[Trophic states and nutrient output of tributaries bay in Three Gorges Reservoir after impoundment].

After the Three Gorges Reservoir storaged water in June 2003, total phosphorus (TP), total nitrogen (TN), chlorophyll a (Chl-a), potassium permanganate index and Secchi depth (SD) were determined in 12 tributaries bay in Three Gorges Reservoir. Trophic states were assessed and output fluxes of TN, TP and potassium permanganate index were calculated. The results showed that value of TN,TP, potassium permanganate index, SD and Chl-a were different in each tributary bay. SD, TN, TP, potassium permanganate index and Chl-a value were 0.10-3.5m, 0.535-7.47 mg x L(-1), 0.016-0.835 mg x L(-1), 1.55-5.88 mg x L(-1) and 1.38-23.7 mg x m(-3) respectively. The water body of tributaries is polluted at various levels. The concentration of TN is abundant. The rate of TN and TP showed that a part of tributaries eutrophication were limited by TP. The correlation of nutrient and Chl-a were researched. It indicated there was a significant positive correlation (r = 0.6242) between chlorophyll a and potassium permanganate index. Utilizing the method of integrated nutrition state index, it assessed the trophic states degree of tributaries bay. The integrated nutrition state index ranged from 33.3 to 66.1. Among all of the studied tributaries, 5 tributaries are eutrophic in May and 8 tributaries are eutrophic in June. The rest of tributaries are mesotrophic. The degree of eutrophication is more serious than before the Three Gorges Reservoir impoundment. The nutrient fluxes load was calculated by discharge and concentration of each tributary. The nutrient fluxes load of TN, TP, potassium permanganate index and NH4(+)-N are 668, 26.7, 890 and 99.2 g x s(-1) respectively. After the Three Gorges Dam was completed in 2009, eutrophication trend of tributaries estuaries will be more serious with the more slow flow velocity.