Magnitude e espacialidade do fluxo de metano (CH4) em pisciculturas no estado de Minas Gerais

Abstract

Aquaculture has become an important alternative for increasing the supply of animal protein and strengthening food security, in alignment with the United Nations Sustainable Development Goals (SDGs). In Brazil, fish farming in earthen ponds stands out for its accessibility and potentially lower environmental impact. However, the rapid expansion of the sector makes it essential to quantify its greenhouse gas (GHG) fluxes, particularly in Minas Gerais (MG), the thirdlargest fish-producing state in Brazil. In this study, we quantified the spatial variation in diffusive and ebullitive CH4 fluxes across 227 earthen ponds distributed among 54 fish farms in MG, assessing their relationships with water quality, regional climatic gradients, and cultured species. The median total flux was 61.16 mg CH4 m-2 d -1 , with more than half of the ponds exceeding the IPCC reference value for the “other flooded lands” category (~50 mg CH4 m-2 d -1 ), while the ebullitive pathway accounted for 50.64% of the total, representing a lower predominance than that reported in the literature. When extrapolated to the 4,276 ha of aquaculture water surface area mapped across the state, the flux corresponded to 1.88 Gg CH4 year -1 , or 51.01 Gg CO2-eq year -1 (95% CI: 42.41– 59.92), equivalent to 0.03% of the state’s total GHG emissions. This magnitude, however, was not homogeneously distributed: fluxes were associated with eutrophication, production management, and characteristics of the cultivation systems, while species endemic to MG exhibited the lowest emissions (41.51 mg CH4 m-2 d -1 ), below the IPCC reference value. Dissolved CH4 showed significant spatial dependence at the scales evaluated, indicating that its distribution is also influenced by regional-scale drivers. Consistently, the projected scenarios for 2030 separated ponds by more than three orders of magnitude in fluxes (0.91 to 1,363.62 mg CH4 m-2 d -1 ), indicating that management practices may have a greater influence on future emissions than sectoral growth itself. These results fill important information gaps in a major fish-producing region and provide support for national GHG inventories and the development of mitigation strategies.