Effect of the Three-Gorge Project impoundment on the COD_(Mn),NH_3-N and TP fall coefficients

The paper attempts to bring forward our study results of the effects of the Three-Gorge Project impoundment on the CODMn,NH3-N and TP fall coefficients. As is known,since the impoundment of the Three-Gorge reservoir,serious effects have been brought about on the hydrological conditions in the backwater areas,with the Pengxi river being one of the typical example. In hoping to control the water pollution and water eutrophication in the reservoir area,we think it necessary to study the changes of the pollutant fall coefficients. Thus,in proceeding with our research, we have studied the permanganate index(CODMn),ammonia nitrogen(NH3-N) and the total phosphorus(TP) of the water quality during 2004-2010 with the backwater effects of the reservoir on the Pengxi river as a typical region.The results of our investigation and statistics have shown that the ranges of CODMn,NH3-N and TP concentrations turn to be 1. 4-4. 0 mg / L,0. 03-0. 57 mg / L and 0. 05-0. 16 mg / L respectively.In addition,the high organic pollutant concentrations are likely to take place mainly in the high-tide water period. Based on the water quality monitoring data,we have observed the changes of CODMn,NH3-N,TP fall coefficients before and after the reservoir impoundment in the Pengxi backwater area by using the MIKE21 HD and the ECOLab WQ simulation models. By choosing the statistical area within the distance of 53. 5 km of the Pengxi river in the range between the estuaries to Qukou section in Yunyang city and the main Yangtze reach of 6. 8 km in Shuangjiang city. We have also used the unstructured mesh with13 313 nodes and 20 782 statistical units in the 2D simulation models. The investigation results show that the ranges of CODMn,NH3-N and TP fall coefficients which are worked out at about0. 130-0. 250 d-1,0. 110-0. 180 d-1and 0. 080-0. 130 d-1respectively before the impoundment, and 0. 007-0. 016 d-1,0. 006-0. 015 d-1and 0. 005-0. 012 d-1respectively after the impoundment,with the pollutants fall coefficients after the impoundment being only 1 /20-1 /10 of the coefficients before the impoundment. The reduction of the pollutant fall coefficient stands for the one of the important factors of water pollution in the Pengxi backwater area after the Three-Gorge reservoir impoundment. From what is said above,it can be seen that our proposal should lie in that the pollution under study should be controlled by regulating the pollutant-fall coefficients.