盐分对季节性冻融土壤蒸发的影响试验及数值模拟研究

【目的】探究盐分对季节性冻融土壤蒸发的影响规律。【方法】在内蒙古河套灌区开展了B1和B2二组不同含盐量下(B1:7.80 g/kg;B2:41.16 g/kg)的野外土柱蒸发试验,建立了考虑盐分影响(该影响由盐分阻抗和土壤表面阻抗体现)的冻融土壤蒸发数值模拟模型。采用土柱试验结果对模型进行了率定验证,并与SHAW模型进行了对比分析。在此基础上,应用该模型对9种不同含盐量(S1—S9:0、2.5、5、7.5、10、15、20、35、50 g/kg)下的冻融土壤蒸发进行了模拟。【结果】土壤含盐量不同导致的土壤蒸发强度差异显著,特别是在土壤冻结初期和融通期,土壤含盐量较低的B1土柱蒸发强度分别约是B2土柱的1.5倍和1.8倍;与SHAW模型相比,考虑盐分影响的冻融土壤蒸发模型能准确反映受盐分影响的冻融土壤蒸发过程,更适用于受盐渍化影响的季节性冻土区;冻融土壤蒸发量随含盐量增加呈现出先增后减的变化趋势,在含盐量为S6时,土壤蒸发量最大,为136.3 mm;相比无盐土S1,S2—S6的土壤蒸发分别增加了1.09%、13.68%、56.22%、73.73%和86.46%,而对比S6,S7—S9的土壤蒸发分别减少了10.20%、26.34%和42.55%。【结论】盐分对季节性冻融土壤蒸发影响显著,其作用为先促进后抑制,考虑盐分影响的冻融土壤蒸发模型可以提升盐渍农田蒸发的模拟精度。

Effects of Salt Content on Evaporation from Seasonally Frozen Soil:Experimental Measurement and Numerical Simulations

【Background】Seasonally frozen soils are a widely distributed land resource in China,and sustaining their agricultural production is essential to meet the increased demand of the growing population for foods.Hetao irrigation district in Inner Mongolia is one of three major irrigation districts located in seasonally frozen regions,and its agricultural production is constrained by soil salinization and water shortage.As soil salinity and soil evaporation are interconnected,understanding the changes in evaporation from soils with different salinity is important for improving water and salinity management in seasonally frozen soils.【Objective】The purpose of this paper is to evaluate the impact of salt content on evaporation from soils subject to freezing-thawing cycles.【Method】Soil columns packed by soil with salt content 7.80 g/kg(B1)and 41.16 g/kg(B2),respectively,were used in the experiments conducted in Inner Mongolia.Evaporation from the columns under a thawing-freezing process was measured,from which a numerical model,considering the effects of salt contents on soil surface impedance,was developed to calculate the evaporation.We calibrated and validated the model against the experimental data and compared it with the SHAW model first,and then used it to simulate evaporation under freezing-thawing processes from soils with salt contents ranging from 0 to 50g/kg.【Result】The impact of salt content on evaporation was noticeable,especially at the beginning of the freezing and thawing processes,with their associated average evaporation from the B1 treatment being1.5 times and 1.8 times that of the B2 treatment,respectively.Compared with the SHAW model,the numerical model simulated the evaporation process reasonably well and was more suitable for seasonally frozen soil with salinization.During the freezing-thawing process,the evaporation from soil increased first followed by a decline as the salt content increased.When the salt content was 15 g/kg,the maximum evaporation was 136.3 mm.Compared to soil without salinization,increasing salt content from 2.5 g/kg to 20 g/kg increased soil evaporation from 1.09%to 86.46%.In contrast,increasing salt content from 20 g/kg to 50 g/kg reduced the evaporation gradually by up to 42.55%【.Conclusion】Salt content has a great impact on evaporation from seasonally freezing-thawing saline soil.With salt content increasing,the evaporation increased first followed by a decline.The proposed numerical model considering the effects of salt improved accuracy of the predicted evaporation.Our results have implications for improving our understanding of the mechanisms underlying evaporation from seasonally frozen salt-affected soils and provide methods for simulating soil and water dynamics in these regions.