Daobin Ji

Diel migration of Microcystis during an algal bloom event in the Three Gorges Reservoir, China

The vertical migration patterns and buoyancy regulation of Microcystis in water bodies have important effects on algal bloom formation. To understand the migration mechanism of Microcystis in deep bodies of water, two sets of experiments were carried out to illuminate the complex vertical movements in the Three Gorges Reservoir. Samples were taken during a 46-h period, with detailed monitoring of key parameters such as the solar irradiance, chlorophyll-a concentration, and water temperature. The index of dispersion and mean residence depth were computed to better understand the vertical distribution over time. The Microcystis colonies moved upward from the early morning until noon and sank from the surface in the afternoon and night. The vertical migration of Microcystis was the dominant factor affecting the dynamic changes of Microcystis in the enclosure. The water motion was also important in the diel dynamic changes of the Microcystis distribution. These results enable us to better understand the process of the initiation, development and appearance of blooms and allow us to devise new control strategies of algal bloom.

Stable isotopes in water indicate sources of nutrients that drive algal blooms in the tributary bay of a subtropical reservoir

Eutrophication has become a severe environmental problem in some tributaries of the Three Gorges Reservoir (TGR) in China. A two-year field investigation of nutrients, oxygen stable isotopes (δ18O), and hydrogen stable isotopes (δD) was performed from January 2010 to December 2011 to determine the sources of nutrients in Xiangxi Bay (XXB). The results showed that nitrogen, phosphorus and silicon varied seasonally depending on hydrodynamic changes. The bottom-layer intrusive density current decreased nitrogen and silicon concentrations and increase phosphorus concentrations in XXB, while the middle-layer intrusive density current increased nitrogen and silicon concentrations and decrease phosphorus concentrations. The differences in δ18O and δD among the Yangtze River (YR), XXB and the region upstream of XXB were significant, and according to the tracer method, the estimated contribution ratios of nitrogen, phosphorus and silicon from the YR to XXB were much larger than those from the region upstream of XXB. These findings suggest that water quality in the TGR can be improved by reducing the pollution load throughout the upstream basin of the YR but not through decentralized efforts in only one or two tributary basins.