Methane and carbon dioxide dynamics within four vernal pools in Maine, USA

Abstract

Vernal pools are small, seasonal wetlands that are a common landscape feature contributing to biodiversity in northeastern North American forests. Basic information about their biogeochemical functions, such as carbon cycling, is limited. Concentrations of dissolved methane (CH₄) and carbon dioxide (CO₂) and other water chemistry parameters were monitored weekly at the bottom and surface of four vernal pools in central and eastern Maine, USA, from April to August 2016. The vernal pools were supersaturated with respect to CH₄ and CO₂ at all sampling dates and locations. Concentrations of dissolved CH₄ and CO₂ ranged from 0.4 to 210 μmol L⁻¹ and 72–2300 μmol L⁻¹, respectively. Diffusive fluxes of CH₄ and CO₂ into the atmosphere ranged from 0.2 to 73 mmol m⁻² d⁻¹, and 30–590 mmol m⁻² d⁻¹, respectively. During the study period, the four vernal pools emitted 0.1–5.8 kg C m⁻² and 9.6–120 kg C m⁻² as CH₄ and CO₂, respectively. The production fluxes (production rates normalized to surface area) of CH₄ and CO₂ ranged from − 0.02 to 0.66 and 0.40–4.6 g C m⁻² d⁻¹, respectively, and increased significantly over the season. Methane concentrations were best predicted by alkalinity, ortho-phosphate and depth, while CO₂ concentrations were best predicted with only alkalinity. Alkalinity as a predictor variable highlights the importance of anaerobic respiration in production of both gases. Our study pools had large concentrations and effluxes of CH₄ and CO₂ compared to permanently inundated wetlands, indicating vernal pools are metabolically active sites and may be important contributors to the global carbon budget.