Variations and driving factors for concentrations and carbon isotopes of dissolved CO2 in lake water across different Chinese lakes

Abstract

Carbon dioxide (CO₂) stands as the primary driver of Earth's greenhouse effect, and it's suggested that the global contribution of CO₂ emissions from lakes cannot be ignored. Despite the numerous estimations of CO₂ fluxes from lakes, limited focus has been directed towards the carbon isotopes (δ¹³C) of dissolved CO₂ in lake water. Particularly, the potential use of δ¹³C values in tracing the CO₂ concentrations in lake water remains as an understudied area, warranting further exploration and investigation. In this study, we conducted an analysis of the concentrations and δ¹³C values of dissolved CO₂ in 33 lakes located at the Tibetan Plateau, Chinese Loess Plateau, and Yangtze Plain (among which high-resolution spatial investigations were performed in 6 lakes through in-situ continuous monitoring). Our findings revealed spatial variations in both the CO₂ concentrations and δ¹³C values in lakes. Additionally, notable differences are observed among lakes in different regions of China, with lakes in the Yangtze Plain exhibiting considerably higher CO₂ concentrations, and the overall CO₂ δ¹³C values in lakes on the Tibetan Plateau tend to be more positive, while those in lakes on the Chinese Loess Plateau tend to be more negative. The pH values, dissolved oxygen, and dissolved organic carbon are likely crucial factors influencing the CO₂ concentrations and δ¹³C values in the lakes. Furthermore, lake water CO₂ concentrations are negatively correlated with δ¹³C values of CO₂ and dissolved inorganic carbon (DIC) both within a single lake with high spatial resolutions or in lake groups across different regions. These results highlight that the CO₂/DIC δ¹³C values can be applied to trace the concentration variations of dissolved CO₂ in lakes.