Carbon and nitrogen isotopes analysis and sources of organic matter in the upper reaches of the Chaobai River near Beijing, China

The carbon and nitrogen isotopes in the surface sediments, plants, and soil in the upper reaches of the Chaobai River have been researched. The results showed −27.75‰ — −21.58‰ and 1.32‰-6.74‰ for carbon and nitrogen isotopic ratios in the surface sediments, respectively. The sources of sedimentary organic matter in this area are soil organic matter, aquatic vascular plants, and riverine plankton, respectively, and a significant contributor to sediment in the Chaohe River, the Baihe River, and the Miyun Reservoir areas is soil organic matter. Furthermore, part of sedimentary organic matter in the Miyun Reservoir is attributed to the input from the Chaohe River and the Baihe River, the other is from C4 vegetation growing around individual point stations at the Miyun Reservoir. Compared with the situation in Hebei Province, the contribution of soil organic matter decreased significantly and river plankton and aquatic vascular plants increased significantly in Beijing municipal areas. This study reveals that the source of organic matter has a close relationship with the soil erosion.