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Article

Monitoring the Permafrost Conditions along Pipeline Routes in Central Yakutia, Russia

by
Stepan Varlamov
1,
Pavel Skryabin
1,
Aleksandr Zhirkov
1,* and
Zhi Wen
2
1
Melnikov Permafrost Institute SB RAS, Yakutsk 677010, Russia
2
State Key Laboratory of Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources CAS, Lanzhou 730000, China
*
Author to whom correspondence should be addressed.
Land 2022, 11(12), 2331; https://doi.org/10.3390/land11122331
Submission received: 27 October 2022 / Revised: 8 December 2022 / Accepted: 12 December 2022 / Published: 19 December 2022
(This article belongs to the Special Issue Permafrost Landscape Response to Global Change)
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Abstract

:
Pipelines are critical infrastructure for Yakutia, transporting vital supplies to communities in this vast northern region. The pipeline routes in central Yakutia traverse areas of ice-rich permafrost that is sensitive to temperature changes. This study examined the thermal state of permafrost in undisturbed and disturbed settings along the Lena River to Mundulakh Reservoir water pipeline and the Mastakh to Yakutsk gas pipeline and considered the effects of climatic fluctuations and surface disturbances (forest removal and wildfire) over the monitoring periods of 28 and 18 years, respectively. The geocryological conditions in the study area, as well as the methods of permafrost thermal monitoring, are described. The observation results demonstrated significant increases in the mean annual ground temperature in the upper permafrost layers, as well as in the active-layer thickness following fire and post-fire clearing. At some sites, progressive deepening of the active layer caused the formation of taliks and reached the top of massive ground ice, initiating permafrost degradation. The development of extreme ground temperatures in the layer of annual temperature fluctuations was analyzed according to the combination of seasonal and annual meteorological conditions and the type of anthropogenic impact. The research results can be extrapolated to similar anthropogenic landscapes.

1. Introduction

Modern climate changes and the intensive development of cold regions pose urgent problems for geocryology. The stability of natural systems under modern climate warming and anthropogenic impacts is associated with the study of the patterns of changes in the permafrost zone. The thermal state of soils is one of the main factors that determine the stability of permafrost landscapes in the development of a territory.
Pipelines are critical for the safe, efficient, and cost-effective transport of materials and commodities in northern regions. However, they are often affected by the harsh environment and the presence of underlying permafrost. Pipeline construction is associated with surface disturbances, which can cause a deepening of the active layer and warming of the permafrost. With appropriate pipeline designs and mitigation measures, conditions tend to stabilize with time. Additionally, problems can be encountered during the operation phase as a result of the complex interaction between the pipeline and permafrost, which may include thaw settlement, frost heave, upheaval buckling, buoyancy, and slope instability [1,2,3,4,5,6,7,8,9,10]. Many of these issues can develop many years after construction in response to changes in the thermal regime of the right-of-way [11]. Permafrost–related operating hazards require ongoing monitoring because the nature and magnitude of the threat are constantly changing over time [12]. Successful monitoring programs have been maintained for major pipelines, such as the Norman Wells pipeline in Canada [13,14], the Trans-Alaska Pipeline System in Alaska [12], the China–Russia crude oil pipeline [8,9], and the Nadym to Pur-Taz gas pipeline in Russia [7].
Engineering geocryological monitoring is a system of long-term observations of spatial and temporal changes in the state of permafrost associated with climate change and anthropogenic impacts. Monitoring is especially important for long-distance linear pipeline infrastructure because the harsh environment causes more frost hazards, higher sensitivity of permafrost to temperature change, and the complex interaction between the pipeline and permafrost [11,15,16,17,18].
Gas pipeline safety issues in permafrost regions were addressed by [4,19,20] for the West Siberian petroleum province and by [21], among others, for the Canadian Arctic. Studies that dealt with the gas pipeline–permafrost interaction included those by [2,3,22,23]. They emphasized that information for assessing the condition of pipeline geotechnical systems should result from comprehensive field studies, as well as from the use of current satellite monitoring tools. Research on the pipeline–permafrost interaction should be accompanied by experimental field observations with the wide use of mathematical methods.
Climate warming of the globe is an established fact. Over recent decades in Central Yakutia, there has been a strong warming of air temperature, higher than in most regions of Russia [24,25]. However, the warming rates vary greatly over space and time. The permafrost response to recent climate change and variability also varies across permafrost regions due to many factors, including but not limited to altitude, topography, soil type, ice content, soil moisture, vegetation, snow cover, and anthropogenic surface disturbances [17,26,27,28].
The results of studies of the evolution of the thermal state of soils for the period between the III International Geophysical Year (1957/59) and the IV International Polar Year (2007/08) in Russia were summarized by [29]. Romanovsky et al. estimated the thermal state of permafrost in Russia over the past 20–30 years [30,31]. Changes in the thermal state of upper permafrost in Central Yakutia under natural conditions and anthropogenic impacts over the last 30–40 years were documented by [32,33,34,35].
This paper summarizes for the first time the results of long-term monitoring of permafrost sites along the western (Nizhnij Bestjakh–Mundulakh) section of the Lena-River-to-Tuora-Kyuel water pipeline and the Mastakh-to-Yakutsk gas pipeline (Figure 1). Monitoring of the above-ground, seasonally operating water pipeline has been carried out since 1993, while monitoring of the gas pipeline constructed in the 1960s was initiated in 2003 to examine the thermal effects of a wildfire that occurred in 2002. The research programs included studies of the permafrost distribution, composition, and temperature regime in the undisturbed and disturbed terrain along the pipelines in order to quantify the spatiotemporal variability of the thermal state of near-surface permafrost. This study was based on the field data obtained from these long-term observations.

2. Study Area and Methods

The pipeline routes traverse areas with difficult surface and ground conditions, including the presence of continuous permafrost, suprapermafrost water, massive ground ice, and extensive taliks, as well as the widespread occurrence of frost-related landforms and processes [36,37]. In the study area, the permafrost terrains crossed by the pipelines include a floodplain, sand ridges comprising the middle alluvial terraces, and inter-alas terrain on the upland (Table 1). The inter-alas type of terrain occupies watershed spaces between alas depressions, where larch forests are widespread on sandy-loamy ice-rich soils.
Landscape and monitoring methods were used as the basis for long-term studies of the thermal regime of soils, the parameters of which varied in seasonal and annual cycles. Landscape surveys were conducted to identify representative terrain types for the selection and establishment of ground thermal regime study sites.
Monitoring for the Lena River–Tuora-Kyuel water pipeline project was initiated in 1993 in the western section of the proposed route between Nizhnij Bestjakh and Mundulakh (see Figure 1). Five sites were established in the floodplain, sand ridge, and inter-alas terrain types for observations of the ground temperature, surface settlement, active-layer thickness, and snow depth. In order to observe the temperature regime of soils within the annual heat turnover layer, boreholes with a depth of 12 m were drilled and equipped with instruments at each site, to measure the ground temperatures at depths of 0.5, 1, 2, 3, 4, 6, 8, and 10 m. Information on surface and subsurface conditions, including the lithology, ice content, gravimetric moisture content, bulk density, and thermal conductivity, was collected during drilling.
The ongoing observations at monitoring sites include measurements of ground temperatures in boreholes, active-layer thickness at the end of the thaw season, and snow depth during the period of maximum snow accumulation. Additionally, the restoration of the vegetative and organic covers in the disturbed areas, as well as the development of cryogenic processes and forms, are documented (see Table 1).
Permafrost monitoring along the Mastakh–Yakutsk gas pipeline was started in 2003 to study the thermal effects of fire and the removal of burned forest. Two sites (forest and burn) were established at locations representing the inter-alas terrain type with 15 m-deep boreholes for temperature measurements (see Figure 1). The observation program and measurement frequency are similar to those at the water pipeline sites.
The focus of this research was the layer of annual heat gains and losses, i.e., the upper 10–15 m of the ground subjected to annual temperature cycles. The main thermal parameters that may be used as indicators of the thermal evolution of upper permafrost layers in the context of modern climate warming are the depth of seasonal thaw (ξ), mean annual temperature at the bottom of the active layer (Tξ), and mean annual temperature at the depth of zero annual amplitude (T0).
Ground temperatures were measured with MMT-4 semiconductor thermistors (made at the Melnikov Permafrost Institute). Thermistor cables were installed permanently in the boreholes backfilled with drill cuttings. Temperatures were recorded by measuring the thermistor resistance using a portable digital multimeter with a resolution of 0.1 ohms. This method, with the lead resistance accounted for, generally gives a temperature error of 0.05 °C, which is acceptable for the scale and status of the present study. The active-layer thickness was measured using mechanical probing with a metal rod and a soil auger.
The method of conducting geothermal monitoring showed its reliability and can be successfully used in different natural and climatic conditions. Analysis and summary of observation results at various stages of monitoring are presented in our earlier publications [36,37].

3. Results and Discussion

Recent Climatic Changes

The climate of Central Yakutia is determined by its location deep in Asia’s interior, in the vast Lena–Vilyui depression that is sheltered, except in the northwest, by mountains and uplands from warm, humid air masses from the Atlantic and Pacific. The winter climate is dominated by an extension of the Siberian High. The summer climate is affected by anticyclones moving from the north; a ridge of high pressure from the Sea of Okhotsk; and intrusions of cyclones from the west, northwest, and south [38].
Regarding its winter temperatures, annual temperature range, and continentality index, the region has no analogs elsewhere in Russia, except for Oymyakon and Verkhoyansk. The mean air temperature for the cold season (210–215 days below 0 °C) is −26 °C and the mean temperature for the warm season (150–155 days above 0 °C) is approximately 12 °C. The mean annual precipitation ranges from 250 to 300 mm, of which 160 to 200 mm falls as rain during the summer months. Peak precipitation occurs in the second half of summer. Winter precipitation is low, with a late winter snow depth of only 25–40 cm. The snow density varies little and is 170–200 kg/m3 by the end of winter. The snow cover duration, based on Yakutsk meteorological station data, is about 200 days [39]. Therefore, the study area has an extremely continental climate characterized by large annual and daily temperature ranges and low precipitation.
There is no consensus among researchers on the level of air temperature changes in the 21st century. Projections made by the Voeykov Main Geophysical Observatory based on the extrapolation of climatic characteristics suggest that the observed increasing trend in Russian mean annual air temperature will be maintained and increase by 1.5 °C by 2030 as compared with the year 2000 values [40]. Neradovsky and Skachkov predicted an increase of no more than 0.7–1.0 °C in 2050 above the current mean annual temperatures [41]. Of more concern are the changes in snow accumulation patterns, which have a significant influence on the ground thermal regime.
To analyze the variability and trends in the major climate variables (air temperature, precipitation, and snow depth) over the observation period, we used records from the Yakutsk meteorological station located nearest to the study areas. The mean annual air temperature at Yakutsk based on 1961–1990 normals was −10.0 °C, the mean annual precipitation was 235 mm, and the mean winter snow depth was 18.9 cm. Between 1980/1981 and 2020/2021, the mean annual air temperature increased by 2 °C and is now −8.0 °C, while the annual precipitation remained fairly unchanged (233 mm), with–some increase in mean snow depth (22 cm). The Yakutsk data show significant warming since the late 1960s, with a trend of 0.066 °C/year, which is greater than most regions in Russia. The second decade of the 21st century was the warmest (−7.2 °C) on record in Central Yakutia (Figure 2).
As seen in Table 2, the study period was characterized by significant interannual variations in air freezing and thawing indices, precipitation, snow depth, and snow-cover onset and end dates.
To qualitatively characterize the variability of climatic parameters, the boundary values of normal climatic conditions (Cn) can be expressed by the following inequality:
N a v − δ n ≤ C n ≤ N a v + δ n
where Nav is the arithmetic mean and δn is the standard deviation of this climate characteristic for the entire observation period.
If the values lie beyond the specified limits (±2δn), the parameters are classified as anomalous or extreme. The Cn range between ±δn and ±2δn can be characterized as intermediate: cold or warm, wet or dry, high or low, and late or early.
Thus, the temporal variability of climatic variables for the period 1981–2020 was classified into five types (Table 3):
For air temperature: anomalously cold ˂ Nav − 2δn ˂ cold ˂ Nav − δn ˂ normal ˂ Nav + δn ˂ warm ˂ Nav + 2δn ˂ anomalously warm;
For precipitation: anomalously dry ˂ Nav − 2δn ˂ dry ˂ Nav − δn ˂ normal ˂ Nav + δn ˂ wet ˂ Nav + 2δn ˂ anomalously wet;
For snow cover onset: anomalously late ˂ Nav − 2δn ˂ late ˂ Nav − δn ˂ normal ˂ Nav + δn ˂ early ˂ Nav + 2δn ˂ anomalously early;
For mean winter snow depth: anomalously low ˂ Nav − 2δn ˂ low ˂ Nav − δn ˂ normal ˂ Nav + δn ˂ deep ˂ Nav + 2δn ˂ anomalously deep.
Table
Table 3. Number of years and seasons by air temperature, precipitation, and snow cover types in the 20-year periods 1980/81–1999/00 (numerator) and 2000/01–2019/20 (denominator) based on Yakutsk Station data.
Table 3. Number of years and seasons by air temperature, precipitation, and snow cover types in the 20-year periods 1980/81–1999/00 (numerator) and 2000/01–2019/20 (denominator) based on Yakutsk Station data.
Air TemperaturePrecipitationSnow Cover
TypeAnnualWinterSummerTypeAnnualSummerTypeSnow Cover OnsetTypeSnow Depth
Anomalously cold0/01/01/0Anomalously dry0/10/0Anomalously late0/0Anomalously low0/0
Cold6/15/15/1Dry2/33/4Late5/2Low2/4
Normal14/1313/1212/13Normal16/1114/14Normal11/16Normal16/13
Warm0/61/72/6Wet2/43/2Early4/1Deep2/1
Anomalously warm0/00/00/0Anomalously wet0/10/0Anomalously early0/1Anomalously deep0/ 2
Figure 2 shows a statistically significant and persistent increasing trend in mean annual air temperature. This warming trend was primarily associated with warmer winter temperatures (October–April). The contribution of the summer months (May–September) was less significant [24]. The coldest and warmest years were 1986/87 and 2019/20, respectively; six years were cold (1981/82, 1982/83, 1984/85, 1987/88, 1993/94, and 2000/01); and five years were warm (2001/02, 2007/08, 2013/14, 2016/17, and 2018/19) (see Table 3).
As is seen in Figure 3, annual precipitation in Yakutsk demonstrated substantial interannual variability over the past decades, with a very slight decreasing trend over the 40-year period. Six years (1988/89, 1992/93, 2002/03, 2004/05, 2006/07, and 2012/13) were characterized as wet and the year 2005/06 as anomalously wet. The years 1985/86, 1991/92, 2001/02, 2003/04, and 2008/09 were dry and 2000/01 was anomalously dry (see Table 3).
Data for snow depth, as well as for snow cover onset and end dates, also exhibited strong interannual variability over the study period (see Table 3). The date of continuous snow cover onset was anomalously early in 2004; early in 1982, 1985, 1998, 1999, and 2010; and late in 1983, 1986, 1988, 1990, 1996, 2007, and 2016. The snow depth was anomalously deep in the winter of 2004/05 and 2005/06; deep in the winters of 1982/83, 1999/00, and 2006/07; and low in the winters of 1995/96, 1996/97, 2000/01, 2002/03, 2008/09, and 2009/10 (Figure 4).
It is seen from Table 3 that the hydrometeorological factors controlling the ground thermal regime experienced strong seasonal, annual, and interannual variability. The last two decades of the 20th century compared with the two decades of the current century were characterized by almost the same amount of Cn (14 and 13) and a predominance of cold winter, summer, and annual air temperatures, including one anomalously cold winter and one anomalously cold summer. In contrast, over the last two decades, there has been an increase in the number of warm winters, summers, and annual air temperatures. As for the annual precipitation, the last two decades of the last century were distinguished by a predominance in the amount of Cn (16 years) and 2 years each with wet and dry years; the two decades of the current century were distinguished by a decrease in the amount of Cn (11 years) due to an increase in the amount of dry (3) and wet (4) years and the appearance of anomalously dry (1) and anomalously wet (1) years. As for the summer precipitation, the considered decades had the same amount of Cn (14), 3 and 4 dry summers, and 3 and 2 wet summers of the past and present centuries, respectively. In terms of snow depth, the 1980s–1990s had 16 Cn, 2 shallow, and 2 deep snow winters, while the 2000s–2010s had 13 Cn, 4 shallow, 1 deep, and 2 anomalously deep snow winters.

4. Ground Thermal Conditions along Pipeline Routes

4.1. Water Pipeline

The route of the Nizhnij Bestjakh–Mundulakh water pipeline crosses three types of permafrost terrain: floodplain, sand ridge, and inter-alas terrain. In the floodplain type of terrain, thermal monitoring of permafrost was carried out in a forb-graminoid meadow in the middle floodplain (B–168/89). The surface was covered with 0.12 m-thick turf. The active layer consisted of fine sand to a depth of 1.5 m with a gravimetric moisture content of 18–21%. Permafrost with massive cryostructure consisted of fine- and medium-grained sands with a high ice content (0.42 as a decimal fraction) within the upper 12 m (Figure 5).
Observations at the floodplain site showed significant interannual variations in mean annual ground temperature, ranging from −1.1 to −3.5 °C at 10 m depth, and in the active layer thickness, ranging between 1.4 and 2.2 m. These fluctuations were associated with variability in snow conditions and the deposition of sand material by floods. The ground temperature was the lowest during the periods of anomalously low snowfall (1996–1998 and 2010–2013) when the maximum snow depth in March was only 30–35 cm. The highest ground temperatures were recorded in 1999–2001 and 2007–2008 when the snow cover was deeper than normal, reaching 40–50 cm (Figure 6).
As a result of severe floods in 2006 and 2011, a 0.3 m-thick layer of sand was formed on the floodplain surface. This led to a decrease in ground temperature by 1.6–2.0 °C (see Figure 6). Spring ice breakup on the Lena River was potentially dangerous in the area, not only because it was associated with ice jams but also because the stripping of trees and shrub vegetation by ice, sand deposition, flooding, and bank erosion led to changes in the ground thermal regime.
In the sand ridge terrain unit, thermal monitoring was conducted at two sites: one in undisturbed conditions and the other at a disturbed location. B-13/93 was an undisturbed site located in pine–lichen–bearberry forest. The ground surface at this site was covered by a 0.06 m-thick layer of poorly decomposed mosses and lichens with silty sands, having a moisture content of up to 12%. The active layer, 1.8 to 2.1 m in thickness, consisted of fine sands with very low moisture content in the upper 1 m (2–3%), increasing to 15–18% at its base. The underlying permafrost consisted of silty sands with massive cryostructure. The ice content was consistently high (0.36) down to a depth of 12 m (see Figure 5). The mean annual ground temperature at 10 m depth varied between −2.1 and −0.7 °C during 1993–2014 (see Figure 6), while the active layer thickness ranged from 1.85 to 2.10 m. The thermal regime of sands in the sand ridge terrain type was primarily controlled by the winter meteorological parameters (air temperature and snow cover dynamics), as well as by the low moisture content and low thermal conductivity of the active layer.
B-13/87 is a disturbed site where 10–15-year growth in the pine forest was destroyed in 1987 by a surface fire. The top 8 cm of soil contained burned vegetation remains and had moisture contents of 3–5%. Fine sands in the active layer had low moisture contents (5–13%) to a depth of 1.75 m. The perennially frozen fine sands had an ice content of 0.37 with no change with depth down to 12 m (see Figure 5). The wildfire caused an increase in mean annual permafrost temperature by 1.5 °C during the first four years. From the fifth year after the fire, the ground temperatures at the burn site with the desiccated soils in the active layer began to stabilize between −0.4 and −0.3 °C because of the unfavorable conditions of grass and shrub recovery (see Figure 6). This suggested later refreezing of the active layer and less cold storage due to the lower thermal conductivity of dry sands. The active layer thickness varied at the site between 2.4 and 2.8 m depending on the summer air temperature. Our earlier studies in similar settings (sites B-59/87 and B-1601) showed the formation of dry taliks, 20 to 30 m in thickness, in very dry sands (2–4%) [36]. Incipient water erosion features were observed on the slopes of the disturbed site. Thermal suffusion was reported to have developed in the adjacent areas.
In the inter-alas terrain type, ground thermal monitoring was initiated in 1993 at two sites along the Nizhnij Bestjakh–Mundulakh water pipeline. Site B-10/93 was at an undisturbed location in a larch–moss–mountain cranberry forest. The ground surface layer, 0.1 m or less in thickness, comprised green mosses from forest litter and had highly variable moisture content, ranging from 7 to 47%. The active layer was 1.4 to 1.6 m thick and consisted of silty sand and silt with moisture contents of 10–15%. The underlying frozen silts and silty sands had high moisture contents of 49–53% down to 3 m in depth. Core drilling showed the occurrence of wedge ice in the depth interval between 3 to 12 m (see Figure 5). The maximum snow depth varied between 31 and 36 cm over 27 years of observation (1993–2020). The mean annual ground temperature at the depth of zero annual amplitude (10 m) was increasing by 0.03 °C/year (see Figure 6 and Figure 7).
In 1992, a strip of land was cleared in a larch forest for a 1200 mm-diameter water pipeline supported on piles, concrete slabs, and wooden platforms. In 1993, a thermal monitoring section (B-12/93) was created on the pipeline right-of-way. The moisture content of the upper 0.05–0.1 m of disturbed soil fluctuated within a narrow range (4–9%). The active layer, consisting of silty sands, was characterized by a wide range of moisture contents (15–35%). Ice wedges occurred in the depth interval between 2.1 m and 14.0 m, which were underlain by silty sands with fine sand layers to a depth of 15.8 m and by fine sands to a 19 m depth (see Figure 5). Unfortunately, in the summer of 1995, the borehole was damaged. In September 2008, a new borehole was drilled to continue observations at a distance of 100 m from the first. Observations showed that the removal of shaded trees and insulating moss cover resulted in a strong increase in soil temperature. After 25 years, the soil temperature at the end of summer increased by 3.6 °C at a depth of 2 m and by 1.5 °C at a depth of 5 m (see Figure 6 and Figure 7). The soil warming trend was 0.052 °C/year, which was 1.9 times stronger than the trend in natural, undisturbed conditions. Thus, the pipeline supports were now located in warm, unstable permafrost with temperatures as high as −0.6 °C.
The mean annual ground temperature in borehole B-12/93* at a 5 m depth exceeded that in the undisturbed terrain (B-10/93) by 1.4 °C, and the active layer thickness increased by 1.1 m and reached 3.0 m. These thermal changes at the site where wedge ice occurred at depths close to the surface (1.6–2.4 m) caused permafrost degradation, resulting in surface subsidence by 0.5–1.0 m and thermokarst development (Figure 8). The formation of polygonal terrain along the pipeline may lead to instability of the supporting ground.
Thus, according to the results of many years of research, we quantitatively determined changes in the thermal regime of the soil in natural conditions and after disturbance along the water pipeline route.

4.2. Gas Pipeline

The Mastakh–Yakutsk trunk gas pipeline crosses permafrost terrain with difficult geotechnical conditions. Depending on the subsurface conditions, one of three modes of pipeline placement—elevated, buried, or surface—was selected. The buried mode was used between Mastakh and Yakutsk as a more reliable option, protecting the pipeline from the adverse impact of external factors. However, geocryological studies reported the development of hazardous processes, such as settlement and frost heave, in various landscapes, threatening the structural integrity and safety of the pipeline. The effect of wildfires and forest removal on permafrost conditions along the pipeline route is described below.
In 2003, two sites were established in an inter-alas area between the Kenkeme and Lena Rivers to monitor changes in the ground thermal regime, one in an undisturbed birch–larch forest stand (B-1/03) and the other at a disturbed site (B-2/03) where a 2002 surface fire burned out the surface vegetation and caused subsequent decay of the tree stand. Permafrost in the area consisted of ice-rich silty and muddy fine-grained sands with interbeds of silty sand and silt (see Figure 5). In the forest, the moisture content of the 0.14 m-thick forest litter varied from 34 to 46%; the sandy silts in the active layer had low moisture contents within 4–7%. The active layer thickness was 1.25 m. The ice content of the underlying permafrost was 0.30–0.33 as a decimal fraction.
Silty fine-grained sands interbedded with sand silt in the upper part of the active layer were wetter (7–17% moisture content) in the burned site compared with the forest. After the fire, suprapermafrost water was formed at 0.70 m from the surface due to intensive permafrost degradation. The active layer thickness increased to 1.78 m. The ice content of the underlying permafrost consisting of fine sands with interbeds of sandy silt and charcoal was 0.30.
During the 7 years following the fire, permafrost temperatures increased both at the forest and burn sites and reached the peak by the year 2008/2009 when the ground temperatures at a 10 m depth were 2.5–2.7 °C higher. Analysis of the meteorological data indicated that the period between 2002/03 and 2019/2020 had three warm years and one anomalously warm year in terms of air temperature, and three wet years, one dry year, and one anomalously wet year in terms of precipitation. The snow cover was characterized as anomalously deep for two winters, deep for one winter, and shallow for three winters. Afterward, the ground temperature at the forest site began to lower, with a 1.4 °C decrease by 2011, and remained fairly stable, with its values in the range of −2.7 to −3.1 °C. At the burn site, the ground temperature stabilized after 2010 due to shrub regrowth, with some variations between −1.6 and −1.2 °C (Figure 9). The late summer 2020 temperature profile for the forest site showed that the soil temperatures had almost recovered to the level of 2003 when the minimum values were recorded. At the burn site, the 2020 soil temperatures at depths of 1, 2, 3, 4, and 5 m were 2.7, 1.3, 0.6, 0.4, and 0.2 °C higher, respectively, compared with 2009, i.e., the upward trend in soil temperature continued (Figure 10).
The natural, undisturbed site experienced an increase in active layer thickness by 0.9 m between 2003 and 2009. This period was characterized by (1) alternating warm and normal years in terms of the mean annual air temperature; (2) three wet years and one anomalously wet year in terms of annual precipitation; and (3) two winters of anomalously deep snow cover, one winter with deep snow, and one winter with low snow. Moreover, suprapermafrost water began to form in the active layer due to thawing of the ice-rich permafrost. Afterward, the active layer thickness gradually recovered until 2015 and reached 1.0 m by 2016–2020 (Figure 11). In the burned and cleared area, the active-layer thickness in 2008 was almost about three times the pre-fire value. A 0.8 m-thick talik developed beneath the 2.3–2.4 m seasonally frozen layer in 2005–2009. The talik froze up during the winters of 2010–2012 with low snow, but the warm years of 2013–2016 resulted in a thin talik, which refroze in 2017–2018 and reappeared in 2019–2020 (see Figure 11). The meteorological conditions of the cold and warm seasons played a significant role in the formation of the talik. The results of the experiment showed that the thermal regime of the soil at the fire site and in the forest developed in different ways.

5. Conclusions

  • Quantitative estimates were obtained for the thermal dynamics of the upper permafrost in natural and disturbed terrain along the pipelines.
  • Analysis of the data from the Yakutsk meteorological station and the experimental monitoring sites indicated that the characteristics of meteorological conditions were some of the main factors that determined the multidirectional influence on the ground thermal regime. Climatic records for the period 1980–2020 showed a consistently increasing trend of 0.066 °C/year for air temperature and a substantial interannual variability of precipitation and snow cover parameters.
  • Removing the forest and surface cover along the elevated water pipeline increased the mean annual ground temperature at a 5 m depth by 1.5 °C and deepened the active layer by 1.1 m after 25 years. Changes in the ground thermal conditions resulted in surface subsidence by 0.5–1.0 m and thermokarst initiation, posing a threat to the stability of the supporting ground.
  • Forest removal at the fire site near the buried gas pipeline increased the mean annual ground temperature at a 10 m depth by 2.7 °C after 18 years. The surface disturbance created an unfrozen talik layer to a depth of 3.2 m beneath the active layer of 2.3–2.4 m. Surface subsidence was observed at the site, which suggested the initiation of polygonal terrain development.
  • The research results can be extrapolated to similar anthropogenic landscapes and can be used to model the thermal regime of the soil under anthropogenic impacts and develop environmental protection measures.

Author Contributions

Conceptualization, S.V. and P.S.; methodology, P.S.; software, S.V.; validation, S.V., P.S. and A.Z.; formal analysis, A.Z. and Z.W.; investigation, S.V.; resources, P.S.; data curation, S.V.; writing—original draft preparation, P.S.; writing—review and editing, Z.W.; visualization, A.Z.; supervision, P.S.; project administration, A.Z.; funding acquisition, A.Z. and Z.W. All authors have read and agreed to the published version of the manuscript.

Funding

Support for the long-term permafrost thermal monitoring was provided by the Melnikov Permafrost Institute, Siberian Branch of the Russian Academy of Sciences, as part of its fundamental research program no. АААА-А20-120111690010-2. The manuscript was prepared with financial support from the Russian Foundation for Basic Research (grant no. 20-55-53036) and Natural Science Foundation of China (grant no. 42011530084), as well as from the Chinese Academy of Sciences President’s International Fellowship Initiative (grant no. 2022VEB003).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Land 11 02331 g001 550
Figure 1. Map and photos of the study area showing monitoring sites and pipelines.
Figure 1. Map and photos of the study area showing monitoring sites and pipelines.
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Figure 2. Long-term course of the mean annual air temperature (°C) in Yakutsk, 1981–2020. The dotted line indicates a linear trend.
Figure 2. Long-term course of the mean annual air temperature (°C) in Yakutsk, 1981–2020. The dotted line indicates a linear trend.
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Figure 3. Long-term variation in the annual precipitation (mm) at Yakutsk, 1981–2020. The dashed line indicates a linear trend.
Figure 3. Long-term variation in the annual precipitation (mm) at Yakutsk, 1981–2020. The dashed line indicates a linear trend.
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Figure 4. Long-term variability of the mean winter snow depth at Yakutsk, 1981–2021. The dashed line indicates a linear trend.
Figure 4. Long-term variability of the mean winter snow depth at Yakutsk, 1981–2021. The dashed line indicates a linear trend.
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Figure 5. Borehole logs from floodplain (B-168/89), sand ridge (B-13/87, B-13/93), and inter-alas (B-10/93, B-12/93, B-1/03, B-2/03) terrain units. Lithology: (1) turf, (2) medium sand, (3) fine sand, (4) poorly sorted sand, (5) peat, (6) silty sand, (7) silt, (8) small pebbles, (9) mud. Cryostructure: (10) massive, (11) crustal, (12) layered, (13) ice. Other notations: (14) permafrost table.
Figure 5. Borehole logs from floodplain (B-168/89), sand ridge (B-13/87, B-13/93), and inter-alas (B-10/93, B-12/93, B-1/03, B-2/03) terrain units. Lithology: (1) turf, (2) medium sand, (3) fine sand, (4) poorly sorted sand, (5) peat, (6) silty sand, (7) silt, (8) small pebbles, (9) mud. Cryostructure: (10) massive, (11) crustal, (12) layered, (13) ice. Other notations: (14) permafrost table.
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Figure 6. Interannual variations in mean annual ground temperature at a 10 m depth along the water pipeline. B-168/89—forb meadow on a floodplain, B-13/93—pine forest on a sand ridge, B-13/87—burn and cut site on a sand ridge, B-10/93—larch forest in an inter-alas area, B-12/93—cut site in an inter-alas area.
Figure 6. Interannual variations in mean annual ground temperature at a 10 m depth along the water pipeline. B-168/89—forb meadow on a floodplain, B-13/93—pine forest on a sand ridge, B-13/87—burn and cut site on a sand ridge, B-10/93—larch forest in an inter-alas area, B-12/93—cut site in an inter-alas area.
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Figure 7. Ground temperature extremes in an undisturbed larch forest (B-10/93) and a water pipeline right-of-way (B-12/93).
Figure 7. Ground temperature extremes in an undisturbed larch forest (B-10/93) and a water pipeline right-of-way (B-12/93).
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Figure 8. Early stage of thermokarst, August 2009. View from the old damaged borehole B-12/93 (in front of the lake). New Borehole B-12/93* in the background (near the rig).
Figure 8. Early stage of thermokarst, August 2009. View from the old damaged borehole B-12/93 (in front of the lake). New Borehole B-12/93* in the background (near the rig).
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Figure 9. Variation in the mean annual ground temperature at 10 m depth in the birch–larch stand (B-1/03) and the burned/cleared site (B-2/03) in the inter-alas terrain type along the Mastakh–Yakutsk gas pipeline. Post-fire succession stages: grass (2003–2008), birch–shrub (2009–2014), and birch–larch (after 2015).
Figure 9. Variation in the mean annual ground temperature at 10 m depth in the birch–larch stand (B-1/03) and the burned/cleared site (B-2/03) in the inter-alas terrain type along the Mastakh–Yakutsk gas pipeline. Post-fire succession stages: grass (2003–2008), birch–shrub (2009–2014), and birch–larch (after 2015).
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Figure 10. Maximum (2009, red), minimum (2003, blue), and 2020 values (green) of the ground temperature in the larch forest (b-1/03) and the burned/cleared site (b-2/03) in the inter-alas terrain type along the Mastakh–Yakutsk gas pipeline.
Figure 10. Maximum (2009, red), minimum (2003, blue), and 2020 values (green) of the ground temperature in the larch forest (b-1/03) and the burned/cleared site (b-2/03) in the inter-alas terrain type along the Mastakh–Yakutsk gas pipeline.
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Figure 11. Variation in the seasonal thaw depth in the forest and the burned/cleared site in the inter-alas terrain type along the Mastakh–Yakutsk gas pipeline.
Figure 11. Variation in the seasonal thaw depth in the forest and the burned/cleared site in the inter-alas terrain type along the Mastakh–Yakutsk gas pipeline.
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Table
Table 1. Permafrost thermal monitoring sites.
Table 1. Permafrost thermal monitoring sites.
Terrain TypeBorehole IDMonitoring Start YearObservational Program
FloodplainB-168/891989Terrain survey, cryolithology, geocryological processes, meteorological conditions (based on weather station data), snow depth and density, thermophysical properties of surface covers and soils, and geothermal monitoring (permafrost temperature and seasonal thaw depth)
Sand ridgeB-13/87, B-13/931987, 1993
Inter-alasB-10/93, B-12/931993
B-1/03, B-2/032003
Table
Table 2. Annual and seasonal characteristics of air temperature, precipitation, and snow cover parameters for the period from 1980/81 to 2019/20 (based on Yakutsk station data).
Table 2. Annual and seasonal characteristics of air temperature, precipitation, and snow cover parameters for the period from 1980/81 to 2019/20 (based on Yakutsk station data).
Parameter.MeanMin.Max.δ
Air Temperature
Annual, °C−8.4−10.76.01.18
Sum for the cold season, month degrees−166.0−193.8−144.712.17
Sum for the warm season, month degrees65.855.972.54.24
Precipitation
Annual, mm23512534847.89
Warm season, mm1588225544.14
Snow Cover
Snow depth, cm21.911.936.45.50
Snow-cover onset (δ, days)Oct 13Sep 29Oct 247 days
Snow-cover end (δ, days)Apr 26Apr 18May 65 days
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Varlamov, S.; Skryabin, P.; Zhirkov, A.; Wen, Z. Monitoring the Permafrost Conditions along Pipeline Routes in Central Yakutia, Russia. Land 2022, 11, 2331. https://doi.org/10.3390/land11122331

AMA Style

Varlamov S, Skryabin P, Zhirkov A, Wen Z. Monitoring the Permafrost Conditions along Pipeline Routes in Central Yakutia, Russia. Land. 2022; 11(12):2331. https://doi.org/10.3390/land11122331

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Varlamov, Stepan, Pavel Skryabin, Aleksandr Zhirkov, and Zhi Wen. 2022. "Monitoring the Permafrost Conditions along Pipeline Routes in Central Yakutia, Russia" Land 11, no. 12: 2331. https://doi.org/10.3390/land11122331

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