Application of probability graph for understanding nitrate variation in river water: a case study in northern Anhui Province, China

Water in river is important for human beings. For better understanding the variations of nitrate concentrations in five main rivers in northern Anhui Province, China, the NH₄⁺-N concentrations of the 168 river water samples collected during 2010 have been analyzed by probability graph. The results indicate that the concentrations of NH₄⁺-N vary significantly, which implying the multi contributions of nitrate in the river. In comparison with the water quality standards of China, most of the samples (76.6%) can be used for agricultural and industrial purpose, and more than half of the samples (53.6%) can be used for drinking purpose. Moreover, probability plots, in combination with quantile and density plots have subdivided the concentrations of NH₄⁺-N into five populations with four thresholds (0.28, 0.70, 1.64 and 6.14 mg/l), the concentrations <0.28 and 1.64 mg/l are considered to be representative of pristine and current environmental background, respectively, and concentrations >1.64 mg/l are considered to be representative of anthropogenic pollution.