Advances in thermokarst lake research in permafrost regions

FuJun Niu, GuoDong Cheng, Jing Luo,3, ZhanJu Lin

1. State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, Gansu 730000, China

2. Key Laboratory of Highway Construction & Maintenance Technology in Permafrost Region, Ministry of Transport, First Highway Consultants Co. Ltd. of China Communications Construction Company, Xi’an, Shaanχi 710075, China

3. University of Chinese Academy of Sciences, Beijing 100049, China

Advances in thermokarst lake research in permafrost regions

FuJun Niu1,2*, GuoDong Cheng1, Jing Luo1,3, ZhanJu Lin1

1. State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, Gansu 730000, China

2. Key Laboratory of Highway Construction & Maintenance Technology in Permafrost Region, Ministry of Transport, First Highway Consultants Co. Ltd. of China Communications Construction Company, Xi’an, Shaanχi 710075, China

3. University of Chinese Academy of Sciences, Beijing 100049, China

A thermokarst lake is defined as a lake occupying a closed depression formed by ground settlement following thawing of ice-rich permafrost or the melting of massive ice. As it is the most visible morphologic landscape developed during the process of permafrost degradation, we reviewed recent literature on thermokarst studies, and summarized the main study topics as: development and temporal evolution, carbon release, and ecological and engineering influence of thermokarst lakes. The climate warming, forest fires, surface water pooling, geotectonic fault and anthropogenic activity are the main influencing factors that cause an increase of ground temperatures and melting of ice-rich permafrost, resulting in thermokarst lake formation. Normally a thermokarst lake develops in 3-5 stages from initiation to permafrost recovery. Geo-rectified aerial photographs and remote sensing images show that thermokarst lakes have been mainly experiencing the process of shrinkage or disappearance in most regions of the Arctic, while both lake numbers and areas on the Qinghai-Tibet Plateau have increased. Field studies and modeling indicates that carbon release from thermokarst lakes can feedback significantly to global warming, thus enhancing our understanding of the influences of thermokarst lakes on the ecological environment, and on regional groundwater through drainage. Based on field monitoring and numerical simulations, infrastructure stability can be affected by thermal erosion of nearby thermokarst lakes. This review was undertaken to enhance our understanding of thermokarst lakes, and providing references for future comprehensive studies on thermokarst lakes.

thermokarst lake; permafrost; ground ice; environment; engineering influence

1 Introduction

Permafrost regions occupy about 25% of the earth terrestrial surface (Nelson, 2003). In the Northern Hemisphere, these regions occupy extensive areas of the Arctic, high-elevation terrain of the mid-latitude plateau (Qinghai-Tibet Plateau (QTP)), and high mountain ranges, where mean annual air temperature (MAAT) is lower than 0 °C. It is believed that permafrost has undergone degradation due to climate warming over the past few decades (Jorgensonet al., 2001; Yanget al., 2010). Permafrost degradation always show as increase of ground temperature and active-layer thickness (Jinet al., 2006, 2008), and decrease of permafrost thickness and distribution areas. During the degradation process, the topography ischanged in micro- and macro-scales, normally showing ground surface settlement (van Everdingen, 2005). One of the most significant scenery is the thermokarst lake (Figure 1), which occupies a closed depression formed by ground settlement following the thawing of ice-rich permafrost or melting of massive ice (Herbert, 1997). In recent years, thermokarst lakes have received much attention as they generally cause soil erosion and shape permafrost landscapes (Czudek and Demek, 1970; Burn and Smith, 1990; Arpet al., 2011; Morgensternet al., 2011), influence local infrastructure (Linet al., 2009, 2012), change the regional ground water discharge, resulting in local ecosystem change (Carter, 1996; Yoshikawa and Hinzman, 2003; Osterkampet al., 2009; Pohlet al., 2009; Karlssonet al., 2012), and release carbon preserved in the permafrost, thereby providing feedback to global warming (Phelpset al., 1998; Walteret al., 2006, 2007; Schuuret al., 2009; Zonaet al., 2009; Karlssonet al., 2010). Most of these studies were carried out in Arctic and sub-Arctic regions. In China, though thermokarst lakes were mentioned in reference to their influence on infrastructures in the QTP around 30 years ago (Wanget al., 1979), detailed studies were lacking until recently (Linet al., 2009, 2010, 2011a; Niuet al., 2011). These recent studies are mainly concerned with thermokarst lake development, and their influence on the permafrost regime and nearby infrastructures. This paper summarizes recent literature on thermokarst lake studies, and to provide an over view of thermokarst lakes such as: (1) development, (2) temporal evolution, (3) carbon release and (4) engineering, environmental and ecological influences. Also, this paper provides references of thermokarst studies in the permafrost regions of the QTP.

Figure 1 Thermokarst lake scenery in different permafrost regions. Thermokarst lake development in (a) Yakutsk, Siberia, (b) Yukon, Canada, (c) Qinghai-Tibet Plateau, China, and (d) thermokarst pond development in northeast China caused by engineering excavation

2 Development of thermokarst lakes

2.1 Factors and process contributing to thermokarst lake development

Thermokarst lakes generally form from the thawing of ice rich permafrost, which can result by external natural disturbance, such as forest fires and climatic warming (Burn and Smith, 1990; Burn, 2002; Yoshikawa and Hinzman, 2003) or anthropogenic activity (Linet al., 2010), and these factors are generally compounded and interactive (Murton, 2009). Due to the low albedo and high heat storage capacity of gathering water in the disturbed area (Yoshikawa and Hinzman, 2003; Gooseffet al., 2009; Murton, 2009), solar radiation will heat lake water and thereby warmthe underlying permafrost. Once the thermokarst lake forms, the process of convective heat flux from moving water at the lake bottom will result in the continuous thawing of permafrost beneath the lake bottom until the talik forms (Linet al., 2010). Burn (2002, 2005) pointed out that the formation of taliks at the lake-bottom is closely related to water depth and maximum ice thickness. If the water depth is larger than maximum ice thickness, and mean annual lake-bottom temperature is greater than 0 °C, a talik will exist beneath the lake bottom throughout the winter, while if the water depth is less than maximum ice thickness, no talik will form below the lake bottom (Ling and Zhang, 2003; Linet al., 2010, 2011a). The development of the talik maybe stopped when the ground thermal regime is in equilibrium with the lake bottom temperature (Johnston and Brown, 1964, 1966; Smith, 1976; Burn, 2002). In addition, ground ice content also has a large effect on thermokarst lake depth (Hopkins, 1949; Hopkinset al., 1955). The modeled results of West and Plug (2008) indicated that thermokarst lake basins generally achieve a depth of about 20 m in deep ground ice environments, while in shallow ground ice settings, lakes are less than 3 m deep.

The lateral expansion of thermokarst lakes is mainly affected by the thawing of ice-rich permafrost underneath the shoreline that lead to accelerated shoreline collapse and thaw slump activity (Kokeljet al., 2009). There are numerous processes that can contribute to lateral lake expansion, including: wind-driven circulation resulting in the thermo-mechanical erosion of ice-rich permafrost in the lakeshore (Carson and Hussey, 1962; Cote and Burn, 2002; Hinkelet al., 2005), block failure as a result of lakeshore steepening (Linet al., 2010; Niuet al., 2011), wave action and thaw slump that expose massive ice to solar radiation (Kokeljet al., 2009; Linet al., 2010), and incorporation of adjacent ponds into the lake (Billings and Peterson, 1980). Under the influence of prevailing summer wind direction (Hinkelet al., 2005), amount of solar insolation received by the lakeshore (Ulrichet al., 2010), sand dunes (Sellmanet al., 1975), snow cover distribution (Payetteet al., 2004) and local topography (Pelletier, 2005), the lateral expansion of thermokarst lakes generally show an oriented pattern in specific areas. In addition, bedrock tectonics and its repercussions in the overlying frozen sediments is believed to be another factor that form oriented lakes (Allenby, 1988; Grosswaldet al., 1999; Lombardo and Veit, 2014). Plafker (1964, 1974) suggested that the lakes are a projection on the surface of subsiding or vibrating basement blocks. Table 1 listed the summarized factors influencing initiation of thermokarst lakes.

Table 1 Factors that initiate thermokarst lakes

2.2 Stages of thermokarst lake development

Due to the complex process of thermokarst lake development (Morgensternet al., 2008), there are numerous stages involved, from its initiation to drainage. Soloviev (1973) identified four stages of thermokarst lake development, they are: (1) the initial stage of ice-wedge thawing within flat polygons; (2) a shallow depression formed with pooling water; (3) mature thermokarst lake formation in the broad basin after complete thawing of the upper permafrost; and (4) lake drainage and a pingo developed in the old lake basin (Kokelj and Jorgenson, 2013). In Yedoma deposits of the Lena Delta region, Morgensternet al. (2011) divided thermokarst lake development into five stages including: (1) flat polygons in undisturbed Yedoma uplands; (2) lateral and vertical thermokarst development, and lake sedimentation and talik not fully developed; (3) lake only with lateral expansion, and full development of lake sedimentation and taliks; (4) partial lake drainage, exposing lake sediments to ice aggradation and peat accumulation; (5) pingo developed in the old lake basin. However, the development stages of thermokarst lakes on the QTP are different from the situation listed above. Based on field investigations and monitoring on a typical thermokarstlake in Beiluhe region of the QTP, Lin (2011) pointed out that thermokarst lake development mainly includes the following four stages: (1) initiation: water gathering in the disturbed area and transport heat to the underlying soils; (2) development: vertical and lateral expansion appeared as the result of permafrost thawing; (3) stabilization: vertical thermokarst stopped, and lakeshore retrogression slowed down; (4) recovery: lake dries and periglacial features begins to develop and new permafrost develops.

3 Temporal evolution of thermokarst lakes

3.1 Shrinkage of thermokarst lakes

Based on geo-rectified aerial photographs and remote sensing imagery, numerous studies have documented changes in thermokarst lake extent in various locations across permafrost regions of the Northern Hemisphere. In this study, we summarized the location of lake change detection studies (Figure 2), and the evolutionary trend and magnitude in each study is listed in table 2. In the Arctic and sub-Arctic regions, thermokarst lakes have been mainly experiencing the process of shrinkage or disappearance (Yoshikawa and Hinzman, 2003; Hinkelet al., 2005; Smithet al., 2005). Kokelj and Jorgenson (2013) summarized that thermokarst lake drainage can be affected by the lake water balance (Pluget al., 2008; Labrecqueet al., 2009; Pohlet al., 2009) or by some external factors, such as forming a drainage pathway resulting from the melting of ice-wedge networks; gully erosion towards a lake; tapping by a river, stream or other lakes, and coastal erosion (Hinkelet al., 2007; Marshet al., 2009; Arpet al., 2011). In the discontinuous permafrost zones, lake water drainage is mainly caused by open talik penetration (Yoshikawa and Hinzman, 2003). Drainage or shrinkage of thermokarst lakes can be extensively found in permafrost regions (Figure 2). Smithet al.(2005) showed that large lakes (>40 ha) have decreased 11% in number and 6% in area from 1973 to 1998 in a 515,000 km2area of Siberia. Marshet al.(2009) found 41 lakes have drained in the Canadian Western Arctic between 1950 and 2000, and the rate of drainage slightly decreased during this time period. Carrollet al.(2011) noted a net reduction of more than 6,700 km2in lake area between 2000 and 2009 across Canada based on the Moderate Resolution Imaging Spectro-radiometer (MODIS) instruments. Morgensternet al.(2011) found that developing thermokarst lakes on yedoma uplands of Lena Delta occupy only 2.2% of the study area compared to 20.0% occupied by thermokarst basins, which indicated an obvious shrinkage of thermokarst lakes in the past decades. In addition, thermokarst pond shrinkage is also widely reported in permafrost regions. For example, Yoshikawa and Hinzman (2003) noted drained and shrunken thermokarst ponds over the last 50-100 years in the discontinuous permafrost zone near Council, Alaska. Riordanet al.(2006) found that the surface water area of closed-basin ponds in sub-arctic Alaska decreased by 31%-34%, and the total number of closed-basin ponds decreased by 54%-55% during the period from 1950 to 2002.

3.2 Increase of thermokarst lakes

There are a few studies that document the increase of thermokarst lakes in permafrost regions (Figure 2). Using high-resolution imagery, Joneset al. (2011) found that the number of water bodies (>0.1 ha) increased by 10.7% from 1950-1951 to 2006-2007 in the northern portion of the Seward Peninsula in Alaska, while the total surface area decreased by 14.9% during the same periods. Linet al. (2011b) found an obvious increase of thermokarst lakes and ponds in the Qinghai-Tibet Engineering Corridor caused by construction and maintenance of the Qinghai-Tibet Highway (QTH). In addition, based on aerial photographs in 1969 and SPOT-5 satellite images in 2010 of a 10-km wide transect along the Qinghai-Tibet Railway (QTR) from the Chumaerhe High Plateau to Beiluhe Basin, thermokarst lakes in the region increased by 867 in number, and 1.7×106m2in area from 1969 to 2010. Although there are no studies about the evolution of thermokarst lakes in large areas of the QTP, low permeability of the mudstone under the lake bottom may prevent the disappearance of thermokarst lakes in this area. Therefore, with the thawing of permafrost caused by climate warming (Jinet al., 2006; Cheng and Wu, 2007) and a gradual precipitation increase (Wuet al., 2005; Geet al., 2008), the number of thermokarst lakes and the area they cover in the QTP may increase in the future.

4 Carbon release from thermokarst lakes

Permafrost soils contain an estimated 1,700 Pg of carbon, nearly twice as much as in the atmosphere (Schuuret al., 2009; Tarnocaiet al., 2009). It is understandable that the release of carbon in the permafrost is a slow and long process, as the thawing and degradation of the permafrost influenced by global warming is a slow and long process. However, thermokarst lakes that are caused by the thawing of ice-rich permafrost and ever-present taliks deep within the permafrost, provides developed channels for carbon release from deep frozen soils and top of the permafrost. In the developing process of a thermokarst lake, the carbon created by anaerobic decomposition of fossils and fresh organic matter previously locked infrozen soils is released, particularly in yedoma (organic-rich, ice-supersaturated Pleistocene-aged loess) dominated permafrost zones (Schirrmeisteret al., 2011), enhancing greenhouse gases (carbon dioxide and methane) production and emission to the atmosphere (Zimovet al., 1997; Phelpset al., 1998; Nakagawaet al., 2002). Zimovet al. (1997) evidenced large amounts of winter methane emission from thermokarst lakes in northern Siberian, which explained why the highest concentration and greatest seasonal amplitude of atmospheric methane occurs in the Northern Hemisphere (Funget al., 1991). Measured results from stable and radiocarbon isotopes show that the methane emitted from these lakes in winter was derived largely from Pleistocene-aged carbon, because most of the northern Siberian plains during the Pleistocene were un-glaciated and accumulated abundant organic carbon in sediments (Zimovet al., 1997). However, the magnitude of these methane emissions remains uncertain because most methane is released through bubbling, which is hard to capture. Walteret al. (2006) reported a new method that using umbrella-shaped floating bubble traps to gather and quantify methane emissions, and the results show that the methane flux from thaw lakes in northern Siberian is much higher than previously estimated (Zimovet al., 1997). Moreover, thermokarst lakes are thought to have formed frequently during the Holocene Thermal Maximum (Cote and Burn, 2002; Walteret al., 2007), which may have largely contributed to the increase of global atmospheric methane concentration during the early Holocene (Walteret al., 2007).

Figure 2 Illustration and site localities of reported thermokarst lake changes in permafrost regions of the Northern Hemisphere.

Table 2 Temporal evolution of some quantitatively reported thermokarst lakes

Soil organic carbon pool stored in permafrost has been identified as a major carbon source in the earth system (Grosseet al., 2012). However, carbon in the peat of drained thermokarst lake basins is rarely considered as a main component of soil organic carbon in permafrost (Joneset al., 2012). Old vegetated drained lakes basins generally maintain relatively high productivity because of the re-establishment of very productive plant species (Zonaet al., 2010), which provide ideal conditions for the accumulation of peat carbon. Such peat carbon accumulation on a regional scale and over long time periods may act as a carbon sink, which likely serves to offset greenhouse gas release from thermokarst lakes and other thermokarst landscapes, and should thereby be incorporated into global carbon budget estimations (Joneset al., 2012). In addition, the application of a two-dimensional landscape-scale model by van Huisstedenet al. (2011) found that lake drainage in Siberia strongly limits lake expansion and further limits methane emissions from thermokarst lakes. Therefore, although methane emissions from thermokarst lakes profoundly affect the global atmospheric environment, the magnitude is less alarming than previously estimated (van Huisstedenet al., 2011).

5 Ecological and engineering influence of thermokarst lakes

5.1 Ecological influence and function of thermokarst lakes

Thermokarst lake development has a large impact on local permafrost environments, notably talik formation and development generally cause a change in ground temperature and heat flow in permafrost layers (Burn, 2002, 2005; Linet al., 2011a). In addition, thermokarst lake development also has a great effect on the chemical, physical and geo-morphological processes in the ground under and around thermokarst lakes (Johnston and Brown, 1964; Lunardini, 1996; Moiseenkoet al., 2006), and the thawing of ice-rich sediments around thermokarst lakes can inversely effect the chemistry of lake water (Bretonet al., 2009; Bouchardet al., 2011). Pokrovskyet al. (2011) studied thermokarst lakes in western Siberia and found that both the culturable heterotrophic bacteria, and trace elements (DOC, Fe, Al, TE) concentrations decreased in thermokarst lakes from its initial stage to drainage.

The permafrost is normally considered as an aquiclude, therefore permafrost degradation might influence regional ground water. Thermokarst lakes which completely thaw the underlain permafrost provide channels which connect surface water with groundwater (Yoshikawa and Hinzman, 2003). When some surface water infiltrates into deep ground water under the permafrost layer, a decline in regional groundwater level will occur, resulting in possible desertification.

Thermokarst lakes can also create various ecological landscapes that provide habitats for fish, migratory birds and other wildlife. Alerstamet al. (2001) pointed out that thermokarst lakes can provide feeding and nesting sites for a great diversity of bird species that migrate annually over long distances. Berkes and Jolly (2001) found that when thermokarst lakes having depths exceeding the maximum thickness of the winter ice cover, it can provide habitats for fi sh and other aquatic organisms. Moreover, thermokarst lakes are also extensively used for human purposes as a crucial freshwater source for local communities, resource exploration and development, and for winter ice road construction (Joneset al., 2009; Kokelj and Jorgenson, 2013).

5.2 Engineering influence of thermokarst lakes

As a heat source, the development of thermokarstlakes often cause a significant change in ground temperature and heat flow of the surrounding permafrost (Burn, 2002, 2005), and thereby impact the stability of nearby engineering foundations (Linet al., 2012). Thermokarst lakes influence engineering facilities in certain ways such as: (1) thermal erosion that results in increasing temperatures and decreasing permafrost strength under or nearby engineering foundations (Johnston and Brown, 1964; Sellmannet al., 1975; Lunardini, 1996), which leads to foundation subsidence or deformation. (2) due to changing thermal exchange between air and ground surface after engineering construction, a thaw sandwich generally forms under the engineering foundation, especially in roadbeds (Liu and Wu, 2000). Such a thaw sandwich under roadbeds generally acts as a pathway for ground water flow (Jinet al., 2008). Therefore, if a thermokarst lake develops near a roadbed, lake water will penetrate into the soil under the roadbed and accelerate its subsidence. (3) the roadbed toe will soften and lose its stability when it sits within the lake water for a long time, leading to problems such as slope cracking (Linet al., 2009, 2012). (4) soil erosion resulting from lakeshore collapse will directly impact engineering foundation stability and its efficient operation.

At present, studies concerning the influence of thermokarst lakes on engineering projects are mainly concentrated in the permafrost region of the QTP, and these studies included the thermal impact of thermokarst lakes on roadbeds of the QTH and the QTR (Linet al., 2009, 2012), oil pipelines (He and Jin, 2010) and tower foundations of the Qinghai-Tibet DC transmission line (Yuet al., 2012). The modeled results of a thermokarst lake in the Beiluhe Basin of QTP (BLH-A lake) shows that whether a thermokarst lake can influence the temperature of permafrost under the roadbed and how about the degree is determined by the annual mean lake-bottom temperature and the horizontal distance from the roadbed to lake-edge (Linet al., 2012). In addition, in order to quantitatively evaluate thermal erosion from thermokarst lakes to roadbeds, Linet al. (2011a) and Niuet al. (2013) calculated the heat transported from BLH-A lake to the adjacent permafrost, and the results show high heat release from the thermokarst lake. Therefore, if a thermokarst lake develops close to the roadbed, such heat will greatly influence roadbed stability.

6 Summery and conclusions

Thermokarst lakes are widely distributed in permafrost regions of the Arctic, sub-Arctic, and Qinghai-Tibet Plateau. Recent literature reveals that methods used for thermokarst lake study mainly include field investigation and monitoring, remote sensing and image interpretation, statistical analyses and numerical simulation, age dating and isotope measurement. The study topics focused on initiating factors and temporal evolution of thermokarst lakes, carbon release from thermokarst lakes and feeding back to climate warming, and ecological and engineering influence of thermokarst lakes.

Climate warming, forest fires, surface water pooling, surface vegetation removal, geotectonic fault and human engineering activities are all influencing factors that initiate thermokarst lakes, through increasing ground temperatures and thawing of ground ice in the permafrost. The development of a thermokarst lake can be identified in 3-5 stages, from initiation to local permafrost recovery. In the Arctic and sub-Arctic regions, thermokarst lakes have been mainly experiencing the process of shrinkage or disappearance, while an obvious increase of thermokarst lakes and ponds in the Qinghai-Tibet Engineering Corridor has been recognized based on aerial photographs and SPOT-5 satellite images.

An estimated carbon volume of 1,700 Pg, locked within the frozen soil, can be released by anaerobic decomposition of fossils and fresh organic matter during the developing process of thermokarst lakes, thus proving a feed back to climate warming. The channels provided by thermokarst lakes which completely thaw the underlain permafrost serve as connections between the surface water and groundwater. When some surface water infiltrates into deep ground water under the permafrost layer, a regional groundwater level decline will occur, resulting in possible desertification. Also, local infrastructures can also be influenced by thermal erosion, softening of the subgrade soils and soil erosion, if a thermokarst lake is nearby.

Based on a comprehensive review of literature on thermokarst lakes, it is suggested that studies on thermokarst lakes need to consider the balances among water, ground ice, sediment, and energy exchange, along with the current study topics.

Acknowledgments:

We acknowledge support from the State Key Development Program of Basic Research of China (973 Plan, 2012CB026101), the Western Project Program of the Chinese Academy of Sciences (KZCX2-XB3-19), the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 41121061), and the National Sci-Tech Support Plan (2014BAG05B05).

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10.3724/SP.J.1226.2014.00388.

Received: April 16, 2014 Accepted: June 20, 2014

*Correspondence to: Dr. FuJun Niu, Professor of Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences. No. 320, West Donggang Road, Lanzhou, Gansu 730000, China. Tel: +86-931-4967263; E-mail: niufujun@lzb.ac.cn