Expansion and drivers of cyanobacterial blooms in Lake Taihu

The diversity in proxies and drivers of cyanobacterial blooms expansion increased the confusion of understanding for cyanobacterial blooms expansion to scientists and lake managers. This study integrated the previous studies about long-term variation of cyanobacterial blooms in Lake Taihu, and divided the expansion into three aspects: temporal expansion, spatial expansion and biomass expansion, and discussed their trend and drivers. In time, the occurrence of cyanobacterial blooms shows the trend towards spring and autumn/winter from summer. The onset time of cyanobacterial blooms advances, and the annual peak delays. In space, cyanobacterial blooms expands towards center and east of the lake from the north and west. The cyanobacterial biomass increases gradually since 2003. Wind speed and sunshine hours are the primary factors influencing the temporal expansion. Decreasing wind speed and increasing sunshine hours favor the temporal expansion. The drivers for the spatial expansion are relative complicated, and difficult to disentangle the primary factors from nutrient and climate variables. Generally, the occasional large-area cyanobacterial blooms are driven by wind speed and wind direction, and the frequent large-area blooms are driven by nutrient. Total phosphorus is the primary factor driving the variation of cyanobacterial biomass, following by the ratio of total nitrogen to total phosphorus, underwater available light and wind speed. At present, the cyanobacterial blooms area and biomass usually are used to indicate the blooms intensity, both of which are inaccurate due to the defect of methods. Their proxies are reliable for long-term study, but seriously affected by defect of methods when they are used in short-term study. Therefore, it is necessary to build a new proxy as a substitution for bloom area and biomass to show the total cyanobacterial biomass in the whole lake. In addition, reducing phosphorus loading and decreasing phosphorus concentration are the main task of controlling cyanobacterial blooms in Lake Taihu. © 2019 by Journal of Lake Sciences.