Linking Freshwater Wetland Productivity and Methane Emissions: A Global Perspective

Understanding the link between wetland gross primary productivity (GPP) and methane (CH₄) emissions is crucial for global carbon cycle modeling, yet this coupling remains poorly constrained at a global scale due to data limitations. To address this critical gap, we compiled and analyzed the most comprehensive daily scale eddy covariance data set of GPP and CH₄ fluxes. In this analysis, we define this coupling as the slope of the linear fit between carbon fixed by ecosystems and carbon emitted as CH₄. Results indicate that the median lag time between CH₄ emissions and GPP is 24.8 days. In terms of their coupling, for every gram of carbon fixed in wetlands, 0.03 (interquartile range: 0.02-0.05) grams of carbon are released into the atmosphere as CH₄. The upscaling results indicate that the coupling in tropical wetlands is typically larger than in temperate and boreal wetlands, and the CO₂-equivalent emissions of CH₄ surpass the amount of CO₂ absorbed through photosynthesis. These results enhance our understanding of the complex biogeochemical processes that drive CH₄ emissions, offering valuable insights into the interplay between carbon fixation and emissions dynamics in wetland ecosystems.