Village ponds are hotspots of CO2 and CH4 emissions regulated by biological communities.

Ponds in rural villages (village ponds) potentially emit substantial greenhouse gases (GHG), since they are pervasive and often highly eutrophic. However, few studies report GHG emissions from village ponds, which brings uncertainty in estimating GHG emission budgets. Here, we seasonally measured CO2 and CH4 concentrations and estimated their diffusive emissions from fourteen village ponds, either phytoplankton-dominated (PDPs) or free-floating plant-dominated (FDPs), across the North China Plain. The village ponds exhibited high (mean ± SD) concentrations and diffusive fluxes of CO2 (9.20 ± 0.56 mg-CO2 L-1 and 186 ± 367 mg-CO2 m-2 h-1) and CH4 (1.63 ± 4.21 mg-CH4 L-1 and 33.7 ± 82.1 mg-CH4 m-2 h-1), with FDPs (475 ± 492 mg-CO2 m-2 h-1 and 87.6 ± 120 mg-CH4 m-2 h-1) tremendously exceeding PDPs (20.74 ± 54.60 mg-CO2 m-2 h-1 and 2.92 ± 2.49 mg-CH4 m-2 h-1). Cumulatively, village ponds in the North China Plain were estimated to emit diffusive 10.39 (0.92-26.54) Tg CO2-eq yr-1, equaling 8.54 % of the total CO2 and CH4 emissions from lakes and reservoirs in China, although their area is only 0.88 % of the latter. Therefore, village ponds are hotspots of GHG emissions and should be incorporated in regional and national GHG budgets.