Δ¹³C, Δ¹⁵N and C_org/N_total as tracer for sources of carbon and nitrogen to Yangtze River intertidal zone

The Yangtze River is one of the largest rivers in the world. Because of its social and economic values, the environmental status of the Yangtze River estuary has been of major public concern. Previous studies showed that environmental quality in the Yangtze River estuary is being degraded due to pollution and red tides. Urbanization and economic development in Shanghai have a direct impact on the Yangtze River estuary. Many areas in or adjacent to the intertidal zone are used for commercial harbors, iron and steel mills, and other industrial operations. Runoff and other discharges within the Yangtze River catchment provide additional sources of contamination to the Yangtze River estuary. In order to investigate the source of carbon (C) and nitrogen (N) to the Yangtze River intertidal zone, surface sediment samples (0-5 cm in depth) were collected from 59 stations distributed in 26 different locations within the Yangtze River intertidal zone during 2004 and 2005, and analyzed for C, N, Δ¹³C and Δ¹⁵N. In this study, we found that total organic carbon ranged from 0.08%-1.62%, total nitrogen from 0.02%-0.13%, Δ¹³C from-26.83‰--19.14‰, and Δ¹⁵N from 1.14‰-6.05‰. The study shows that characteristics of carbon and nitrogen distributions in Yangtze River estuary are mainly the consequence of the mixing of natural terrestrial, marine and saltmarsh sources due to hydrodynamic and sediment dynamic processes.