Characteristics of stable nitrogen isotopes in particulate organic matter and periphyton of a subtropical Chinese watercourse, the Dashahe River

The stable nitrogen isotope ratios (δ15N) of particulate organic matter (POM) and periphyton were measured at sites along the Dashahe River, a short subtropical watercourse in SE China. δ15N values of both POM and periphyton tended to increase from upstream to downstream, ranging from 1.1 to 7.4 for periphyton and 1.6 to 7.2 for POM. The δ15N values in both POM and periphyton were depleted at upstream sites with lower concentrations of total nitrogen (TN) and total phosphorus (TP) but enriched at downstream sites with relatively high TN and TP. In addition, δ15N values for POM and periphyton showed a significant negative correlation with distance to the most polluted section of the river, implicating human impact in the pattern of increasing δ15N. This study confirms δ15N in POM and periphyton as an excellent indicator of anthropogenic nitrogen pollution in rivers.