Evaluating greenhouse gasses fluxes from soils to the atmosphere using chamber method

This research work is dedicated to studying the fluxes of carbon-containing greenhouse gases (CO₂ and CH₄) in the future carbon polygon area in Voyeykovo. The study aims to quantitatively assess the fluxes of these gases by the soil during the autumn period using the chamber method, as well as to identify the factors influencing their dynamics. The relevance of the work is determined by the significant role of greenhouse gases in the global carbon cycle and their substantial impact on climate change.

Methane (CH₄) and carbon dioxide (CO₂) are key greenhouse gases. Despite its lower atmospheric concentration, methane has a global warming potential 21 times higher than that of CO₂ over a 100-year period. The primary natural sources of CH₄ are wetlands and swampy areas, contributing up to 30% of the global emissions of this gas. Carbon dioxide, whose atmospheric concentration reached 428 ppm by 2025, is mainly released from soils as a result of microbial decomposition of organic matter and plant root respiration. The chamber method was used to measure gas fluxes, which involves isolating a soil area with a sealed chamber and subsequently recording changes in gas concentrations using a high-precision LI-COR gas analyzer (LI-7810).

Experimental studies were conducted in September and October 2024 across eight sites with varying soil types and vegetation: former agricultural lands, slopes with young trees, and wetland areas. Key soil parameters—temperature, moisture, and pH levels—were recorded before measurements. The measurement errors for CO₂ and CH₄ were within 5–10% and 4–7%, respectively.

Analysis of the results revealed several important patterns. First, a significant increase in greenhouse gas fluxes was observed during autumn. The average CO₂ emissions rose from 389 g/(m²·year) in September to 973 g/(m²·year) in October and 1826 g/(m²·year) in November. Similarly, CH₄ fluxes increased from 0.25 g/(m²·year) in September to 0.77 g/(m²·year) in October and 0.92 g/(m²·year) in November. This trend is attributed to the decline in plant photosynthetic activity in autumn, which reduces CO₂ absorption, as well as ongoing microbial activity in the soil due to accumulated summer heat.

Second, the highest CO₂ emissions were recorded on former agricultural lands (e.g., 2207 g/(m²·year) in October at site СР4), which is linked to the presence of labile carbon forms readily involved in microbial metabolism. Wetland areas (СР2, СР9) exhibited lower CO₂ fluxes but acted as sources of CH₄, with peak values of 0.4 g/(m²·year). The other sites showed CH₄ absorption, driven by the activity of methanotrophic bacteria.

Third, a dependence of gas flux intensity on soil acidity was identified. An increase in pH within the range of 7.0–8.7 correlated with higher emissions of both CO₂ and CH₄, consistent with existing literature. Additionally, by late autumn, the variability in flux values increased—up to 17-fold for CO₂ and 34-fold for CH₄. This may be due to strong diurnal temperature fluctuations, which modulate the activity of soil microorganisms.

This work contributes to understanding the role of boreal ecosystems in the global carbon cycle and can be used to develop strategies for managing carbon polygons.