Earlier and warmer springs increase cyanobacterial (Microcystis spp.) blooms in Lake Taihu.pdf

Earlier and warmer springs increase cyanobacterial (Microcystis spp.) blooms in subtropical Lake Taihu, China J IANMING DENG* ,? , BOQIANG QIN*, HANS W. PAERL?, YUNLIN ZHANG*, J IANRONG MA*,? AND YUWEI CHEN* *State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China ?University of Chinese Academy of Sciences, Beijing, China ?Institute of Marine Sciences, The University of North Carolina at Chapel Hill, Morehead City, NC, U.S.A. SUMMARY 1. We examined the effects of regional warming and water quality on phytoplankton community suc- cession, 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 sea- son has advanced by approximately 20 days over the last two decades, and accumulated air temper- ature (from 1 March to 31 May) has increased significantly. 2. 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. 3. 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 tem- perature promotes their earlier onset and proliferation, a phenomenon previously documented for temperate regions, and now demonstrated for this subtropical lake. Keywords: accumulated temperature, canonical correspondence analysis, climate change, cyanobacterial blooms, Meiliang Bay Introduction Eutrophication, a typical symptom of which is harmful cyanobacterial blooms, i