Numerical Study on Phosphorus Distribution in Water Environment of the Three Gorges Reservoir
|Keywords||sediment adsorption and desorption the biological role nutrients numerical simulation the Three Gorges Reservoir Area|
The effect of water conservancy projects on water ecologic environment in river is now a broad attentive problem. The Three Gorges water quality data in the before (2002.9-2003.6)/ initial (2004.5-2004.9)/ after (2008.1-2008.12) impoundment period show that, since the reservation of water, the water velocity has slowed down and sedimentation appeared seriously, the distribution characteristic of phosphorus in water change as well. Phosphorus concentration on sediment-laden water is larger than in clean water. So the research on retention effect of sedimentation and biological effect is very important for the improvement of the water environment and has significant theoretical and practical value.According to the analysis on the water quality data about reservoir area in the before/initial/after impoundment period, the results are as follows: sediment deposition and sediment adsorption of phosphorus appears obviously in reservoir area since impoundment; Phosphorus concentration on sediment-laden water is larger than clean water, which infers sorption on phosphorus of the sediment. The 2008 reservoir monitoring data show that dissolved phosphorus concentration increases along the river in most months through the whole year.The water quality model which has considered sediment and biology effects on phosphorus concentration is developed and verified, the results show that it can well simulate the movement of water and sediment as well as the phosphorus movement characteristics. In the water quality model, the sediment influence on nutrients is reflected through the coefficient of adsorption and desorption, the reflection of the biological on nutrients is through the adjusted coefficient which reflects the combined effect.Monitoring data is adopted to get the parameters and validate the reliability, numerical simulation analysis are applied to phosphorus concentration of different periods. Four scenario simulations are applied to show distribution characteristic of phosphorus: just solute’s transport and diffusion; just biological effect; just adsorption/desorbs of sediment; adsorption/desorbs of sediment and biological effect. The adsorption and desorption of the sediment on the nutrients and biological effects have significant impact on the nutrient concentrations in water.In this paper, the established numerical model can well reflect water movement, sediment movement with the flow, adsorption and desorption of sediment on the nutrients and biological impact on the nutrients. It can reflect the influence on the sediment and biological effect on the water environment.