Effect of nitrogen and phosphorus on the water quality in the Three Gorges Reservoir Area during and after its construction.

A survey concerning the concentration of the nutrients in the Three Gorges Reservoir Area was carried out. This paper presents the parameters(NO3- -N, NO2- -N, Kjeldahl-N, non-ionic ammonia, P-PO4 and TP) determined at 16 sampling sites from 1997 to 1999. The dominant soluble nitrogen form was NO3- -N followed by Kjeldahl-N, NO1- -N and non-ionic ammonia. Mean values of NO3- -N, NO2- -N, Kjeldahl-N and non-ionic ammonia ranged from 0.50 to 2.37 mg/L, 0.022 to 0.084 mg/L, 0.33 to 0.99 mg/L and 0.007 to 0.092 mg/L respectively. Mean values of P-PO4 at most sampling sites were higher than 0.1 mg/L for subject to eutrophication. The major factors influencing the concentrations of N and P might be agricultural runoff, municipal and industrial effluents. In addition, 6 kinds of soil were sampled at the area where would inundated after the dam completed. Two approaches were adopted to simulate the N and P release from the inundated soils. The results showed that the soils would release nitrogen and phosphorus to the overlying water when the soils were inundated. The characteristics of soil affected the equilibrium concentrations of N and P between the soil and the overlying water.