Transformation between Phreatic Water and Soil Water during Freeze–Thaw Periods

Junfeng Chen,Chunyan Miao,Ping Liu,Xiuqing Zheng,Yongxin Xu,Qi Du,Xuguang Gao

doi:10.3390/w10040376

Junfeng Chen, Chunyan Miao + Show 5 more

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https://doi.org/10.3390/w10040376

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Abstract

During freeze–thaw periods, the exchange between shallow groundwater and soil water is unusually strong and bidirectional, which causes soil salinization and affects the accuracy of water resources assessment. The objectives of this study were to explore the laws of transformation between phreatic water and soil water through nine different groundwater table depths (GTDs) and three kinds of lithologies during three successive freeze–thaw periods using field lysimeters. The results showed that phreatic evaporation increased with smaller average soil particle sizes. The differences between phreatic evaporation and recharge to groundwater (DPR) and GTDs were well fitted by the semi-logarithmic model, and the regression coefficients A and B of the model were well fitted by the linear relationship with the average soil particle size. With the increase of soil particle size, the change of DPR decreased with the change rate of soil particle size. The extent of transformation between phreatic water and soil water decreased with the increase of soil particle size. During the whole freeze–thaw period, the negative value of DPR increased with an decrease in GTD. The groundwater depths of zero DPR (D-zero) of sandy loam, fine sand and sandy soil during the freeze–thaw periods were 2.79 m, 2.21 m and 2.12 m, respectively. This research is significant for the prevention of soil salinization disasters and the accurate assessment of water resources.

Highlights

The frozen layer developed downward rapidly from early December to late January, and the phreatic evaporation caused by the rapid freezing of soil profile moisture was relatively large, which was obviously affected by soil freezing when the groundwater table depths (GTDs) was 0.5 m
The transformation between phreatic water and soil water was affected by the lithology, GTD, and the effect of soil freezing and thawing during freeze–thaw periods
From early December to late January, the frozen layer developed downward rapidly, and the phreatic evaporation caused by the rapid freezing of soil profile moisture was relatively large, which was obviously affected by soil freezing when the GTD was 0.5 m

Summary

Introduction

China is the third largest location of frozen soil in the world with a distribution area of permafrost and seasonal frozen soil that account for 22.3% and 53.5% of the total national land area, respectively, and the freeze–thaw periods of the inland basin in north-west China account for nearly half a year.During freeze–thaw periods, the exchange between shallow groundwater and soil water is unusually strong and bidirectional, which is the soil moisture’s upward migration from shallow groundwater caused by soil freezing, and is known as phreatic evaporation to the unsaturated zone during freezing periods; and the downward infiltration recharge of thawed soil water from the frozen layer to groundwater is known as the recharge of thawed water during thawing periods.That is, soil water downward recharge to groundwater and phreatic evaporation appear alternately.The strong exchange between shallow groundwater and soil water is one of the main causes of soilWater 2018, 10, 376; doi:10.3390/w10040376 www.mdpi.com/journal/waterWater 2018, 10, 376 salinization [1,2,3], and affects the accuracy of water resources assessment [4]. Soil water downward recharge to groundwater and phreatic evaporation appear alternately. The strong exchange between shallow groundwater and soil water is one of the main causes of soil. It is important to study the transformation between phreatic water and soil water during freeze–thaw periods for the protection of water resources in shallow groundwater, the prevention of soil salinization disasters, and the accurate assessment of water resources. Investigators have conducted a great deal of research on the mechanisms and laws of phreatic evaporation in non-freezing periods using aspects of the calculation method [5,6,7,8], model [9,10,11,12], and influencing factors [13,14,15,16,17,18]. The research on groundwater recharge has made new progress [25,26,27,28,29]

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