Spatio-temporal Distribution Of Nutrients In Incipient Three Gorges Reservoir Water In Chongqing

Aquatic eutrophication is a prevalent ecological problem, eutropication can be understood as a phenomenon of the enrichment of nutrients in a water body due to an increase in nutrient loading. The most important nutrients that cause eutropication are Phosphorus and Nitrogen.The most prominent features of eutrophic water is abundance of planktonic or attached algae. According to research of the organization for economic cooperation and development, about eighty percent of aquatic eutrophication are relation to Phosphorus, ten percent are relation to Phosphorus and Nitrogen.The three Gorges reservoir project started water storage in June 2003, hydrology condition of reservoir area were changed greatly. When the water level would finally reach up to 175 meters in 2009,and water flow velocity would decrease from 2 m s~-1 to 0.1 m s~-1, as another consequence, a series of factors resulted from damming, such as lower water flow velocity, higher transparence, would be optimal for photosynthesis of aquatic plant, especially algae, which could potentially lead to eutrophication. However, Studies on eutrophication of the Three Gorges Reservoir are focused on water quality forecast and tributary, Study on nutrients are focused on Changjiang River estuary, few study on the nutrient in the mainstream of Changjiang River have been reported.The study of aquatic eutrophication in the Three Gorges Reservoir area are different from ordinary river and reservoir because of the special hydrology condition of the water body. Therefore, to investigate the distribution characteristics of nutrient of the Three Gorges Reservoir has significant meaning to further study on eutropication . By means of field examination and sampling, nutrient concentration and spatio-temporal distribution of water in the Three Gorges Reservoir before and after impoundment were studied. To investigate different pollution sources to the Three Gorges Reservoir water body, which would provide referenced data to protect the water body.Seasonal distribution of different sampling sites in upriver (Zhutuo), backwater area (Qingxichang) and reservoir area (Wanzhou) are similar, seasonal distribution of nutrients were not affected by hydrology condition. Distribution of Total Nitrogen is similar to Nitrate, Distribution of Total Phosphorus is similar to Particle Phosphorus, concentration of Total Phosphorus and Particle Phosphorus in flood season were higher than which in dry season and normal season.Three forms of Inorganic Nitrogen were detected in Changjiang River, the main existence form of inorganic Nitrogen in Changjiang River was Nitrate with sixty to ninety percent, and the concentration of Ammonia is higher than Nitrite. Nutrients structure of Inorganic Nitrogen varied seasonlly, but the characteristic was not obvious. Nutrients structure of Inorganic Nitrogen in upriver, backwater area were similar to reservoir area. The main existence form of Total Phosphorus was Particle Phosphorus with seventy five to ninety five percent in flood season, while The main existence form of Total Phosphorus was Dissolved Total Phosphorus with thirty to seventy eight percentage in dry season. Concentration of Particle Phosphorus in Zhutuo was higher than which in Qingxichang and Wanzhou in 2004. The ratio of Total Nitrogen to Total Phosphorus ranged from thirteen to twenty four, which showed that Phosphorus was the limit factor of the primary productivity.Concentration of Suspended Substance in flood season was higer than which in dry season before and after impoundment. Concentration of Suspended Substance before impoundment were higher than which after impoundment in reservoir area, and Concentration of Suspended Substance in upriver and backwater area were higher than which in reservoir area due to the slower velocity after impoundment. As a whole, after the water level reached up to 135 meters, no significant difference of Nitrogen and Phosphorus in the horizontal distribution, and so did Nitrogen and Phosphorus in the vertical distribution in upriver (Zhutuo), backwater area (Qingxichang) and reservoir area (Wanzhou).Based on current situation, Provided the discharge method of nutrients in the upriver stays the same, nutrient loads at 175 meters were predicted. Total Nitrogen, Total Phosphorus and Ammonia would be 419627 tons, 106939 tons and 29078 tons per year. Nutrients load from upriver was the highest and the Nutrients load from Jialing River was the second among industrial pollution load, municipal sewage load, pollution load of runoff and pollution load of agriculture. And Nutrients load in flood season were higher than which in dry season. There are significantly positive correlation between Nutrients load and flux.In summary, after the water level reached up to 135 meters, water flow velocity have decreasedfrom backwater area to reservoir area, but there is no significant change of nutrients spatio-temporal distribution were detected except concentration of Suspended Substance and Particle Phosphorus inreservoir area decreased.