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Harvard Forest REU Symposium Abstract 2023
- Title: Analysis of Temperate Forest Methane Dynamics under Soil Moisture Limited Evapotranspiration Regimes
- Author: Sam Anthony Jurado (Cornell University)
- Abstract:
Methane is an important greenhouse gas that accounts for 42% of atmospheric warming since the pre-industrial period. While biogenic methane (CH4) emissions are thought to be of a similar magnitude to anthropogenic emissions, they remain the largest source of uncertainty in the global CH4 budget which impedes our ability to predict climate change. The methane dynamics of some environments, such as the temperate forests of the Northeastern United States (NEUS), are highly dependent on soil moisture availability. We predict that as a result of more extreme precipitation patterns, NEUS land-atmosphere interactions will increasingly fall within a soil moisture limited transitional evapotranspiration regime (SL-T) and promote positive soil moisture-precipitation feedbacks. These positive feedback loops may make NEUS soils more dependent on synoptic scale storms to provide moisture to the system. Since dry soils do not sequester methane as efficiently as moist soils, we anticipate that longer dry periods and more intense bursts of rain will limit the diffusion of methane into the soil. We employed the mixed Bowen ratio method - in which vertical concentration gradients of a target gas are multiplied by the known eddy diffusivity of a tracer gas - to calculate methane gradient fluxes for the growing season (JJAS) of the years 2022 - 2023. Evolving correlations between evaporative fraction (EF) and soil moisture were sorted into three evapotranspiration regimes: a sensible heat dominated dry regime, a transpiration dominated buffer regime, and a transitional regime leading to energy limited surface interactions. Results indicate that forest transpiration may have a major impact on land-atmosphere coupling strength that undermines the development of increasingly arid positive soil moisture-precipitation feedback loops and promotes the sequestration of methane within the buffer regime.
- Research Category: Forest-Atmosphere Exchange
