Abstract: Eutrophication and nitrate contamination of groundwater in the Taihu Lake region has aroused nationwide concern recently.NO₃ ^- -N and NH 4 +-N concentrations in lake,river and well waters in the Taihu Lake region were monitored twice a month with three replicates in the year from Sept.26,2000 to Sept.26,2001.At the same time,both surface and bottom water sampled from the lakes,rivers and wells four times in the year were analyzed for NO₃ ^- -N and NH₄⁺ -N concentrations.Results demonstrated that the average concentrations of inorganic N (sum of NO₃ ^- -N and NH₄⁺ -N) amounted to 1.14,7.16 and 15.84 mg·L ^-1 in the lake,river and well waters,respectively, all exceeding the limit of eutrophication and the well water had seriously been contaminated by nitrate.Moreover,the major pollutant in the river water was NH₄⁺ -N and in the well water NO₃ ^- -N.The results also indicated that in the lake,river and well waters,there was no obvious difference in NO₃ ^- -N and NH₄⁺ -N concentrations between surface and bottom waters while there was between sampling dates.It is hence concluded that the aquatic systems had been seriously polluted by anthropogenic N.

Key words: Taihu Lake region, non point source pollution, water quality, pollutant