Abstract: Water quality of rainfall changes greatly after passing throngh trees canopy in the watershed.In this paper,an artificial mixed forest was chosen to measure the precipitation inside and outside of the forest, and stemflow as well as the variations of their nutrient contents.By analysing the characteristics of rainfall partitioning ,the water qualilty,the nutrient input and cycling processes were discussed.The results showed that the concentrations of NH₄-N,NO₃-N,P,K,Ca and Mg were different among rainfall,throughfall and stemflow.In accordance with the rainfall partitioning,nutrients entered the field both as point source and area source,from which two different processes of translocation were found.The nutrient contributions in the field by rainfall and leaching from trees were also discussed.

Key words: weight of evidence (WOE) approach, integrated assessment, sediment quality assessment, sediment.