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Artyukhov et al. Carbon Footprints 2026, 5, 8 Page 5 of 21

Table 1. Characteristics of sampling landscapes and soil classification
Site code Coordinates Landscape Soil (WRB, 2022)

Sal_C1 66.530222, 66.705972 Plain herb-moss- draft shrub forest-tundra Albic Podzol
RI_C2 66.872411, 65.397275 Mountain draft shrub-herb tundra Skeletic Cambisol
RI_C3 66.871350, 65.403931 Mountain lichen-shrub-herb tundra Skeletic Leptosol
RI_C5 66.866138, 65.411269 Intermountain moss-herb-shrub tundra Skeletic Cryosol
RI_C6 66.860714, 65.452812 Intermountain draft shrub-herb-moss tundra Histic Cryosol
Gk_C7 66.506902, 67.037746 Plain moss-draft shrub-shrub forest-tundra Cryic Histosol
Lb_C8 66.692222, 66.299444 Polygonal tundra Histic Cryosol
Ya_P1 67.860090, 70.501160 Plain polygonal dwarf shrub-lichen tundra Turbic Podzol
Ya_P2 67.859780, 71.091050 Plain polygonal dwarf shrub-lichen tundra Entic Podzol

WRB: World Reference Base for Soil Resources

dwarf shrubs Vaccinium uliginosum, Empetrum nigrum and Betula nana. The soils are formed on layered
sandy gleyed deposits. The first key site (Ya_P1) is located in the subzone of southern hypoarctic tundra near
lakes Ngevadyodato and Yakhadymalto, where Turbic Podzol is developing. The profile exhibits distinct
signs of cryoturbation, which are represented by a whirl-like pattern and the protrusion of the lower C
horizon into the upper gley horizon. The second key site (Ya_P2) is located next to the Yaroto lakes, where
Entic Podzol is forming. All sampling locations are generalized in Table 1.

Laboratory and data processing
Laboratory analyses included the determination of actual (pH H O) and exchangeable (pH KCl) acidity by
2
the potentiometric method [30,31] . Particle size distribution was defined by the method used by Kachinsky .
[32]
Total carbon content was measured by high-temperature dry combustion on a LECO TruSpec MICRO
elemental analyzer (model 630-300-200; St. Joseph, MI, USA) at the “Chemical Analysis and Materials
Research Center” of Saint Petersburg State University (SPbU) Research Park, according to the FAO
methodology . The studied soils contained no carbonates; therefore, the total carbon content was equated
[33]
to the soil organic carbon (SOC). The results of the basic physicochemical analyses for all soil horizons are
given in Supplementary Tables 1 and 2. Potentially mineralizable organic carbon (PMC) was determined in
topsoil horizons only (mostly 0-10 cm), as they represent the most biologically active part of the soil profile,
using the biokinetic fractionation method . For this purpose, 10 g of air-dry soil were placed in 50 mL glass
[34]
beakers and moistened to 25% moisture with distilled water. Subsequently, the samples were pre-incubated
in slightly open plastic containers in a dark place at 10 and 25 °C for 7 days. These temperatures were chosen
because 10 °C represents the mean air temperature in July at the YaNAO region, the most biologically
productive month, while 25 °C represents peak temperatures that have occurred more frequently in recent
years due to climate change [35,36] . After pre-incubation, a beaker with 10 mL of 0.1 mol/L NaOH was also
placed inside the airtight plastic container to absorb the CO released during carbon mineralization. Three
2
containers with NaOH solution without soil were used as blank samples. Thereafter, all samples were
incubated at 25 and 10 °C for 90 days; these temperatures correspond to those of the ambient air during the
summer months at the study areas and are also comparable to the duration of the frost-free period. During
the incubation process, the NaOH solution was periodically changed at 12, 36, and 84 h, and then on days 6,
13, 20, 27, 34, 43, 50, 63, 77, and 91 from the start of incubation. A standardized 0.05 mol/L HCl solution was
used to titrate the NaOH solution.

The rate of С-СО release (μg C-CO /g soil/h) during the exposure period was calculated according to :
[37]
2
2
1 1 1 (1)
= × × ( 0 − ) × 12.01 × × × 1000
2