The effects of anthropogenic nutrient inputs on stable carbon and nitrogen isotopes in suspended particulate organic matter in Jiaozhou Bay, China

The values of delta C-13 and delta N-15 in POM and nutrient concentrations were investigated in the surface water of Jiaozhou Bay during spring, summer and autumn. Results showed that eutrophic conditions were generally the highest in the northeastern bay during the three seasons. It suggested the sewage from urban rivers were the major pollution source in the northeastern Jiaozhou Bay. The delta C-13 value of POM was significantly higher in the inner bay in spring, but lower in summer. Seasonal distribution of delta C-13 in POM seems depended on the balance between terrigenous organic matter input and in situ phytoplankton biomass. In contrast, delta N-15(POM) showed a consistent distribution pattern during the three seasons, where it was higher in the northwest and lower in the northeast. It suggests that a different source or intensity of anthropogenic nutrient loading may have an opposite effect on the delta N-15 value of POM. The significantly depleted N-1(5) in POM indicated the strong influence of urban sewage in northeastern Jiaozhou Bay. This study suggested the delta C-13 and delta N-15 of POM can effectively indicate the influence of anthropogenic nutrients loading in coastal bays. However, the effects may vary depending on the source and strength of nutrients loading.