Spatial and seasonal patterns of size-fractionated phytoplankton growth in Lake Taihu

Abstract

Lake Taihu, a large eutrophic freshwater lake in China, has suffered severe Microcystis blooms since the mid-1980s. In situ nutrient enrichment experiments were conducted to investigate the spatial and seasonal patterns of size-fractionated phytoplankton growth in Lake Taihu. Growth rates were significantly higher in western Taihu than in Meiliang Bay, except in May and September. In western Taihu, phytoplankton growth was only slightly limited by phosphorus. In Meiliang Bay, phytoplankton growth was phosphorus limited during May-July, whereas it was nitrogen limited during August-September. Switching between phosphorus and nitrogen limitation closely followed the seasonal fluctuations in levels of these nutrients. Phytoplankton in the large-size fraction tended to dominate the phytoplankton communities during the Microcystis blooms, although the growth rate of the small-size fraction was significantly higher than that of the large-size fraction. Our results demonstrate that nitrogen and phosphorus levels control the phytoplankton growth patterns in Lake Taihu, and that colonial Microcystis may be critical to maintain blooms under nutrient-limited conditions. © 2014 The Author 2014.