Earlier and warmer springs increase cyanobacterial (Microcystis spp.) blooms in subtropical Lake Taihu, China

We examined the effects of regional warming and water quality on phytoplankton community succession, focussing on the bloom-forming cyanobacterial genus Microcystis in subtropical Lake Taihu, China. Daily air temperatures from 1991 to 2010 indicated that onset of the Microcystis growing season has advanced by approximately 20days over the last two decades, and accumulated air temperature (from 1 March to 31 May) has increased significantly. Since 2005, Microcystis blooms have begun in May more frequently than in June. An increase in degree days for growth indicated that the early warming trend in spring would have benefitted Microcystis populations that overwintered on the sediment surface, by allowing them to grow, gain buoyancy and float into water column earlier in the year. Results of canonical correspondence analysis showed that both water quality (i.e. nutrient loading) and water temperature have affected phytoplankton community succession in spring over the past two decades. When nutrient concentrations are adequate to support Microcystis blooms, rising temperature promotes their earlier onset and proliferation, a phenomenon previously documented for temperate regions, and now demonstrated for this subtropical lake.