Effects of sediment phosphorus release associated with the density current on water quality of a subtropical and deep reservoir in Taiwan

It was found that the increase of sediment P release in the anoxic state associated with the density current initiated by the cold front in the winter was the cause of the deterioration of the water quality of the subtropical, noncalcareous and deep reservoir, Feitsui Reservoir, in recent years. A mathematical model including the analytical solutions of the transport of the density current combined with a simple 2-layered water quality model has been established, describing the hydrodynamics and the water quality variation of the reservoir well. The continued sediment release of P in the anoxic state (from October to March) is an important P source and should be carefully assessed and controlled to reduce the impact of the internal loading of P incorporated with the density current on the water quality in future years.