Variations in δ 13 C DIC and Influencing Factors in a Shallow Macrophytic Lake on the Qinghai–Tibetan Plateau: Implications for the Regional Carbon Cycle and Sustainable Development

Lake carbon cycle in lake ecosystems is critical for regional carbon management. The application of carbon isotope techniques to terrestrial and aquatic ecosystems can accurately elucidate carbon flow and carbon cycling. Lake ecosystems on the Qinghai–Tibetan Plateau are fragile and sensitive to climate and environment changes, and the carbon cycle impact on the carbon isotopic composition (δ 13 C) of dissolved inorganic carbon (DIC) in these systems has not been well studied, limiting the ability to devise effective management strategies. This study explored the relationship among the δ 13 C position of the DIC (δ 13 C DIC ) in Genggahai Lake, the lake environment, and the climate of the watershed based on the observed physicochemical parameters of water in areas with different types of submerged macrophyte communities, combined with concomitant temperature and precipitation changes. Overall, the Genggahai Basin δ 13 C DIC exhibited a large value range; the average δ 13 C DIC for inflowing spring water was the most negative, followed by the Shazhuyu River, and then lake water. Variations in the photosynthetic intensity of different aquatic plants yielded significantly changing δ 13 C DIC-L values in areas with varied aquatic plant communities. Hydrochemical observations revealed that δ 13 C DIC-I and aquatic plant photosynthesis primarily affected the differences in the δ 13 C DIC-L values of Genggahai Lake, thereby identifying them as the key carbon cycle components in the lake. This improves the understanding of the carbon cycle mechanism of the Qinghai–Tibetan Plateau Lake ecosystem, which is beneficial to improving sustainable lake development strategies.