Created: 2014-01-28 16:09:28
Modified: 2014-01-28 16:14:12
Active layer monitoring at the Nadym CALM grid was initiated in 1997. Since 1972 annual thaw depth monitoring was conducted at several transects and 10х10 m plots characteristic of dominant landscapes of the Nadum region and adjacent to the CALM grid. The Nadym site is located in the northern taiga with sporadic permafrost on the III fluvial-lacustrine plain with elevation ranging from 25 to 30 m above sea level. The plain is composed of sandy deposits interbedded with clays, occasional covering of peat. Patches of permafrost are closely associated with peatlands, tundras, bogs and frost mounds. In the central part of the III fluvial-lacustrine plain flat peatlands with cloudberry-shrub-lichen-moss cover are dominate Sedge-moss mires and hummocky sedge-shrub moss-lichen tundras are subdominant nature complexes. From nature complexes flat peatland is dominant, bog and tundra are subdominants. Peatland area characterized by Ledum palustre, Rubus chamaemorus, Sphagnum fuscum and Cladina stellaris; hummocky tundra is characterized by Betula nana, Ledum palustre, Cladina stellaris, Cladina rangiferina and Sphagnum Lindbergii in pools, bog is characterized by Carex rotundata, Carex limosa, Eriophorum russeollum, Shagnum Lindbergii and Betula nana, Eriophorum vaginatum on rare hummocks. The measurements of the active layer thickness show that the smallest values of seasonal thaw depths are observed under Rubus chamaemorus-Ledum palustre-Sphagnum-Cladina rangiferina cover on flat peatland. This type of peatland serves as an indicator of seasonal thaw depth. Areas with deepest thaw are developed in large sedge-moss pools within peatlands and in bogs. Rubus chamaemorus is developed at grid points with minimal thaw depth, but Sphagnum lindbergii is characteristic for places with maximal thaw depth. The interannual node variability of thaw depths at this grid averaged 20 %. The minimum values of this parameter are characteristic for the flat peatland, the maximum values are fixed on hummocky tundra. The same was observed on plots and transects on which measurements were carried out since 1972. For 1997-2007 period the maximal thaw depth is fixed in 2002 with warm summer and very high summer precipitations. In this year average thaw depth was 143 cm. The minimal thaw depth is observed in 1999 cold year. The least thaw depths are observed on a flat surface of a peatland where average depth is 80сm. Sites with deeper thaw depth are characteristic for the downturn places occupied by shrub-sedge-peat moss bog with thaw depth - 151сm. Sites with deep thaw depth are measured also on hummocky tundras with peat hummocks, frost boils and pools where thaw depth is 152сm.The greatest values of volumetric moisture are observed on a peatland and a bog. On the average for CALМ grid the value of volumetric moisture makes 67 %. The least values of moisture (20 %) are characteristic for hummocks, the greatest (89 %) - for pools of hummocky tundra and a peatland of CALМ grid. The steady increase in thaw depth in all natural complexes is observed. It corresponds to the air temperature steady increase from the beginning of 1970th.
SAMPLING DESIGN AND METHOD:
1-ha grid consists of a square array of permanent stakes separated by 10 m, yielding an 11 × 11 array of sampling nodes on each grid. Thaw depth sampling was conducted at least twice by manual probing at each stake. The two (or more) values for each sampling point are averaged, yielding a maximum of 121 data points per grid per probing date.
CALM Russia Earth Cryosphere Institute SB RAS
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