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Page 6 of 21 Artyukhov et al. Carbon Footprints 2026, 5, 8

where SMR is the rate of С-СО release; C is the concentration of the standard HCl solution used for
HCl
2
titration (mol/L); V 0 is the volume of HCl titrated in the blank sample (mL); V is the volume of HCl titrated
in the flasks containing soil (mL); t is the incubation time (h); and m is the mass of the soil (g).

The cumulative C-CO production (mg C-CO /g) was determined by summing the amount of carbon
2
2
released at each measurement interval with the sum of the previous intervals. To calculate the potentially
mineralizable organic carbon (PMC) content, the cumulative C-CO production curve over the entire
2
incubation period was approximated using a single first-order kinetic model according to :
[34]

= 0 × (1 − exp(− × )) (2)

where C is the cumulative content of С-СО (μg C-CO /g soil) for the time t (days); C 0 is the content of PMC
2
t
2
of SOM (μg C-CO /g soil); k is the constant for the rate of mineralization of the SOM (day );
-1
2
The temperature sensitivity of soil respiration was quantified using the Q function , which describes the
[38]
10
factor by which the respiration rate increases with a 10 °C rise in temperature. The Q values were calculated
10
based on the cumulative carbon mineralized (C 0) at 10 and 25 °C using :
[38]
10

2 2− 1
10 = (3)
1
where R and R are the respiration rates (or in this case cumulative C mineralized) at temperatures T 2
2
1
(25 °C) and T (10 °C), respectively.
1
Samples from each soil horizon were analyzed for the total content of Sr, Pb, Zn, Co, Ni, Cr, V, As, and MnО
by X-ray fluorescence spectroscopy using a Spectroscan Max-G spectrometer as described before .
[39]

The assessment of soil pollution levels was conducted using the total soil pollution index (Zc, Saet index), as
calculated using :
[40]

∑︁
= ( + . . . + ) − ( − 1) (4)

where K = C/C (2), and C and C are the background and actual contents of the i-th element in the soil,
ib
i
ki
ib
i
respectively.
In the calculation of Z , only accumulating elements were considered, and the boundary criterion K k(crit) > 2
c
was applied , where K k(crit) is the critical enrichment factor of the i-th element, defined as the ratio of the
[41]
element’s concentration in soil to its background value at which pollution effects become significant.
According to the soil pollution hazard assessment scale based on the total soil pollution index (Z ),
c
contamination levels are classified as acceptable (Z < 16), moderately hazardous (16 < Z < 32), hazardous
c
c
(32 < Z < 128), and extremely hazardous (128 < Z ) [42,43] .
c
c
As the background concentration of heavy metals, arsenic, and manganese oxide in the soils of northern
Western Siberia, data from Bely Island and the vicinity of the settlements of Novy Port and Ust-Yuribey were
used . The calculation of Z for soils from the Rai-Iz mountain massif (Polar Urals) was carried out
[44]
c
excluding the concentration values of Zn, Ni, Co, MnO, and Cr. The exclusion of these elements and
compounds was due to their abnormally high background concentrations, resulting from the rich
mineralogical composition of ultramafic rocks, which are widespread in the Polar Urals .
[45]