COMPARATIVE RESEARCH ON PHYSICOCHEMICAL FACTORS IN THE FRONT OF THREE GORGES RESERVOIR BEFORE AND AFTER THE INITIATE IMPOUNDING

Based on the routine monitoring in the front region of Three Gorges reservoir from 2002 to 2004, the physicochemicalindices were analyzed, and the significant tests for the investigated data before and after the initial impounding were carried out.The results indicated that the major physicochemical indices were not significant differences spatially, but mainly vary with time.Some indices were significantly different before and after impounding.Among them, the annual averages of TN 、TP reduced from2.38mg/L 、0.274mg/L before impounding to 1.62mg/L 、0.132mg/L after impounding respectively.Among inorganic nitrogens,NO3-N was as high as 91.25%,whileNO2-N was only 1.05%, indicating that the Three Gorges Reservoir has great self-purificationcapacity.The results also showed that monthly averages of transparency and turbidity changed greatly, the two indices were negativelyrelated, and transparency decreased and turbidity increased significantly during July to September, which implied that there wereheavy soil erosion during rainfall seasons in this area.Meanwhile, TP also increased significantly along with turbidity increase,indicating that phosphorus pollution is heavy in the soil erosion area.However, since PO4-P deceased at the same time, it alsoindicated that this phosphorus pollution could not be effectively changed to PO4-P.Based on the evaluation of the trophic state indices (TSIM), the front region of the Three-Gorges reservoir was still middleeutrophical due to huge pollution basis (TSIM >37), although the water pollution reduced much after the impounding.At last, we compared the major physicochemical indices with those of other large local reservoirs, the results showed thatconcentrations of TP 、NO3-N in the studying area were much greater.