Arctic Borderlands Ecological Knowledge Co-op
Indicator Assessment: Permafrost and Soil Temperatures
Soil temperatures and the distribution of permafrost are good candidates as indicators of climate change. Researchers have spent much effort examining the active layer. As its name implies this is the layer of soil that goes through a period of freezing and thawing each year; it is the contact zone between permanently frozen soil (permafrost) and the atmosphere.
There are two different approaches to monitoring. One can carry out physical probing of the active layer or take instrument measurements of soil temperatures. Nelson et al. (1996) compare the relative merits of these methods:
Physical probing: use of a small diameter metal rod to probe the bottom of the active layer (i.e. pushing a rod down to the depth of "refusal" and then measuring the depth).
Soil Temperatures: use of temperature probes to collect detailed information on soil temperatures at specified depths. Mackay (1995) used a steel tube that contained a series of temperature probes to probe the ground and identify the 0 Centigrade level and was able to combine this with a survey of the active layer. Other researchers have set up permanent temperature probes inserted in the ground and then taken temperature readings periodically or continuously by hooking the temperature thermistors up to a datalogger.
Existing Data Sets
The active layer protocol laid out by the International Tundra Experiment (ITEX) suggests a two level measurement program which combines both permanently installed soil temperature probes using data loggers as well as physical probing of the active layer (Nelson et al. 1996). The protocol recommended for physical probing relies on a sampling design proposed by the International Permafrost Association for the Circumarctic Active Layer Monitoring program (CALM).
The sampling approach is known as a systematic stratified unaligned sampling scheme and, despite the name, is straightforward. A large grid (100m x100m) is laid out and subdivided into 100 squares (each 10m x10m). This reference grid is then used to identify 100 sampling locations where probe measurements are taken (Nelson et al. 1996, Appendix 6). The authors recommend that the location of the probe measurements should be permanently marked with stakes - this would allow observers in later years to replicate measurements. The active layer should be measured at least once at the end of the summer when the bottom of the active layer can be discerned. Long term data sets (i.e. 10 years or more) are useful in distinguishing between local variation and long term trends.
There is an opportunity for community participation in selecting a site suitable for measuring the active layer, as well as carrying out the field measurements. It would be helpful to have a specialist visit the community to help set up the grid and sampling protocol in the first season. After that data collection could be directed by the community.
Mackay, J. Ross 1995. Active layer changes (1968-1993) following the forest-tundra fire near Inuvik, N.W.T., Canada. Arctic and Alpine Research 27:323-336.
Nelson, F., J. Brown, T. Lewkowicz and A. Taylor 1996. Active Layer Protocol. In: ITEX Manual 2nd Ed., Ulf Molau and Per Molgaard (eds), Danish Polar Center.
Written by S. Gilbert, March 1997.