Impact of organic matter content on loess thermo-physical properties

ABSTRACT WITHDRAWN



Contact First Author: Michel Sliger; mich.slei@gmail.com

Previously Published Material: Part of it was presented at a national professional workshop last spring. Sliger, M. and Fortier, D. (2014) Beaver Creek soils: From genesis to physical properties. 5th Annual Workshop of the Canadian Permafrost Network of Expertise, June 4-7, Dawson City, YT, Canada.

Abstract ID#: 35789

 

English Abstract:
Subsurface water has been recognized as a key component of permafrost and ecological dynamics. Based on the peat’s water-retention capacity, we hypothesized that the organic matter (OM) content of soils plays a significant role in heat and mass transfers. We mapped the distribution of OM in the active layer of permafrost at the landscape scale and retrieved 100 active layer and permafrost table samples along a toposequence. Grain size distribution, OM content, porosity, apparent and specific densities, thermal and hydraulic conductivities, heat capacity and unfrozen water content below 0°C were measured in the laboratory and Peclet number were calculated. We developed a dataset of the thermo-physical properties of active layer soils and explored the relationships between OM-influenced active layer properties of different terrain units forming the geosystem and their incidence on subsurface water flow and heat transfers.

The study site (Beaver Creek, Yukon, Canada) was not glaciated during the last glacial maximum and was covered by a thick blanket of ice-rich eolian silt (yedoma deposit), which is typical of unglaciated areas of Yukon, Alaska and Russia (e.g. Beringia). The grain size distribution of the silt was quite uniform and typical of loess deposit. However, the OM content varied markedly (2 to 98%) depending on location in the landscape, it averaged around 17% on topographic highs and around 32% in topographic lows.

OM inclusion strongly influences eolian silt’s properties. It tends to 1) decrease its specific and apparent densities, 2) increase its porosity and water retention capacity, 3) decrease its thermal conductivity, 4) increase its hydraulic conductivity and Peclet number, 5) increase its unfrozen water content for a given temperature below 0°C and 6) increase its specific heat. These results indicate that organic matter content should be taken into account to better model subsurface heat and mass transfers at the landscape scale.

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