Methane and carbon dioxide emissions from agricultural ponds are driven by physico-chemical and morphological characteristics

Abstract

Agricultural ponds are globally widespread and multifunctional, yet they emit substantial quantities of greenhouse gases (GHGs), notably methane (CH4) and carbon dioxide (CO2), posing a significant but poorly quantified climate disservice. This study quantified dissolved concentrations and total fluxes of CH4 and CO2 from 18 agricultural ponds in Scotland between May and September. All ponds were net GHG sources, with mean fluxes of 0.39 ± 0.41 g CH4 m-2 day-1 and 3.22 ± 1.91 g CO2 m-2 day-1. While CO2 flux dominated in absolute terms (11.4 ± 5.9 t/ha/year) CH4 had a far greater climate impact when expressed as sustained global warming potential (36.5 ± 35.5 t CO2-eq/ha/year). CH4 fluxes peaked in warmer months, while CO2 patterns were more variable. Dissolved CH4 decreased with depth, pH, oxygen, and nitrogen, while dissolved CO2 decreased with depth and pH but increased with air pressure, carbon, and sediment depth. As human-made ponds are classed as anthropogenic systems, their emissions should be included in national GHG inventories and land-based mitigation strategies. These findings highlight the importance of integrating agricultural pond emissions into climate policy and carbon budgeting.