From Linear Assumptions to Complex Reality: Dissolved NO3- and N2O Flux Dynamics in Aquacultural Ponds

Nitrous oxide (N₂O) is an ozone-depleting substance with a global warming potential of 273 times greater than carbon dioxide (CO₂) for a 100-year timescale. The atmospheric concentration of N₂O has increased significantly, rising from approximately 270 ppb during the preindustrial era to over 330 ppb today. This alarming trend underscores global concerns about accurately quantifying anthropogenic N₂O sources and developing effective mitigation strategies. More than 50% of anthropogenic N₂O emissions is estimated to originate from direct agricultural activities, including land-use changes, fertilization, and manure management. In addition, agriculture may also indirectly contribute to N₂O emissions through its impact on freshwater eutrophication, which provides substrates (such as nitrate – NO₃⁻) for nitrification and denitrification processes in aquatic environments, potentially leading to N₂O production. The Intergovernmental Panel on Climate Change (IPCC) has proposed a linear correlation between NO₃⁻ concentrations and N₂O emissions to estimate global freshwater contributions to N₂O budgets. In this context, freshwater ecosystems, such as small agricultural ponds, are often considered as net sources of N₂O. However, direct measurements of N₂O dissolved concentrations and N₂O fluxes from agricultural ponds are limited. Actually, some studies have found N₂Odissolved concentration under saturation levels, leading to assume N₂O uptake from agricultural ponds. To better understand the role of agricultural ponds as sinks or sources of N₂O, we conducted a systematic literature review. Based on data from over 200 ponds associated with agricultural production we found that: there is a strong geographical bias, with most studies focusing on ponds in the northern hemisphere, and that there is non-linear relationship between dissolved NO₃⁻ concentrations and N₂O fluxes. These preliminary findings suggest that a re-evaluation of the IPCC's guidelines on N₂O emissions from inland waters is needed as local conditions strongly drive the fate of NO₃^- underscoring the need for further research into the driving factors behind water-atmosphere N₂O fluxes in agricultural ponds.