Variations in δ 13 C DIC and influencing factors in a shallow macrophytic lake on the Qinghai-Tibetan Plateau: implications for the lake carbon cycle

The primary sources of dissolved inorganic carbon (DIC) in water are carbonate materials and CO 2 produced during the biological processing of organic matter. The application of carbon isotope techniques to terrestrial and aquatic ecosystems can accurately elucidate carbon fluxes and other carbon cycle processes in these systems. Lake ecosystems on the Qinghai-Tibetan Plateau are fragile and sensitive to changes in climate and environment. This study explored the relationship between the carbon isotopic composition (δ 13 C) of the DIC (δ 13 C DIC ) in the 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 changes in the temperature and precipitation during the same period. Overall, the δ 13 C DIC of the Genggahai Basin exhibited a large range of values, with an average δ 13 C DIC for inflowing spring water (δ 13 C DIC-I ) of –11.1 ‰, which was the most negative, followed by an average δ 13 C DIC value of –10.8 ‰ for that from the Shazhuyu River (δ 13 C DIC-R ) and an averageδ 13 C DIC value of –6.91 ‰ for lake water (δ 13 C DIC-L ). Variations in the photosynthetic activity intensity of different aquatic plants yield 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 the Genggahai Lake, thereby identifying them as the key components of the lake carbon cycle.