CHARACTERISTICS OF SPRING ALGAL BLOOMS UNDER DIFFERENT IMPOUNDED LEVELS IN TRIBUTARIES OF THE THREE GORGES RESERVOIR

This study analyzed the characteristics of algal blooms based on the spring algal blooms data collected from the tributaries of Three Gorges Reservoir from 2004 to 2015. Results showed that the algal blooms had occurred in 26 tributaries of Three Gorges Reservoir (TGR) with the highest rate in Xiangxi River. The dominant species of the algal blooms were Bacillariophyta and Dinophyta. The probability of Dinoflagellate blooms increased correspondently with the increased impounded level, but the occurrence rate of Diatom blooms increased after several years while reserving water level was up to 175 m. The concentrations of algae density, chlorophyll a and trophic state were low when the reservoir water level was below 175 meters, and then increased sharply when the reservoir water level raised to 175 meters with a trend of gradual decrease after years of reservoir impounding to 175 meters. The principal components analysis (PCA) showed that the algae density, chlorophyll a concentration, total phosphorus (TP), total nitrogen (TN) and permanganate index were classified into the same cluster. Algal density and chlorophyll a concentration were significantly positively correlated with TP, dissolved oxygen, permanganate index and pH. With the impounded level of Three Gorges Reservoir, the mean flow velocity of the tributaries decreased, which might result in the algal blooms at the tributaries of Three Gorges Reservoir under proper temperatures.