Abstract: In order to control environmental capacity divisionally in time-sharing way, in this paper the water quality monitoring data measured during the period from 2000 to 2004 were used to analyze the spatiotemporal variation of the 4 main pollution factors and their relationships with runoff volume of mainstream section of the Weihe River in Shaanxi Province. The result are as follows: (1) Permanganate index, ammonium ion and the BOD concentration were in an increase trend at all the cross sections, but the DO was in a decrease trend; (2) The annual variation of permanganate index at all the cross sections was relatively low, but the variation of BOD along the river section close to the urban area was intensive and in an increase trend year by year; (3) There was a significant negative exponent correlation between the permanganate index and ammonium; (4) There was an extreme value of runoff volume for the variation of permanganate index and ammonium ion concentration, when the runoff volume of the river was higher than the extreme value, an enough self-cleaning capability of the river could be maintained; on the contrary, stream water would be further polluted. The study results can be referred for achieving the goal of the coordinated development of economy and environment in the Weihe River Basin.

Key words: water pollution, spatiotemporal variation, runoff volume, environmental capacity, Weihe River