Understanding Methane Production across Diverse Tropical Peatlands

Abstract:

Natural wetlands are one of the largest sources of CH₄ to the atmosphere. Across the tropics, peatlands are important, yet poorly studied, wetland ecosystems. Although CH₄ production and emissions from tropical peatlands are potentially highly variable globally, prior work has largely focused on ombrotrophic peatlands in Southeast Asia with relatively low CH₄ emissions. In this work, we aim to better understand CH₄ production in more diverse tropical peatlands, using isotopic measurements (δ¹³C and Δ¹⁴C). We assess the C source and methanogenic pathway for methane production across a wide range of peatland ecosystems, selecting sites with divergent vegetation, hydrology and CH₄ emissions rates across the Pastaza-Marañon Basin. The study sites range from ombrotrophic, low pH sites (pH 3-4) to intermediate sites to minerotrophic, less acidic sites (pH 5-6). We observe different methanogenic pathways across the sites, and systematic variation in the δ¹³C of CH₄, from -80 to -110‰ in ombrotrophic sites, to -60 to -75‰ in minerotrophic sites. The Δ¹⁴C of CH₄ reflects recent plant inputs across sites, with the most enriched values observed in minerotrophic sites. Overall, we find that CH₄ emissions, CH₄ production pathway and C source are correlated with pH and flooding regime, and cannot be predicted by vegetation alone. Our improved understanding of these key relationships in tropical peatlands provides the foundation necessary for future upscaling of site-level methane emissions across the region.