再生水灌溉亚热带土壤水力特性演化及水盐运移模拟研究

Combined issues of seasonal drought and water shortage due to pollution in the Subtropical zone in Southern China are increasingly prevalent. Based on the five kinds of typical subtropical soils- - red soil, yellow brown soil, paddy soil, purple soil and moisture soil, the research objective will be to investigate the influence of reclaimed water quality characteristics(EC/SAR/pH)on soil physical and chemical parameters by multiple research methods, including soil column leaching experiments, dynamic monitoring the water and salinity transport under alternating wetting and drying irrigation regimes with rainfall interspersed throughout the irrigation season, in situ infiltration characteristics measurements and numerical simulation methods. The influence of renewable water quality on hydraulic conductivity characteristics in soils will also be discussed. We hope to identify the irrigation water quality impacts on soil structure evolution under alternating drying and wetting events, and quantify the interrelationship of soil physical and chemical properties, irrigation water quality and soil hydrodynamic parameters. These parameters will be used to establish pedotransfer functions of soil hydraulic parameters for laboratory soils and apply them for field based soils under impacting irrigation water quality. Based on the analysis of the existing UNSATCHEM model, a conceptual model to predict water and salt migration will be developed, suitable for the subtropical area being studied with reclaimed water irrigation. The quantitative description of influence of irrigation quota and water quality on the law of soil water movement and salt accumulation will be given by using this model. This project research results will contribute to determination of threshold valued of reclaimed water use and provide a theoretical basis for adjusting and controlling patterns of water and salt migration, further enriching and improving the evaluation of water and soil environment influences by using recycled water.

我国亚热带南方地区季节性干旱与水质性缺水的双重问题日趋突出。本项目以再生水资源化利用为目标，选择红壤、黄棕壤、水稻土、紫色土和潮土等5种亚热带典型土壤为研究对象，以深刻认识再生水水质（EC/SAR/pH）对灌溉土壤理化特性影响为主线，通过土柱入渗淋溶试验，模拟降雨介入灌溉-干旱交替作用土槽试验，田间原位导水特性测定试验以及数值模拟等手段，探讨不同类型再生水灌溉水质对土壤水力学特征影响机理；揭示干湿交替作用下灌溉水质对土壤结构演化影响机理；定量土壤理化特性、灌溉水质与土壤水动力参数内在关系并尝试建立灌溉水质影响下扰动土与原状土的水力参数传递函数；在解析UNSATCHEM模型基础之上，建立适用于亚热带地区再生水灌溉水盐运移模型，定量描述灌溉定额及水质对土壤水分运动及盐分累积的影响规律。研究结果可为确定最佳的再生水利用阈值和水盐调控模式提供理论依据，并丰富和完善再生水利用的水土环境效应评价体系。

我国亚热带南方地区季节性干旱和水质性缺水的双重问题日趋突出，这为南方地区再生水灌溉利用，缓解水资源压力提供新途径。携带大量盐类物质的再生水长期灌溉对受纳土体的理化特性产生不可预测的潜在危害值得关注。本项目选择红壤、水稻土、紫色土和潮土等4种亚热带典型土壤为研究对象，研究发现，钠盐溶液处理使土壤微小孔隙所占比例增加，提高了各土壤的持水能力。土壤粘粒含量、交换性铁、铝含量对土壤水分运动主要起抑制作用，而粉粒含量、交换性钙、镁含量则起促进作用，钠盐加快了粘性潮土、沙性潮土、水稻土中水分运动，却抑制了红壤和紫色土水分扩散，钠盐浓度越高，其相对土壤水分扩散率越小。再生水入渗使得红壤、紫色土、水稻土的相对水分扩散度随含水率的增加呈现减小的趋势，而潮土的情况正好相反。长时间再生水连续灌溉和交替灌溉条件下4种土壤的容重、机械颗粒组成、土壤团聚体、土壤EC、pH、SAR、阳离子、阴离子、有机质、TN、TP等主要理化性质均发生不同程度演变。土壤饱和导水率与交换性钾、钠、钙、镁、EC、pH、容重等均呈极显著负相关。再生水灌溉改变了土壤持水特性，加速了土壤孔隙大小、数量及其分布的演变，再生水浓度和灌溉模式是影响了土壤导水特性变化的重要因素。再生水的pH、EC及SAR均与土壤有效含水率存在显著的相关性。进一步揭示了再生水中化学成分浓度越高，土壤斥水持续时间越长，斥水性差异性越显著；土壤盐分含量、粉粒含量和pH值是红壤斥水性的关键影响因素。再生水灌溉后土壤裂隙发育均随含水率的降低而增大，并且连通性增强，其主要几何指标变化规律均有所不同，其中变化最快的含水率区间均在20%之前，在含水率小于10%以后，4种土壤的裂缝几乎不再发生变化，但4种土壤受不同浓度再生水的影响程度存在差异。研究结果为南方开展资源节约型、环境友好型的再生水灌溉利用提供参考，为再生水灌溉和水盐调控模式提供理论依据，并丰富和完善再生水利用的水土环境效应评价体系。