Abstract: Threshold analysis of water body eutrophication can provide scientific basis for controlling water bloom and defining pollutants rational control level. Taking the Baiyangdian wetlands as the case, and by using 2000-2009 water quality monitoring data, the main indices characterizing the water body eutrophication of the wetlands were clustered by principal component analysis, and, using chlorophyll a as dependent variable, and water pH, temperature, transparency, COD_cr, total nitrogen, total phosphorus, ammonia nitrogen, nitrate nitrogen, and dissolved inorganic phosphorus as independent variables, the multiple linear relationship of chlorophyll a and water quality indices was established by stepwise regression to determine the thresholds of water blooms in the wetlands. The Baiyangdian wetlands could be categorized into two kind water areas, i.e., low dissolved oxygen and high nutritional, and unstable. With 30 μg·L^-1 of chlorophyll a as the threshold of water bloom, the COD_cr concentration in the low dissolved oxygen and high nutritional water area should be controlled at 37.31 mg·L^-1, and the total phosphorous concentration in the unstable water area should be at 0.12 mg·L^-1.

Key words: Mycorrhiza, Rhizosphere, Heavy metal, Speciation, Bioavailability