Chinese ponds exhibit larger carbon sequestration but smaller carbon emissions than lakes and reservoirs

Abstract China's ponds, which have proliferated in number due to agricultural expansion and population growth, serve as both carbon sinks and sources due to large nutrient influxes. Despite their significance, the role of ponds in the carbon cycle has remained largely unknown, owing to their small size, vast number and widespread distribution. This study integrates carbon emissions and burial across 14.6 million Chinese ponds, revealing their substantial carbon sequestration potential. Ponds emit 5.29 Tg CO2-C yr-1 and 0.86 Tg CH4-C yr-1 but sequester 6.49 Tg C yr-1 of which 82% is organic carbon (OC). In contrast, lakes and reservoirs sequester fluxes of 1.77 Tg C yr-1 and 4.64 Tg C yr-1 of OC, respectively. Considering the high OC-burial/C-emissions ratio (0.86), China’s ponds are more effective as C sinks than lakes and reservoirs. Our results offer a more comprehensive estimate of the C budgets of China's ponds and enhance understanding of their contribution to the global C cycle.