Abstract: Water eutrophication is a global problem, and one of the major environmental problems in China. At present, its studies in China are mainly focused on lakes and reservoirs, whereas a few on rivers. Based on the stress-response of benthic macroinvertebrate assemblages to water nutrients, we used the nonparametric deviance reduction (change point analysis) to compute the breakpoints of nutrients concentrations,  in the upper reac hes of Xitiao Stream in Zhejiang. The results indicated that the breakpoints of total nitrogen (TN) and total phosphors (TP) were 1.409 mg·L^-1 and 0.033-0.035 mg·L^-1, respectively. The TN and TP concentrations at reference sites were lower, while those at urban sewage- polluted sites were higher than the thresholds. In latter case, a serious degradation of benthic macroinvertebrates assemblages could be induced. To establish water nutrients criteria with relation to aquatic organisms would make the biological monitoring play a full role in water management, and provide scientific data to estimate the total maximum daily load (TMDL) of TN and TP in water body.

Key words: eutrophication, nutrient, threshold, benthic macroinvertebrate, Xitiao Stream, grape, drip irrigation, rootshoot, regulation.