Unexpectedly High Methane Emissions through Black Ash Lenticels in Forest Wetlands of Northern Michigan

Abstract:

Methane (CH₄) emissions from wetlands contribute 20-40% to the global CH₄ budget, and most research has focused on diffusive, ebullitive and plant-arenchyma mediated transport pathways in soils. Recent studies have shown considerable amounts of CH₄ to be emitted via the lenticel pathway. Forested wetlands cover approximately 9.9 million hectares in North America, and to our knowledge no study has previously compared emissions of CH₄ through soil and lenticel pathways in North American forested wetlands. Our objectives were to quantify the fluxes of CH₄ emissions via lenticels in black ash (Fraxinus nigra Marsh.) wetlands and evaluate some factors that may affect lenticel CH₄ emissions. We measured CH₄ emissions from nine black ash trees monthly during the 2014 growing season and compared the fluxes to those from collocated soil chambers in three forested wetlands in the Upper Peninsula of Michigan. During each sampling period, 15-mL samples were collected via syringe every ten minutes for a forty minute period. Water table depth, dissolved oxygen, air temperature, soil temperature, and lenticel density were recorded. Lenticel effluxes were up to 4.5 times greater than the soil effluxes and that water table position was correlated with soil and lenticel gas fluxes. We conclude CH₄ emissions from forested wetlands may be considerably underestimated and our findings highlight the need for the inclusion of lenticel gas emissions in global estimates and Earth Systems Models.