[Trophic states and nutrient output of tributaries in Three Gorges Reservoir area].

TP, TN, chlorophyll a, potassium permanganate index and secchi depth (SD) and phytoplankton were determined in 15 tributaries of 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 Chla were different in each tributary. SD, TN, TP, potassium permanganate index and Chla value are 0.45 - 1.5 m, 0.65 - 4.27 mg x L(-1), 0.011 - 0.432 mg x L(-1), 0.657 - 5.37 mg x L(-1) and 0.57 - 12.2 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 are limited by TP. Utilizing the method of integrated nutrition state index, it assessed the trophic states degree of tributaries. All of the studied tributaries, 3 tributaries are eutropher, 10 tributaries are mesotropher and 2 tributaries are oligotropher respectively. 129 species of phytoplankton are identified, which belongs to 7 division and 67 genera. The dominant species are Bacillariophyceae, Chiorophyceae and Cyanophyta. The type of phytoplankton community is Bacillariophyceae-Chlorophyceaetype, Bacillariophyceae-Cyanophytatype and Cyanophyta-Chlorophyceaetype. The species and numbers of phytoplankton are various in different tributaries. The nutritive peculiarity belongs to responding type of phytoplankton. The nutrient fluxes load was calculated by discharge and concentration of each tributary. The nutrient fluxes load of TN, TP and potassium permanganate index are 3.14 x 10(5) t, 1.76 x 10(4) t and 2.74 x 10(5) t respectively in one year. After the Three Gorges Dam was completed in 2009, eutrophication trend of tributaries estuaries would be more serious with the decreasing of flow velocity.