海涂围垦区土壤结构变化影响下钠盐运移水动力学过程试验研究

The soil in coastal region is characterized with high sodium salt content, poor structure, and different water-salt transport process from other soils. It is a major issue to raise appropriate measures for soil desalination and melioration on the basis of the rule of soil water-salt transport in high sodium soil, during the reclamation of coastal region. However, the information about soil water-salt transport in this special soil is not enough, especially, the interactions among the change of soil structure and processes of water-salt transport are not entirely clear for the high sodium soil. Based on field monitoring with transect uniform distributed points and grids points in reclamation areas, this project aims to characterize the spatio-temporal changes of soil structure and the main influencing mechanism. Field observation system for soil hydraulic model parameters will be established to quantify the transfer function relationships between soil hydraulic properties and soil structure. With a series of simulated rainfall experiments and filed plot monitoring, the study will get some important experiment data about dynamics of soil structure and soil water-salt transport, during the processes of rainfall (irrigation)-infiltration-redistribution of water and salt-groundwater dynamic-evopatration (transpiration). Finally,the study proposes to put forward the fitting methods for simulation of the dynamic processes of soil water-salt transport in farmland by taking into account of the heterogeneity of soil structure of high sodium salt soil. The project is expected to clearly detect the hydrodynamic mechanism of sodium salt transport with influencing of soil structure change in the coastal reclamation region. The results could deep the understanding of soil water-salt transport process in the specific soil of the region, and provide scientific bases for planning and designing of the irrigation-drainage engineering, as well as for the reasonable uses of soil and water resources in coastal reclamation region.

海涂土壤钠盐含量高、结构性差，水盐运移过程不同于一般土壤。根据高钠盐土壤水盐运移规律，提出适宜脱盐改土措施，是海涂围垦开发利用必须解决的重要问题。但现阶段该类型土壤水、溶质运移研究不够深入，特别是高钠盐条件下土壤结构变化与水盐运移过程交互影响机制尚不明确。本研究以沿海滩涂不同年限围垦区高钠盐土壤为研究对象，通过样带均匀布点与典型垦区网格布点监测相结合，研究围垦区高钠盐土壤结构特征及其变化的主导因子，量化土壤结构变化对水力参数的传递影响；结合室内模拟试验和小区定位监测，获取降雨（灌溉）-入渗-水盐再分布-地下水波动-蒸发（腾）过程中土壤结构变化与钠盐运移的重要试验数据，数值分析多尺度土壤结构-水力特性变化对水盐动态的影响，阐明高钠盐土壤结构发育和演变过程中钠盐运移的水动力学机理。研究成果可深化认识区域特定土壤类型的水盐运移过程，为围垦区灌排工程规划设计和区域水土资源合理利用等提供科学依据。

海涂土壤钠盐含量高、结构性差，水盐运移过程不同于一般土壤。根据高钠盐土壤水盐运移规律，提出适宜脱盐改土措施，是海涂围垦开发利用必须解决的重要问题。但现阶段该类型土壤水、溶质运移研究不够深入，特别是高钠盐条件下土壤结构变化与水盐运移过程交互影响机制尚不明确。基于此，本研究以江苏沿海滩涂不同时段围垦区土壤结构为研究对象，结合室内模拟试验和小区定位监测，围绕围垦区土壤结构变化影响下钠盐运移水动力学过程开展为期4年的研究。项目通过小波分析、贝叶斯等方法，获得围垦区不同尺度下的土壤盐分、结构等参数时空变异特性。通过围垦区不同垦殖年限、土地利用方式、不同剖面上的土壤结构表征量和盐分特征，构建了高钠盐土水力参数与土壤结构的传递函数关系，模型拟合效果较好。低含量的土壤盐分促进土壤粘粒凝聚，降低土壤容重，增加土壤孔隙，提高持水能力，土壤盐分对水分入渗和蒸发的抑制作用占主导地位；高含盐量条件下，孔隙结构破坏与盐分共同作用进一步降低入渗率和蒸发率。土壤钠盐含量显著增大坡面径流平均雷诺数和径流功率，减小坡面阻力系数。盐渍土结构变化（不同压实容重）导致坡面径流雷诺数和弗劳德数差异显著，雷诺数随容重增大而增大，弗劳德数随容重增大而减小，提高土壤容重和坡度均显著降低平均入渗速率。通过结构改良措施，丰富了土壤孔隙结构，抑制水分蒸发，提升土壤水分渗透性能，降低盐渍土盐分含量，增强了土壤保水能力。土壤饱和含水率随着µ-CT 孔隙度和各向异性度增大而增大，进气吸力值的倒数（α）随着平均孔隙直径和分形维数的增加而增加。基于土壤形态参数，利用分形维数法，模拟了土壤水力性质；通过考虑土壤孔隙结构变化，利用格子Boltzmann方法计算了土壤固有渗透率，模拟了盐渍土水分迁移动力学过程。根据盐土坡面侵蚀水动力学过程规律，构建了土壤结构变化影响下的盐土坡面降雨-径流-侵蚀水动力学模型，模拟值与实测值具有较好的一致性。项目研究了围垦区土壤结构改良下的作物生长效应，提出了一种海涂新垦区盐碱地快速脱盐改土剖面立体结构（专利号ZL201310246611.X）。