at the Sanmenxia, the pollution trends of COD_(Mn), NO_2-N, As and Hg are not obvious, the pollution of NH_3-N has an obvious ascend trend, the pollutions of Cd has an obvious drop trend, but the pollutions of Cu and Pb have very marked drop trends.

• 三门峡断面,CODMn、NO2-N、As及Hg的变化趋势不明显,NH3-N污染呈显著上升趋势,Cd呈显著下降趋势,而Cu和Pb则呈高度显著下降趋势。