THE EFFECT OF DEGASSING METHOD OF FROZEN SOILS ON THE TEST RESULTS OF METHANE CONCENTRATION

Abstract

The gas composition of frozen soils has not been sufficiently studied, although in recent years this question has been repeatedly raised in the context of the correlation between global climate changes and permafrost, paleoreconstructions of the conditions of past geological epochs and problems in developing of frozen territories. A significant role is played by methane with very wide range of concentrations that depends on the composition, properties and genesis of soils. The accuracy of degassing process of frozen samples is crucial for the study of the gas component of frozen soils because of possible mixing with atmospheric air, the composition of the gas can be significantly distorted. Another problem is the variability of the gas composition in frozen samples caused by the heterogeneity of biogeochemical processes and the migration of gases during freezing. The article focuses on the comparison of the two most widely used field methods of degassing of frozen soils from the point of studying methane as one of the most researched greenhouse gases — the headspace method and the large sample one. The gas was collected by the headspace method from three randomly selected parts of 36 monoliths, after which the entire remaining monoliths were degassed by the large sample method. The possible inaccuracies and difficulties arising with different ways of degassing the samples were estimated. The methane concentration values obtained by different degassing methods of samples of frozen soils were compared. The values obtained by both methods for methane concentrations less than 100 µl/kg were comparable. A wide dispersion of values was observed at high concentrations: the mean values measured by different methods differed up to 20 times. The headspace method shows on average, values above the large sample method. Most likely, this excess is also associated with a large heterogeneity of methane distribution in the frozen soils, as a result of which the headspace method can give higher values.