Greenhouse gas fluxes in mangrove forest soil in the Amazon estuary

Abstract. Tropical mangrove forests are important carbon sinks, the soil being the main reservoir of this chemical element. Understanding the variability and the key factors that control fluxes is critical to account for greenhouse gas (GHG) emissions, especially in a scenario of global climate change. The current study is the first to quantify methane (CH4) and carbon dioxide (CO2) emissions using a dynamic chamber in Amazon natural mangrove soils. Sampling points were selected in a contrasting topographic gradient, the highest point being where flooding occurs only at high tides during the solstice and on the high tides of the rainy season of the new and full moons. The results showed that mangrove soils are sources of greenhouse gases, and CO2 fluxes were not different between seasons, and only in the dry period were they greater in the high topography. Only in the low topography, the CH4 fluxes were higher in the rainy season. However, in the dry period, the low topography soil produced more CH4. Soil organic matter, carbon and nitrogen ratio (C / N), and redox potential influenced the annual and seasonal variation of CO2 emissions; however, they did not influence CH4 flux. To account for global GHG emissions, in the Amazonian estuary mangrove soil produced 35.4 Mg CO2-eq ha−1 yr−1.