再生水灌溉条件下农田土壤优先流的演化过程与驱动机理研究

Reclaimed water irrigation saves precious water resources and alleviates the shortage of agricultural water supply. Besides, the nutrients and microelements in the reclaimed water promote the crop growth and grain output. However, the organic and inorganic materials in the reclaimed water will change the soil structure and characteristics, result in the evolution of preferential flow and transport behavior and the deposition of infiltrated materials. All these will enhance the contaminant risk of reclaimed water irrigation projects. To reveal the evolution and driving mechanism for the preferential flow in unsaturated soil under reclaimed water irrigation, laboratory experiments using repacked soil columns are designed to study and illustrate the impacts of suspended solids, oils, surfactants and salts on the change of soil structure and characteristics and the evolution of preferential flow. The effects of soil type, reclaimed water irrigation patterns and contaminants concentration on these impacts will also be studied and clarified. Besides, plot experiments irrigated with reclaimed water are also designed to be conducted in field to study the synthetic action of all the materials in the reclaimed water on the change of soil structure and characteristics and also the evolution of preferential flow. This research is very valuable for the design of reclaimed water irrigation schedule, contaminant risk control and eco-environment protection.

再生水灌溉农田既可节约宝贵的水资源、缓解农业用水紧缺，同时再生水中的多种营养元素和微量元素可促进作物生长、提高粮食产量。但再生水中的污染物质进入农田后将引起土壤结构和性质的变化，进而改变水和污染物质在农田土壤中的输移路径和沉积分布，从而增大再生水农田灌溉工程的环境污染风险。为揭示再生水灌溉条件下农田土壤优先流结构的演化过程和驱动机理，本项目将通过室内土柱试验系统研究再生水中的悬浮固体、油脂、表面活性剂和盐分对土壤结构和性质的影响以及对土壤优先流结构演化的作用，阐明这些影响和作用随土壤类型、再生水灌溉模式以及污染物浓度的变化特征。此外，本项目研究也将开展再生水农田小区灌溉试验，研究再生水中多种污染物质的综合作用对土壤结构和性质的影响以及对土壤优先流结构演化的驱动机理。本项目研究对再生水农田灌溉制度制定、污染风险控制和生态环境保护都具有重要的研究意义。

再生水灌溉农田缓解了农业用水紧缺，但再生水中的污染物质进入农田后增大了环境污染风险。本项目研究了再生水中的悬浮固体、盐分、油脂和表面活性剂对土壤结构性质和水流运动特征的影响。研究结果表明，（1）灌水中悬浮固体浓度越大，受灌土壤容重越大、孔隙率和地表入渗能力越小、优先流的非均匀性越强；低频率、大定额的灌水使悬浮固体更多聚集在表层土壤中，导致土壤容重增大、孔隙率减小，诱发土壤分层，加剧优先流的非均匀性；清水淋洗无法将灌水引入的悬浮固体淋洗至深层土壤，不能改变土壤的板结趋势。（2）适度的盐分浓度、较低的灌水频率但较大的灌水定额、含盐灌溉水-清水交替灌溉均有利于提升土壤团聚体的稳定性、抑制土壤板结、改善受灌土壤的地表入渗性能、降低优先流的非均匀性。（3）随灌水进入到受灌土壤中的油脂主要集中在优先流通道中快速运动，优先流湿润锋处的土壤油脂浓度较高且不受灌溉水中油脂浓度的影响；高频率、低定额的含油脂灌溉水灌溉有利于进入到受灌土壤中的油脂向深层土壤运动，使得斥水性土层厚度增大，导致优先流的非均匀性增大；油脂对受灌土壤团聚体的再团聚作用只有在其浓度较高时才能形成，含油脂灌溉水-清水交替灌溉因降低了受灌土壤的油脂浓度反而导致土壤团聚体分散和破碎。（4）随着再生水中的阴离子表面活性剂浓度的增大和灌溉频率的增大，受灌土壤容重减小、非毛管孔隙比和土壤团聚体稳定性增大、土壤斥水性增强、地表入渗能力降低、优先流的非均匀性增大；当再生水-清水交替灌溉中的清水淋洗频率增大时，受灌土壤容重增大、非毛管孔隙比和土壤团聚体稳定性降低，但却降低了土壤的斥水性、增大了地表入渗能力并降低了优先流的非均匀程度，有利于节省灌水时间、提高灌水效率。本项目研究成果对再生水农田灌溉制度制定、污染风险控制和生态环境保护都具有重要的研究意义。