Mechanisms affecting greenhouse gas emissions from sediments of urban landscape water bodies under different aeration conditions

To explore the impact of aeration conditions on greenhouse gas emissions from urban water bodies, this study conducted indoor incubation experiments using the surface sediments from the lakeside zone of Nanjing Binjiang Wetland Park. Four treatment groups including surface aeration, middle-layer aeration, bottom-layer aeration, and a static control group were set up, with aeration heads placed at different depths (1 cm below the water-air interface for surface aeration, 10 cm for middle-layer aeration, and at the water-sediment interface for bottom-layer aeration). During the 45 d experiment, aeration with air was carried out from 12:00 to 15:00 every day. Samples of gas, water, and sediment were collected at 9:00 daily to measure greenhouse gas emission rates, cumulative emissions, and relevant physical and chemical properties. The results showed that in terms of CO₂ emissions, the middle-layer aeration treatment had the most significant inhibitory effect, with the cumulative CO₂ emissions of the surface, middle-layer, and bottom-layer aeration groups being 67.7%, 60.9%, and 76.7% of the control group respectively; for CH₄ emissions, the surface-water aeration treatment led to the highest cumulative emissions, with the cumulative CH₄ emissions of the surface, middle-layer aeration and bottom-layer aeration groups being 197.3%, 106.7%, and 97.7% of the control group respectively; regarding N₂O emissions, middle- layer water aeration significantly increased emissions, with the cumulative N₂O emissions of the surface, middle- layer, and bottom-layer aeration groups being 112.2%, 146.4%, and 81.9% of the control group respectively, while bottom-layer aeration effectively inhibited N₂O emissions. Additionally, different aeration depths significantly affected the physical and chemical properties of the overlying water and the carbon-nitrogen cycling process. The DO concentration decreased with increasing aeration depth, with the bottom-layer aeration group having a significantly lower DO concentration at the end of the experiment compared to the control group. The pH value showed a single-peak trend of first increasing and then decreasing, with the surface-aeration group having the highest pH initially but the control group having a higher pH than the bottom-layer aeration group at the end of the experiment. The DOC and TC concentrations were highest in the control group and lowest in the middle-layer aeration group. In nitrogen transformation, the bottom-layer aeration group had the lowest NH^₄+-N concentration, the middle-layer aeration significantly increased the NO^₃−-N concentration, the TN concentration was lowest in the bottom-layer aeration group with the highest carbon-nitrogen ratio, and the DOM fluorescence analysis showed that the DOM in each treatment group was mainly terrigenous humus with no significant difference in humification degree. This study clarifies the impact of aeration treatment technology on urban landscape water body greenhouse gas emissions, provides an important theoretical basis for urban landscape water body management and carbon emission accounting, helps understand the complex relationships among aeration, water body environment, and greenhouse gas emissions, and is of great significance for formulating scientific urban water body management strategies and reducing urban greenhouse gas emissions. Moreover, the results can serve as a reference for similar studies in other regions, contributing to global climate change mitigation and sustainable urban water resource management.