温度对红壤水力学参数和水分入渗过程的影响

Temperature changes would alter physical and chemical properties of solid, liquid and gas items of soil, and also their interactions, which would affect the soil hydraulic properties, and ultimately affect the soil water infiltration, and this is particularly true for the clay soil. Clay soil is widely distributed in the southern China characterized by the red soil, where the rainfall was abundant and temperature fluctuates significantly around the year, which results in the significant temperature effects on water infiltration, but the mechanism and the effects were still unclear. The red soil widely distributed in the southern China was taken as the research object, which was used to study the temperature effects on soil hydraulic properties and soil water infiltration, depending on the laboratory analysis, field monitoring and numerical simulation. The mechanisms and main factors resulted in the hydraulic properties changes will be revealed, and the temperature dependent soil hydraulic properties model will be established, finally the effect of temperature on water infiltration will be quantified by the numerical simulation of modified HYDRUS model. The research results will enrich the theory of temperature effect on soil water movement, which could be used to provide theoretical supports for the accurate quantifying seasonal variations of hydrological process of red soil such as water infiltration and run off, and provide scientific supports for farmland precision irrigation and soil-water conservation.

温度变化会引起土壤固、液、气三相理化性质及其相互作用关系的改变，进而影响土壤水力学参数，最终影响水分入渗过程，而温度对粘重土壤的影响尤为显著。红壤作为典型粘重土壤广泛分布于我国南方地区，该区降雨丰沛，年内温度波动较大，水分入渗过程的温度影响效应明显，但影响的程度和机制尚不明确。本项目拟以南方红壤为研究对象，采用室内模拟分析、野外定位监测和数值模拟相结合的方法，研究温度对红壤水力学参数和水分入渗过程的影响：量化温度对红壤水力学参数的影响并揭示影响机制和主要因子，以此构建基于温度效应的红壤水力学参数模型；揭示温度对红壤水分入渗过程的影响规律，并在改进HYDRUS模型的基础上通过数值模拟的方式量化其影响程度。本课题的研究成果将丰富土壤水分运动的温度效应理论，可为准确量化红壤水分入渗、地表径流等土壤水文过程的季节性变化规律提供理论支撑，为农田精准灌溉和合理的水土保持措施制定提供科学依据。

温度变化会引起土壤三相理化性质及其相互作用关系改变，进而影响土壤水力学参数，最终影响水分运动过程。然而目前关于温度对土壤水力性质和水分运动过程的影响程度和机制尚不明确。本项目以广州、鹰潭、咸宁、常熟、荆州、封丘、沈阳、长武、安塞和张掖等地的土壤为研究对象，测定了不同温度条件下（5、15、25、35、45 oC）的饱和导水率、水分特征曲线和膨胀系数，发现温度对土壤饱和导水率的影响与质地有关，砂质土壤的饱和导水率随温度升高持续增大，较为粘重土壤的饱和导水率在低温段随着温度的升高而增加，其它土壤（红壤除外）在高温段保持不变或下降；温度的升高导致土壤持水能力降低，对于Van-Genuchten模型的拟合参数表现为θs、θr和n均随着温度的升高而减小，α随着温度的升高而增大，这种影响对粘重土壤更为明显。温度对土壤水力性质的影响除受水的粘滞系数和表面张力变化影响外，还与土壤的孔隙特征和膨胀系数有关，这些效应的叠加导致不同类型土壤呈现不同的变化规律。不同温度条件下的红壤土柱水分入渗实验证实温度影响了水分入渗过程，表现为湿润锋迁移速率随着温度的升高明显增加，相同深度的水分探针和水势探针在高温条件下更早探测到水分和水势变化。通过红壤旱地、稻田和林地的野外监测，获取了土壤剖面不同深度的温度、含水量和水势高频监测数据，证实温度效应在自然条件下存在且需要考虑，特别是对于旱地和上层土壤。考虑温度效应的HYDRUS模型进一步完善了以上样地的水分运动过程模拟，发现温度效应的存在导致2018年的径流减少，土壤蒸发、深层渗漏和储水量增加；非作物生育期的温度效应较小，且这一效应在旱地最为明显，稻田其次，林地最弱。本课题的研究成果丰富了土壤水分运动的温度效应理论，可为提高土壤水文过程模拟精度提供基础数据和技术支撑。