Greenhouse gas dynamics in fishponds: management versus environmental controls in a complex aqua-agriculture system, France.

Fishponds are hotspots for carbon sequestration, processing, and emissions. However, the environmental drivers of greenhouse gas (GHG) fluxes in these ecosystems remain poorly understood. This study investigates how management practices influence GHG dynamics during the wet phase. We hypothesize that management alters water and sediment characteristics, thereby affecting GHG dynamics. In summer 2023, we measured CO2 and CH4 concentrations, along with water and sediment characteristics, in 38 ponds in La Dombes (France) in response to fertilization, feeding, liming and drying. GHG concentrations varied widely (CO2: 0.99-275.6 μmol L-1, CH4: 0.20-32.45 μmol L-1) and fluxes ranged from -10.1-148.4 mmol m2·d-1 for CO2 and from 0.1 to 20.1 mmol m2·d-1 for CH4. Fish-farming practices primarily influenced sediment-rather than water-properties. CO2 concentrations were negatively related to dissolved oxygen and pH, positively influenced by feeding, which together explained 75 % of variability. CH4 dynamics appeared more complex, likely due to shallow depths, ebullition, and local environmental heterogeneity. This study highlights the strong variability in GHG emissions among ponds, partly mediated by fish-farming practices, and provides insights into their environmental drivers. Further research, including seasonal monitoring and experimental approaches, is needed to identify key management-related factors to help mitigate the climate impact of fish-farming.