Disproportionate Carbon Emissions: Unveiling the Dominance of Ditches in the Aquatic Systems of Qilihai Wetland, a National Conservation Wetland in Tianjin, China

Inland waters are integral to the global carbon cycle, with varied wetland water bodies contributing to greenhouse gases emissions. A comprehensive study of these emissions across different wetland types is essential for elucidating their underlying carbon emission mechanisms. From November 2021 to October 2022, the study employed the headspace equilibrium and floating chamber method to monitor the CO2 and CH4 concentrations, their emissions, and physical and chemical parameters in the Qilihai Wetland’s water bodies (passing rivers, ponds, and ditches) in Tianjin. The results showed that ditches in the wetland were significant emission hotspots for CO2 and CH4, with the emissions rates being 2.33 ± 0.71 mmol m-2 h-1, 15.53 ± 9.77 μmol m-2 h-1, respectively. Notably, CO2 emission rates from ditches were about 4.9 and 4.3 times than those from rivers and ponds, while CH4 emission rates were approximately 2.9 and 2.3 times, respectively. Methane bubbling, indicated by CH4 diffusion coefficient, was identified as a crucial component of emitted CH4, with fraction exceeding 70% in ditches. Additionally, the study underscored that dissolved carbon (DOC, DIC) concentration and nutrient levels were the primary factors influencing carbon emissions in wetland aquatic systems. Despite covering only 19.1% of the Qilihai Wetland's water area, the ditches contribute disproportionately to its carbon emissions, accounting for 52.9% of the annual average carbon dioxide equivalent for the entire wetland area. This study, highlighting the uneven distribution of carbon emissions relative to ditch areas in the Qilihai Wetland, offers valuable insights and recommendations for the future management of wetland carbon sinks and the regulation of water bodies.