Seasonal variability of tropical wetland CH4 emissions: the role of the methanogen-available carbon pool

[摘要] We develop a dynamic methanogen-available carbon model (DMCM) to quantifythe role of the methanogen-available carbon pool in determining the spatialand temporal variability of tropical wetland CH₄ emissions over seasonaltimescales. We fit DMCM parameters to satellite observations of CH₄ columns from SCIAMACHY CH₄ and equivalent water height (EWH) from GRACE. Over the AmazonRiver basin we found substantial seasonal variability of this carbon pool(coefficient of variation = 28 ± 22%) and a rapid decay constant(φ = 0.017 day⁻¹), in agreement with available laboratory measurements, suggesting that plant litter is likely the prominent methanogen carbon source over this region.Using the DMCM we derived global CH₄ emissions for 2003–2009,and determined the resulting seasonal variability of atmospheric CH₄on a global scale using the GEOS-Chem atmospheric chemistry and transport model.First, we estimated that tropical emissions amounted to 111.1 Tg CH₄ yr⁻¹,of which 24% was emitted from Amazon wetlands. We estimated that annual tropical wetlandemissions increased by 3.4 Tg CH₄ yr⁻¹ between 2003 and 2009.Second, we found that the model was able to reproduce the observed seasonallag of CH₄ concentrations peaking 1–3 months before peak EWH values.We also found that our estimates of CH₄ emissions substantially improved thecomparison between the model and observed CH₄ surface concentrations (r = 0.9).We anticipate that these new insights from the DMCM represent a fundamental step inparameterising tropical wetland CH₄ emissions and quantifying the seasonalvariability and future trends of tropical CH₄ emissions.

[学科分类] 地球化学与岩石