Quantifying the contribution of methane diffusion and ebullition from agricultural ditches

Abstract

Agricultural ditches are significant methane (CH4) sources since substantial nutrient inputs stimulate CH4 production and emission. However, few studies have quantified the role of diffusion and ebullition pathways in total CH4 emission from agricultural ditches. This study measured the spatiotemporal variations of diffusive and ebullitive CH4 fluxes from a multi-level ditch system in a typical temperate agriculture area, and assessed their contributions to the total CH4 emission. Results illustrated that the mean annual CH4 flux in the ditch system reached 1475.1 mg m−2 d−1, among which 1376.7 mg m−2 d−1 was emitted via diffusion and 98.5 mg m−2 d−1 via ebullition. Both diffusive and ebullitive fluxes varied significantly across different types of ditches and seasons, with diffusion dominating CH4 emission in middle-size ditches and ebullition dominating in large-size ditches. Diffusion was primarily driven by large nutrient inputs from adjacent farmlands, while hydrological factors like water temperature and depth controlled ebullition. Overall, CH4 emission accounted for 86 % of the global warming potential across the ditch system, with 81 % attributed to diffusion and 5 % to ebullition. This study highlights the importance of agricultural ditches as hotspots for CH4 emissions, particularly the dominant role of the diffusion pathway.