灌溉条件下土壤优先流对病原细菌迁移的影响机制

Preferential flow paths are the important passage of transport to deep soil or to groundwater of pathogenic bacteria. Based on field investigation, samples analysis, static batch test, soil column experiment and orthogonal design, Luancheng town irrigated with sewage effluents for nearly 50 years will be selected as study area in Shijiazhuang, Hebei province. Escherichia coli as a representative pathogenic bacteria will be studied using the technologies of computed tomography and tracer. This study will be aimed towards the distribution characteristics and migration mechanism of escherichia coli with preferential flow. The contents of this research are mainly composed of the following three parts. The first one is to investigate the types of preferential flow and macropore characteristics. The second is to present distribution characteristics of escherichia coli and its influence factors in preferential flow and matrix flow paths. The last one is to study the effect of sewage concentration, irrigation intensity, macropore type, initial water content and soil texture on the transport of escherichia coli, and to reveal the response mechanism of transport of escherichia coli to preferential flow under irrigation conditions. In this study, we will try to study the characteristics of soil physics, chemistry and biology in preferential flow paths and their correlation, which can enrich the foundation theory of soil preferential flow. On the other hand, we will study the different degree of impact of five factors on the transport of escherichia coli, and to reveal migration mechanism of escherichia coli in the preferential flow systems, which can provide scientific basis for effectively preventing transmission paths of pathogenic microorganism and protecting security of water resource.

优先流路径是病原细菌向深层土壤或地下水中迁移的重要通道。本研究拟采用野外调查、采样分析、静态批试验、土柱试验和正交试验相结合的方法，选择以近50年灌溉历史的石家庄栾城污水灌溉区为研究区，以病原细菌典型菌-大肠杆菌为研究对象，综合运用示踪剂示踪和CT扫描技术，系统研究优先流现象下大肠杆菌的分布特征及其迁移机制。研究土壤优先流类型及大孔隙特征，阐明优先流和基质流路径下的大肠杆菌分布特征及其影响因素，重点研究污水浓度、灌溉强度、孔隙类型、初始含水量、土壤质地等因素对大肠杆菌迁移的影响，揭示灌溉条件下大肠杆菌迁移对优先流的响应机制。本研究的开展，一方面研究优先路径下的土壤物理、化学和生物特征及其相互关系，从而丰富和发展土壤优先流的理论研究基础，另一方面研究5种因素对大肠杆菌迁移影响的不同作用程度，从而揭示优先流现象下大肠杆菌的迁移机制，为有效切断病原微生物的传播途径与维护水资源安全提供科学依据。

本研究通过野外调查、采样分析、土柱试验和CT扫描相结合的方法，选择以近50年污水灌溉历史的石家庄栾城为研究区，以病原细菌典型菌-大肠杆菌为研究对象，阐明土壤优先流类型及土壤大孔隙特征，系统研究优先流现象下大肠杆菌的分布特征及其迁移机制。研究结果表明：污水灌溉时间对土壤孔隙数和孔隙度产生了明显的影响，并且，随着污水灌溉时间的增加，下层土壤（20-40 cm）孔隙数和孔隙度越低，但是对土壤孔隙形态并无明显的影响；研究区土壤孔隙参数受到土壤真菌数量和全磷含量的显著影响。研究区土壤存在明显的优先流现象，其类型主要表现为指流；污水灌溉对土壤优先流现象存在明显的影响效应，土壤总染色面积以荒地最大，清灌区耕地次之，污灌区耕地最小；优先流现象对土壤特性的分布产生了深刻的影响。污灌区耕地0-400 cm土层中大肠杆菌分布受到钠离子含量、脲酶活性和磷酸酶活性的显著影响，而林地0-400 cm土层中大肠杆菌分布受到放线菌数量的显著影响；与填充土柱相比，原状土柱中大肠杆菌的迁出数量较多，表明优先流现象对大肠杆菌的迁移具有显著的影响；与饱和条件相比，非饱和条件下原状土柱中大肠杆菌的迁出数量较多，表明土壤的初始含水量对优先流现象下的大肠杆菌迁移具有明显的影响。