Flux and Influencing Factors of CO₂ Emissions from Inland Water Bodies

The inland water bodies are one of the major sources of CO2 emissions in nature, yet current understanding of this aspect remains incomplete. This study systematically reviews and analyzes the measurement methods for pCO2 and F CO2 in common inland water bodies, including rivers, lakes, wetlands, and groundwater, and evaluates their advantages, limitations, and applicable ranges. The study also explores CO2 emission rates and influencing factors for different types of water bodies and provides an assessment of CO2 emission quantities and carbon sink effects in these water bodies. The results indicate that while the diffusion model method is simple to operate, it is highly influenced by environmental conditions, and the static chamber method provides accurate measurements but is difficult to arrange on a large scale. Currently, the annual CO2 emissions from global inland water bodies, measured using these two methods, are estimated to be between 3 242 to 4 721 TgC/a, primarily from emissions of surface water bodies such as rivers, lakes, reservoirs, and wetlands. In contrast, CO2 emissions from groundwater extraction are only estimated to be between 10 to 30 TgC/a. Climate conditions, carbon form (organic/inorganic), physical-chemical-biological processes, groundwater input, and human activities are the primary factors influencing CO2 emissions from surface waters. However, groundwater geochemical characteristics (e.g., pH, HCO3–, and DOC concentrations) and groundwater exploitation primarily affect CO2 emissions from groundwater. Additionally, CO2 emissions from farmland, drainage channels, and spring water increase the complexity of groundwater carbon emissions. The global annual CO2 absorption by inland water bodies is estimated to range from 3 883 to 4 606 TgC/a, mainly including land carbon burial and CO2 sequestration by photosynthesis, rock weathering, wetland carbon sequestration, etc. After accounting for the carbon sink effect of water bodies, the net CO2 emission from global inland water bodies is estimated to be between –1 364 to 838 TgC/a, indicating that the current CO2 expenditure and income of inland water bodies are basically balanced. Future research should focus more on CO2 emissions from wetlands, small inland water bodies and groundwater to improve the accuracy of estimates.