Controls on Carbon Gas Fluxes From a Temperate Forest Soil

Abstract

Forest soils consume atmospheric methane (CH4), serving as a major global CH4 sink that uptake an estimated 22 ± 12 Tg of CH4 per year. Temperature and soil moisture have been identified as key controls of the microbial consumption of CH4 in forest soils. Climate-driven warming and changing moisture regimes may impact forest soils’ role in the carbon cycle, and recent works suggests that forests could become weaker CH₄ sinks. Long-term monitoring sites can capture these changes, leading to better predictions of CH4 exchange between the atmosphere and soils under climate change. This study utilizes a long-term trace gas dataset from College Woods in Durham, NH, USA to track both CH4 and carbon dioxide (CO2) fluxes between 1989 and 2021. Between 1989 and 2001 gas fluxes were measured approximately biweekly. In June 2021 the site was re-established, and we collected weekly flux measurements at three collars on a hillslope and three collars in a hollow. Flux measurements collected June-October 2021 in College Woods indicated that average CH4 uptake in these soils was 3.27 ± 1.16 mg m-² d-1. This is consistent with the 3.35 ± 1.68 mg m-² d-1 average uptake rate observed June-October 1989-2001. Average CO₂ emissions from June -August 2021 were 2.86 ± 0.91 µmol m2s-1, also consistent with the 3.96 ± 2.36 µmol m2s-1 average for 1989-2001. We did not observe a significant change in carbon fluxes across the study period, in contrast with the recent studies suggesting the global forest soil CH4 sink is decreasing