The Role of Management on Methane Emissions From Subtropical Wetlands Embedded in Agricultural Ecosystems

Wetlands are an important source of CH₄ globally. However, uncertainty surrounding the impact of anthropogenic activities on CH₄ emissions from wetlands limits understanding of how these ecosystems will respond to management changes. Furthermore, by neglecting the potential for management to influence CH₄ emissions likely inflates error of CH₄ emissions for regional and global CH₄ models. This study employed a replicated factorial experimental design to investigate how management of the agricultural landscape, including grazing and/or management intensity, influences net CH₄ emissions from embedded, seasonal subtropical wetlands. This research further determined key mechanisms by which management decisions at the landscape scale modulate CH₄ emissions from the embedded wetlands. Net CH₄ exchange was measured using a closed chamber system over two complete wet/dry seasonal cycles in 16 wetlands embedded in either agronomically improved pastures (improved wetlands) or less intensively grazed unfertilized seminative pastures (seminative wetlands), as well as in grazed and ungrazed wetlands in each treatment. Emissions of CH₄ were higher from improved wetlands (2.82 μmol m⁻² s⁻¹) than seminative wetlands (0.75 μmol m⁻² s⁻¹), particularly during the wet season. Enhanced CH₄ emissions in improved wetlands relative to seminative wetlands were caused by increased soil wetness and by higher biomass in improved seminative wetlands. Unlike subtropical flooded pastures, our results showed that grazers do not alter CH₄ emissions from subtropical wetlands. Current and future changes in management intensity of pastures may cause shifts in net soil CH₄ emissions from embedded subtropical wetlands, which could further enhance this emission source.