Location: Northwest Watershed Research CenterTitle: Sensible heat balance estimates of transient soil ice contents for freezing and thawing conditions
|KOJIMA, YUKI - Iowa State University|
|HEITMAN, JOSHUA - North Carolina State University|
|REN, TUSHENG - China Agricultural University|
|HORTON, ROBERT - Iowa State University|
Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2016
Publication Date: 5/13/2016
Citation: Kojima, Y., Heitman, J., Flerchinger, G.N., Ren, T., Horton, R. 2016. Sensible heat balance estimates of transient soil ice contents for freezing and thawing conditions. Vadose Zone Journal. 15(5):11.
Interpretive Summary: Ice content of frozen soils has a large influence on water movement, infiltration, and ultimately runoff and flooding, but there are no easy and accurate methods to measure soil ice content. A new heated probe sensor to measure soil ice content was laboratory-tested. The sensor was able to determine ice content changes during initial freezing and final thawing, but was not accurate during extended frozen periods when used as designed. However, by using measurements from the probe to estimate changes in the soil's heat capacity, soil ice contents could be estimated well. The results are promising for providing a new soil sensor to measure soil ice content that can be used for predicting the likelihood of flooding and other adverse effects associated with soil freezing.
Technical Abstract: Soil ice content is an important component for winter soil hydrology. The sensible heat balance (SHB) method using measurements from heat pulse probes (HPP) is a possible way to determine transient soil ice content. In a previous study, in situ soil ice contents estimates with the SHB method were inaccurate, due to thermal conductivity errors and the use of relatively long time steps for calculations. The objective of this study is to examine the SHB method for ice content determination with relatively simple soil freezing and thawing event by using shorter time steps for calculations. A soil freezing and thawing experiment was performed with soil columns and heat exchangers. Transient soil ice contents in the soil columns during soil freezing and thawing were determined with the SHB method. The SHB method was able to determine dynamic changes in soil ice contents during initial freezing and final thawing for soil temperatures between -5°C and 0°C when latent heat values associated with ice formation or with thawing were relatively large. During an extended freezing period, when soil temperatures were below -5°C, the small associated latent heat fluxes were below the sensitivity of the SHB method, and the SHB method did not provide accurate estimates of ice contents with time. However, the soil ice contents during the extended freezing period could be estimated well from changes in volumetric heat capacity (C) determined with HPP. Thus, combining the SHB method for initial freezing and final thawing, with a change in C method for extended freezing periods, allowed determination of dynamic soil ice contents for the entire range of freezing and thawing events. HPPs can be used to measure soil ice contents.