Atmospheric methane consumption and non-native earthworms in northern forest soils

Background/Question/Methods

Soils in temperate forests consume atmospheric methane, but the amount depends on many factors, including land use, climate, and soil pollution. Less is known about the impact of non-native earthworms, which are currently invading many northern forests in the USA and Canada, consuming the forest floor layer, and altering soil structure. I surveyed methane dynamics in earthworm impacted and control soils in central New York State for 1) concentrations in soil air spaces, 2) fluxes between soil and the atmosphere using static chambers in the field, and 3) oxidation kinetics in the laboratory. An inert tracer gas SF6 was used to assess earthworm impacts on soil gas permeability. I expected less consumption of atmospheric methane in earthworm-impacted soils for several reasons, including soil mixing that would disturb the fine zonation of methane-oxidizing bacteria typically found in the mineral soil. 

Results/Conclusions

I found significantly greater concentrations of atmospheric methane within the profile of earthworm impacted soils than in controls, and sporadic measures of concentrations greater than atmospheric suggest that earthworms promote net methane production. Control soils were significantly more permeable to SF6, indicating that earthworm activity compacts forest soils. Consumption rates of atmospheric methane were statistically similar for earthworm impacted and control soils in the field. However, earthworm impacted soils consumed less methane when incubated in the laboratory, suggesting that the forest floor layer reduces the rate of atmospheric methane consumption in the field. The results extend the evidence that invasive earthworms in northern forests have an impact on atmospheric greenhouse gases to include atmospheric methane.