土体冻结过程中不同位置液态水的能量差引起了水分迁移与重分布,进而引发冻胀,关于势能差驱动下的冻土水分迁移问题一直由于技术手段的匮乏而没有完全解决。利用新近推出的可用于冻土水热研究的p F meter基质势传感器与5TM水分传感器,...土体冻结过程中不同位置液态水的能量差引起了水分迁移与重分布,进而引发冻胀,关于势能差驱动下的冻土水分迁移问题一直由于技术手段的匮乏而没有完全解决。利用新近推出的可用于冻土水热研究的p F meter基质势传感器与5TM水分传感器,实时监测研究饱和青藏红黏土单向冻结过程中基质势-液态含水率-温度-含冰量-水分迁移量-冻胀变形之间在时间、空间上的耦合变化关系。结果表明:土体温度场变化引起内部液态水相变,打破了原有的能量平衡,试验结束后12~14 cm土样高处含水率最高达到55%,靠近冻融交界面处(10 cm)的未冻区含水率减小至25.8%,水分整体向冷端发生迁移;土体冻胀的快慢及冻胀量大小与水分迁移速率及数量具有线性关系;试验后土体内总含水率的分布与分凝冰透镜体的分布一致,已冻区液态含水率的分布与温度梯度近似成线性关系,未冻区液态含水率的分布与水分的迁移量有关,与温度梯度无关。此外,温度场对水分场的变化具有诱导作用但二者并不同步,当冻结速率减小到一定程度时水分才开始迁移,第10小时后温度场趋于稳定而水分迁移并未停止。研究成果揭示了土体单向冻结过程中液态水、基质势、温度等物理参数的动态变化过程及内在联系,为冻胀机制的研究以及冻胀模型的建立提供了试验基础。展开更多
土壤水分特征曲线模型作为实验测定土壤水分特征数据的一种替代方法,因其具有计算方便快捷和便于嵌入数值模拟程序的优点,开始受到越来越广泛的关注。虽然文献中存在众多的土壤水分特征曲线模型,但是这些模型的适用范围及拟合性能尚不...土壤水分特征曲线模型作为实验测定土壤水分特征数据的一种替代方法,因其具有计算方便快捷和便于嵌入数值模拟程序的优点,开始受到越来越广泛的关注。虽然文献中存在众多的土壤水分特征曲线模型,但是这些模型的适用范围及拟合性能尚不明确。为了获得更加准确适用的土壤水分特征曲线,在实际应用中通常需要花费大量时间和精力去测试各种模型。为了解决上述问题,在国内外研究成果的基础上收集整理了12种典型的土壤水分特征曲线模型,并利用包含不同质地、有机质含量及容重的8种土壤的实测土壤水分特征数据来评估比较这些模型的模拟性能。模型性能通过均方根误差(RMSE)、平均偏差(AD)、AIC准则(Akaike Information Criterion)和纳什效率系数(NSE)4个指标评估。研究结果表明:大部分的模型能够提供比较接近于实际的拟合结果,评价指标值也比较相近。其中,KCGS2006(包含3个参数)和K1999模型(包含2个参数)拟合效果最好,而Gregson1987(包含1个参数)的拟合效果最差。该研究可以深入了解各种土壤水分特征曲线模型的适用性与局限性,更好地为生态环境建设和农业可持续发展研究中土壤水力参数的选取提供依据和参考。展开更多
Soil water sensors are commonly used to monitor water content and matric potential in order to study hydrological processes such as evaporation. Finding a proper sensor is sometimes difficult, especially for measureme...Soil water sensors are commonly used to monitor water content and matric potential in order to study hydrological processes such as evaporation. Finding a proper sensor is sometimes difficult, especially for measurements in topsoil, where changes of temperature and soil water dynamics occur generally with greater intensity compared to deeper soil layers. We assessed the perfor-mance of Hydra Probe water content sensors and MPS-1 matric potential sensors in topsoil in the laboratory and in the field. A common soil-specific calibration function was determined for the Hydra Probes. Measurement accuracy and sensor-to-sensor variation were within the manufacturer specification of ±0.03 m3·m-3. Hydra Probes can operate from dry to saturated conditions. Sensor-specific calibrations from a previous study were used to reduce sensor-to-sensor variation of MPS-1. Measurement accuracy can be expressed by a mean relative error of 10%. According to the manufacturer, the application range of matric potential readings is from -10 kPa to -500 kPa. MPS-1 delivered also values beyond this range, but they were not reliable. Sensor electronics of the MPS-1 were sensitive to ambient temperature changes. Beyond instrument effects, field measurements showed substantial temperature-driven fluctuations of soil water content and matric potential, which complicated data interpretation.展开更多
Groundwater recharge significantly affects soil moisture redistribution through capillary rise. In this study,the soil matric potential at depths of 5, 10, 20 and 30 cm above the groundwater tables of 10, 30 and 60 cm...Groundwater recharge significantly affects soil moisture redistribution through capillary rise. In this study,the soil matric potential at depths of 5, 10, 20 and 30 cm above the groundwater tables of 10, 30 and 60 cm weremeasured for 5 d. Soil hydraulic properties were analyzed by using the Philips and de Vries model. Results showedthat evaporation mainly influenced the matric potential of the shallow layer at the 5 cm depth regardless of the saturationof the layer. Groundwater recharge mainly affected soil moisture at the depth of 20 cm or more. A constant matricpotential layer existed between the evaporation front and capillary rise front where moisture content did not change.The isothermal-liquid hydraulic conductivity （KLh） and the thermal-vapor hydraulic conductivity （KvT） were thedominant hydraulic conductivities in the liquid and vapor phases. At the groundwater table depths of 10, 30 and 60 cm,the mean peak values of KLh were 2.32×10^-7, 1.63×10^-7 and 0.29×10^-7 m/s, respectively, whereas the mean peakvalues of KvT were 2.7×10^-7, 2.4×10^-7 and 1.8 ×10^-7m/s, respectively.展开更多
文摘土体冻结过程中不同位置液态水的能量差引起了水分迁移与重分布,进而引发冻胀,关于势能差驱动下的冻土水分迁移问题一直由于技术手段的匮乏而没有完全解决。利用新近推出的可用于冻土水热研究的p F meter基质势传感器与5TM水分传感器,实时监测研究饱和青藏红黏土单向冻结过程中基质势-液态含水率-温度-含冰量-水分迁移量-冻胀变形之间在时间、空间上的耦合变化关系。结果表明:土体温度场变化引起内部液态水相变,打破了原有的能量平衡,试验结束后12~14 cm土样高处含水率最高达到55%,靠近冻融交界面处(10 cm)的未冻区含水率减小至25.8%,水分整体向冷端发生迁移;土体冻胀的快慢及冻胀量大小与水分迁移速率及数量具有线性关系;试验后土体内总含水率的分布与分凝冰透镜体的分布一致,已冻区液态含水率的分布与温度梯度近似成线性关系,未冻区液态含水率的分布与水分的迁移量有关,与温度梯度无关。此外,温度场对水分场的变化具有诱导作用但二者并不同步,当冻结速率减小到一定程度时水分才开始迁移,第10小时后温度场趋于稳定而水分迁移并未停止。研究成果揭示了土体单向冻结过程中液态水、基质势、温度等物理参数的动态变化过程及内在联系,为冻胀机制的研究以及冻胀模型的建立提供了试验基础。
文摘土壤水分特征曲线模型作为实验测定土壤水分特征数据的一种替代方法,因其具有计算方便快捷和便于嵌入数值模拟程序的优点,开始受到越来越广泛的关注。虽然文献中存在众多的土壤水分特征曲线模型,但是这些模型的适用范围及拟合性能尚不明确。为了获得更加准确适用的土壤水分特征曲线,在实际应用中通常需要花费大量时间和精力去测试各种模型。为了解决上述问题,在国内外研究成果的基础上收集整理了12种典型的土壤水分特征曲线模型,并利用包含不同质地、有机质含量及容重的8种土壤的实测土壤水分特征数据来评估比较这些模型的模拟性能。模型性能通过均方根误差(RMSE)、平均偏差(AD)、AIC准则(Akaike Information Criterion)和纳什效率系数(NSE)4个指标评估。研究结果表明:大部分的模型能够提供比较接近于实际的拟合结果,评价指标值也比较相近。其中,KCGS2006(包含3个参数)和K1999模型(包含2个参数)拟合效果最好,而Gregson1987(包含1个参数)的拟合效果最差。该研究可以深入了解各种土壤水分特征曲线模型的适用性与局限性,更好地为生态环境建设和农业可持续发展研究中土壤水力参数的选取提供依据和参考。
文摘Soil water sensors are commonly used to monitor water content and matric potential in order to study hydrological processes such as evaporation. Finding a proper sensor is sometimes difficult, especially for measurements in topsoil, where changes of temperature and soil water dynamics occur generally with greater intensity compared to deeper soil layers. We assessed the perfor-mance of Hydra Probe water content sensors and MPS-1 matric potential sensors in topsoil in the laboratory and in the field. A common soil-specific calibration function was determined for the Hydra Probes. Measurement accuracy and sensor-to-sensor variation were within the manufacturer specification of ±0.03 m3·m-3. Hydra Probes can operate from dry to saturated conditions. Sensor-specific calibrations from a previous study were used to reduce sensor-to-sensor variation of MPS-1. Measurement accuracy can be expressed by a mean relative error of 10%. According to the manufacturer, the application range of matric potential readings is from -10 kPa to -500 kPa. MPS-1 delivered also values beyond this range, but they were not reliable. Sensor electronics of the MPS-1 were sensitive to ambient temperature changes. Beyond instrument effects, field measurements showed substantial temperature-driven fluctuations of soil water content and matric potential, which complicated data interpretation.
基金Supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China(No.2012BAC07B02)
文摘Groundwater recharge significantly affects soil moisture redistribution through capillary rise. In this study,the soil matric potential at depths of 5, 10, 20 and 30 cm above the groundwater tables of 10, 30 and 60 cm weremeasured for 5 d. Soil hydraulic properties were analyzed by using the Philips and de Vries model. Results showedthat evaporation mainly influenced the matric potential of the shallow layer at the 5 cm depth regardless of the saturationof the layer. Groundwater recharge mainly affected soil moisture at the depth of 20 cm or more. A constant matricpotential layer existed between the evaporation front and capillary rise front where moisture content did not change.The isothermal-liquid hydraulic conductivity （KLh） and the thermal-vapor hydraulic conductivity （KvT） were thedominant hydraulic conductivities in the liquid and vapor phases. At the groundwater table depths of 10, 30 and 60 cm,the mean peak values of KLh were 2.32×10^-7, 1.63×10^-7 and 0.29×10^-7 m/s, respectively, whereas the mean peakvalues of KvT were 2.7×10^-7, 2.4×10^-7 and 1.8 ×10^-7m/s, respectively.
