Intensifying methane emissions in Chinese Ponds: The interplay of warming, eutrophication, and depth changes

Ponds are significant contributors to global methane (CH₄) emissions. However, accurately estimating their historical or future CH₄ emissions remains challenging, particularly under dynamic environmental changes such as eutrophication, sedimentation-driven shallowing, and global warming. We synthesized 674 observations of CH₄ emission rates to identify key drivers and develop a process-based predictive model. We present a framework for spatially explicit estimation of pond CH₄ emissions in China from 1960 to 2020, accounting for factors such as temperature dependence, depth, nutrient levels, and pond area. Our findings show that pond CH₄ emissions are strongly temperature-dependent, characterized by a high average activation energy (0.834 eV). Notably, ebullitive emissions exhibit greater temperature sensitivity than diffusive emissions. Nitrogen concentrations and water column depth emerged as critical predictors of total CH₄ fluxes. Over the past six decades, CH₄ emissions from Chinese ponds increased approximately 9-fold, from 0.16 Tg CH₄ yr^-1 in 1960 to 1.53 Tg CH₄ yr⁻¹ by 2020, emphasizing their growing role in global methane emissions. Notably, half of these emissions occur during summer, with ebullition accounting for 66 % of the total CH₄ flux. This increase was primarily driven by the interactions of warming, nutrient enrichment, declining water depth, and pond expansion. Our results underscore the growing role of ponds in CH₄ emissions and highlight the urgent need for mitigation measures, such as reducing nutrient loading and implementing periodic dredging management. This study provides a robust foundation for improving CH₄ emission estimates and developing sustainable management practices for ponds in the context of global environmental change.