With the industrialization and urbanization of society, nitrogen (N) pollution has become a worldwide environmental problem. Excess nitrogen can result in eutrophication and many other ecological problems, and thus quantifying nitrogen sources in waterways is critical for pollution prevention and control. 

Under the supervision of Professor ZHANG Quanfa, PhD student YUAN Jie from Wuhan Botanical Garden analyzed the N pollution and traced the sources of nitrate and suspended organic Nin the Jinshui River-a tributary of Han River. 

Spatio-temporal inorganic N concentrations differed significantly along the longitudinal gradient in the river network. The ¹⁵N tracing studies demonstrated that N in suspended organic matter was in the form of suspended particulate nitrogen (SPN), mainly deriving from atmospheric deposition and agricultural fertilizer. In contrast, N in stream waters was mainly in the form of nitrate and was from atmospheric deposition, fertilizers, soil, and sewage.  The value of  δ¹⁵N-SPN and δ¹⁵N-NO₃^- peaked in the rainy seasonbecause of more terrestrial inputs of N from sewage or manure via rain runoff.  

This study provides useful information on the nitrate sources of solutes and particles at seasonal and spatial scales using isotope compositions and consequently guides policy makers to improve the ecological quality in the upper Han River. 

It was supported by the National Natural Science Foundation of China. Relevant research results entitled “Characterization and source identification of nitrogen in a riverinesystem of monsoon-climate region, China” was published on the Science of the Total Environment.