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 diffusive concentrations and 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 (8,790 ± 4,330 tkg CO₂ ha⁻¹ summer⁻¹), CH₄ exerted a far greater climate impact when expressed as sustained global warming potential (32,860 ± 30,710 tkg CO₂ ha⁻¹ summer⁻¹). CH₄ fluxes peaked in warmer months, while CO₂ patterns were more variable, likely linked to photosynthesis and macrophyte biomass. Dissolved CH₄ declined with depth, pH, oxygen, and nitrogen, whereas dissolved CO₂ declined with depth and pH but increased with air pressure, carbon, and sediment depth. These results demonstrate that GHG emissions from agricultural ponds are shaped by interacting physico-chemical and morphological factors, with implications for both carbon cycling and ecosystem services. Integrating pond-scale emissions into broader climate and land-use policies is essential for accurate carbon budgeting.