Thermokarst lake to terrestrial ecosystem

Feedback mechanisms

  • Atmospheric temperatures (regional, well-established): Changing air temperatures in this system are causing later freeze-up and earlier break-up of Arctic rivers and lakes (Magnuson et al., 2000, 1743) and mirror arctic-wide and even global increases in air temperatures (Chapman and Walsh, 1993, as updated by Serreze et al. 2000, n.p). Initial permafrost warming leads to development of thermokarst and lake expansion, followed by lake drainage as the permafrost degrades further (Smith et al. 2005,1425).
  • Soil Temperatures (local, well-established): Longer and warmer seasons, an advancing tree line and increased abundance of shrubs lead to warmer soil temperatures (Hinzman et al. 2005, 255). Increased soil temperatures especially promote continuous permafrost thawing and can prevent permafrost reformation in winter months. The spatial pattern of lake disappearance strongly suggests that the thawing of permafrost is driving the observed losses (Smith et al. 2005, 1425).
  • Albedo (local, well-established): Small puddles or ponds that are formed from permafrost melting accelerate subsurface thaw through lower albedo and additional heat advected into the pond through runoff (Hinzman et al. 2005, 15). The increased advected heat flowing into the pond may overtime can cause increased lake formation by causing more permafrost to melt. Increased vegetation, lower precipitation (snowfall) levels, larger lake area and melting ice surfaces from shorter and warmer winter seasons in high latitudes may act as a positive feedback to radiative forcing and in turn enhance atmospheric warming (Hinzman et al. 2005, 272).
  • Precipitation/snowfall (local, well-established): Analysis reveals widespread decline in lake abundance and area despite slight overall increases in precipitation (Smith et al. 2005,1429). Increased precipitation in the form of snowfall may have either an insulating or cooling affect on soil temperatures depending on several variables such a timing, duration, accumulation, and melting processes of seasonal snow cover, density, structure, and thickness of seasonal snow cover etc. (Zhang. 2005, 1).

Specific lake dominated ecosystem feedback mechanisms

  • Active layer (local, well-established): Active layer is the layer of unfrozen soil through which free water can move.Shallow water tables and extensive, low-permeability peatlands ensure continued survival of many lakes, even where permafrost is absent (Smith et al. 2004, 303). Net increases in lake abundance and area have occurred in continuous permafrost, suggesting an initial but transitory increase in surface ponding (Smith et al. 2005,1429).
  • Active layer (local, well-established): Depending upon the local surface energy balance, the thawed ground may refreeze or the permafrost can continue to degrade (Hinzman et al. 2005, 265). Numerous studies have demonstrated that lowering the water table can markedly increase CO2 emission rates from soil (Moore et al.1998, 386). In certain soil conditions and once the soil has reached a specific saturation point, CO2 production declines and CH4 production increases largely because CO2 production is an aerobic process and CH4 production is an anaerobic process (Oechel and Vourlitis, 1997 n.p.). CH4 is a much more potent and volatile gas than CO2, which may lead to more dramatically atmospheric temperatures.

Specific terrestrial ecosystem feedback mechanisms

  • TKL drainage (local, well-established): Thermokarst lakes and ponds may begin to fill or drain depending upon the direction of the hydraulic gradient beneath the lake (Hinzman et al. 2005, 65). Thermokarst lakes are prone to either spatial increase due to thermokarst processes, or complete drainage in less than one day due to melting of channels through ice-rich permafrost (Marsh et al. 2009, 145). As Clarke (1982) demonstrated through a combination of observations and application of a modified glacier outburst flood model (2001), it is suggested that rapid drainage in less than a day could be explained by the melting of ice-rich permafrost by the thermal energy of the lake water (Marsh et al. 2009,146).


Shift from lake ecosystem to terrestrial ecosystem

Important shocks that contribute to the regime shift include:

  1. Rapid lake drainage (local): rapid lake drainage occurs when the lake water melts the permafrost and creates outlet channels through the permafrost. Rapid drainage can occur within a day (Marsh et al. 2009, 146).

The main external direct drivers that contribute to the shift include:

  • Climate change (global, well-established): Rising air temperature leads to increased soil temperatures, which in turn lead to deeper active layers and permafrost degradation. As the permafrost thaws, CO2 and CH4 are emitted, further increasing climate change (Hinzman 2005, 260; Karlsson et al. 2011, n.p.). However, there is a delay in this feedback mechanism, and the effects of this local and regional process is global, causing the temperature to rise even further. Since climate change has a significant effect on temperature in the Arctic regions, we expect shifts in ecosystems to increase over time.

Slow internal system changes that contribute to the regime shift include:

  • Permafrost thawing (regional; well-established): As a result of warmer temperature and longer thawing periods, the active layer deepens, warming the permafrost (Karlsson et al. 2011, 2; Hinzman 2005, 262). Up to a certain point, thawing permafrost initially increases the development of thermokarst lakes. But as permafrost degradation continues it causes water to drain deeper and eventually the lakes become permanently drained (Marsh et al. 2009, 148).
  • Thermokarst lake drainage (local to regional; well-established): Since the temperature of water is higher than ice, lake drainage melts the permafrost even further, causing a reinforcing feedback. If the permafrost layer is penetrated, this often leads to permanent drainage (Marsh et al. 2009, 148,157).

Shift from terrestrial ecosystem to lake ecosystem

The main external direct drivers that contribute to the shift include:

  • Climate change (global): Climate change causes the temperature to rise, which melts the soil on which forests develop, changing the physical foundation of the forests (Hinzman 2005, 262).

Slow internal system changes that contribute to the regime shift include:

  • Thawing (regional): As ice-rich soils (and underlying permafrost) thaw it changes the conditions for the forest growing on top of it. When the roots of the trees get flooded, the trees die and ponds and lakes replaces the forest (Hinzman 2005, 262).


Summary of Drivers

# Driver (Name) Type (Direct, Indirect, Internal, Shock) Scale (local, regional, global) Uncertainty (speculative, proposed, well-established)
1 Rapid lake drainage Shock Local Proposed
2 Climate change Direct Global Well-established
3 Permafrost thawing Internal Regional to local Well-established
4 Themokarst lake drainage Internal Local Well-established

Key thresholds

Shift from lake ecosystem to terrestrial ecosystem

Air temperature: no exact tipping point, dependent on specific locality. Rising air temperature pushes regime 1 to a threshold which eventually shifts into regime 2 as permafrost degrades further allowing lakes to drain.

Soil temperature: no exact tipping point, dependent on specific locality. Rising soil temperature pushes regime 1 to a threshold which eventually shifts into regime 2 as permafrost degrades further, allowing lakes to drain.

Hydraulic processes:

  1. State of the permafrost: no exact tipping point, dependent on specific locality. As permafrost shifts from the continuous to the sporadic type and decreases in thickness, water will breach through allowing lakes to drain (Hinzman et al. 2005, 263).
  2. State of the active layer: no exact tipping point, dependent on specific locality. As thickness of the active layer increases ground water flow (Marsh et al. 2009, 156).
  3. Soil moisture: no exact tipping point, dependent on specific locality. More moist soil increases ground water flow, allowing lake drainage (Marsh et al. 2009, 156).

Shift from terrestrial ecosystem to lake ecosystem

There is little knowledge on the thresholds that determine if terrestrial ecosystems will shift into lake ecosystems yet all collected evidence suggests that that shift is unlikely to occur due to the dominating feedbacks that are reinforcing the terrestrial state. Therefore we did not analyze the thresholds from regime 2 into regime 1. 

Leverage points

  • Atmospheric temperatures (regional/global, speculated): Even though areas of drained lakes could be encouraged to develop vegetation, this vegetation will still not compensate for the extensive CO2 and CH4 emissions from permafrost thawing and the thermokarst lake drainage processes (Schaefer et al. 2012,18). Furthermore, even if we are able to drastically reduce emissions on a global scale, the significant delay in feedbacks linking back to climate change will remain making management difficult. In addition, the feedbacks from CO2 and CH4 emissions from thawing permafrost, accelerating permafrost degradation, will not be reversible on human time scales (Schaefer et al. 2012,18).

Summary of Ecosystem Service impacts on different User Groups

References (if available)
Provisioning Services
Freshwater -
Vincent et al. 2013 - Hinzman et al. 2005
Food Crops ?
Feed, Fuel and Fibre Crops ?
Livestock ?
Fisheries -
- Vincent et al. 2012 - Vincent et al. 2013
Wild Food & Products 0
Timber +
Hassol et al. 2004
Woodfuel +
Hassol et al. 2004
Hydropower -
Vincent et al. 2013
Regulating Services
Air Quality Regulation ?
Climate Regulation -
Vincent et al. 2013
Water Purification ?
Soil Erosion Regulation -
Witthaus et al. n.d.
Pest & Disease Regulation ?
Pollination ?
Protection against Natural Hazards ?
Cultural Services
Recreation -
Aesthetic Values ?
Cognitive & Educational -
Vincent et al. 2013
Spiritual & Inspirational -
Vincent et al. 2013

Uncertainties and unresolved issues

There is still little knowledge surrounding the thresholds that determine if a terrestrial ecosystem will shift into a lake ecosystem. “The increased pressure that polar systems are experiencing implies that we are approaching critical thresholds (such as the thawing of permafrost and vegetation change), although the nature and timing of these thresholds are regionally variable and uncertain” (Hassan et al. 2005, 736).

Increased variability of environmental conditions e.g. change in snow depth and frequency makes it difficult to anticipate future conditions and results in greater uncertainty and risk for decision makers (Hinzman 2005, 284). Increased winter flow rates could have a wide range of impacts, including changes in stream chemistry and aquatic habitat, increased stream and river icing, and other uncertain implications on erosion and sediment flux (Hinzman 2005, 264).

The potential changes in northern wetlands and lake extent as a result of increased evaporation and potential drainage are a major source of uncertainty for models of methane release from Arctic permafrost (Vincent et al. 2013, 30).