Spatial distribution and environmental significance of modern organic carbon and nitrogen stable isotopes in the source area of the Yellow River: A case study of Gyaring Lake and Ngoring Lake

Organic carbon and total nitrogen isotopes (δ13Corg and δ15N) are useful for identifying sources of organic matter and for reconstructing environmental conditions in paleoecology and paleoclimatology. Gyaring Lake and Ngoring Lake are the two largest freshwater lakes in the source area of the Yellow River (SAYR), which lies in the northeastern the Qinghai–Tibet Plateau. These bodies of water were chosen as our research objects, and we analyzed the carbon and nitrogen isotopes in the surface sediments of the two lakes and in soil samples from around the lakes. The results indicate the consistency and endogenous characteristics of the organic matter sources of the distribution of δ13Corg and δ15N in the surface sediments of Gyaring Lake and Ngoring Lake. The δ13Corg values of the two lakes were significantly positive in areas near the inflow and outflow of the Yellow River. The distribution of δ15N in Gyaring Lake was similar to that of total organic carbon (TOC) and total nitrogen (TN), and its values were relatively higher than those affected by the joint influence of the Yellow River and some small tributaries, while δ15N was more positive in the deep-water area of Ngoring Lake. This study provides reliable and modern data on δ13Corg and δ15N for the long-term paleoenvironment and paleoecological reconstruction of the SAYR in the future.