1990S 1997 Oct-2006 Apr -2006 NH4-N 0.1 0.09 0.6 ± 1.3 0.3 ± 0.36 NO3-N   1.04 2 ± 2.7 1.1 ± 0.9 Sources Chen et al., 2000 Liu et al., 2003 Our study

Table 3: Nitrogen variations during the period of 1990s to 2006.