Diurnal amplitude of peat soil temperature

The results of monitoring of peat soil temperature in an oligotrophic pine-shrub-sphagnum community at the field station "Vasyugan" in Bakchar district of Tomsk Region are given. Monitoring of soil temperature at depths of 2, 5, 10, 15, 25, 40, 60 and 80 cm was carried out by autonomous temperature logger from June 28, 2005 to September 6, 2010 with a time step of 15 minutes in summer and 1 hour in winter. The results of observation reflect the general patterns of input and output of solar radiation coming onto the active surface. In the warm season diurnal fluctuations of temperature penetrate to a depth of 25 cm. The amplitude of the diurnal temperature variation is 5.9- 10.2 ° C at the surface layer, and 0.3-0.5 ° C at a depth of 25 cm. The diurnal variation of soil surface temperature is usually characterized by a maximum in the middle of the day and a minimum just before sunrise. The maximum soil temperature at a depth of 2 cm is observed at about 4 pm local time in May-June, and at a depth of 5 cm the maximum is observed at 5 pm, at a depth of 10 cm - at 6 pm, at a depth of 15 cm - at 8 pm. At a depth of 25 cm from the surface the maximum temperature is weak, and it is 5 hours later than at a depth of 2 cm. In June and July the minimum soil temperature in the diurnal course at a depth of 2 cm is observed at 6 am. At a depth of 5 cm the time lag is 40 min, at a depth of 10 cm - 1 hour and 30 minutes, at a depth of 15 cm - 2 h 30 min, and at a depth of 25 cm - more than 5 hours. Thermal fluctuations in peat soil are effectively neutralised: in the upper layer due to the high insulating ability of moss, in the lower layers because of the saturation of peat by water and the absence of convective motions. Variations of temperature fluctuations amplitude with a known period allow us to determine the coefficient of effective diffusivity. The effective thermal diffusivity of the upper layer of moss is 8 - 9 cm /hr from June to September. Low values of thermal diffusivity (5.05 cm /hr) are observed in May due to low humidity of mosses.

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