankton species. A multivariate statistical analysis, canonical correspondence analysis (CCA), revealed a negative correlation between the Microcystis and TN:TP, and a positive correlation between the Microcystis and NH4-N:NOx-N, water temperature and pH. Warm water temperature was the principal force driving Microcystis blooms, which were preceded declining concentrations of nitrogen compounds. Microcystis tended to dominate (Microcystis contributed above 50% to total algal mass) in the north part of Lake Taihu during summer when the TN:TP mass ratio was less than 30. NH4-N:NOx-N was below 1, and a critical water temperature ranged from 25 degrees C to 30 degrees C. respectively. Meanwhile, suspended solids (SS) concentrations exceeded 10 mg l(-1) and pH exceeded 8.0 during blooms. Overall, this study advances our understanding of nutrient enrichment and high ambient temperature influences on Microcystis biomass. (C) 2010 Elsevier B.V. All rights reserved.