Meteorological and hydrological conditions driving the formation and disappearance of black blooms, an ecological disaster phenomena of eutrophication and algal blooms.

Potentially toxic black blooms can disrupt drinking water treatment plants and have fatal effects on aquatic ecosystems; therefore, lake management is required to determine whether conditions are favorable for the formation and disappearance of black blooms in water supply sources. Long-term climate background, short-term thresholds of meteorological and hydrological conditions, and the duration of harmful algal blooms (HABs) were investigated as factors affecting the formation and disappearance of black blooms in hyper-eutrophic Lake Taihu. Long-term climate warming (0.31°C/decade), decreases in wind speed (0.26m/s per decade) and air pressure (0.16hPa/decade), and the increase in the meteorological index of black blooms (3.6days/decade) in Lake Taihu over the past 51years provided climate conditions conducive to the formation and occurrence of black blooms. A total of 16 black bloom events with an area larger than 0.1km(2) were observed from 2007 to 2014. Several critical thresholds for short-term meteorological and hydrological conditions were determined for the formation of black blooms, including a five-day average air temperature above 25°C, a five-day average wind speed <2.6m/s, average precipitation of five consecutive days close to 0, and continuous HAB accumulation for >5days. Heavy precipitation events, sudden cooling, and large wind disturbances were the driving factors of black blooms' disappearance. The use of a coupling model that combines the remote sensing of HABs with environmental, meteorological, and hydrological observations could permit an adequate and timely response to black blooms in drinking water sources.