The unsaturated zone plays a significant role in protecting groundwater resources from microbial contaminants. The mechanisms governing bacteria transport and retention in aggregated soils are still not fully understood and quantified. This study aims to investigate transport and retention in undisturbed calcareous soils under both saturated and unsaturated conditions. Series of transport experiments with well-controlled suctions and flow rates were performed. The breakthrough curves of bacteria and a nonreactive tracer (Cl) were obtained. The bacteria were then quantified in different layers of soil. HYDRUS-1D two-site depth-dependent deposition model was employed to simulate transport and retention of bacteria. HYDRUS-1D two-site depth-dependent deposition model fit the observed data well (R=0.99). Results revealed that the average ratio of detachment to attachment rate was 0.028 and 0.016 under saturated and unsaturated flow conditions, respectively, demonstrating nearly irreversible attachment of cells. Increasing depth dependent-deposition coefficient () in unsaturated soils was attributed to straining and film straining. The majority of bacteria were deposited nearby the inlet of soil columns, and the rate of retention diminished with depth. Bacterial removal rate was 2.5 times higher under unsaturated than under saturated condition. High removal rate of bacteria under unsaturated flow was attributed to retention of bacteria to film straining, air-water interface, and also attachment to CaCO minerals that contained preferred sites for negatively charged cells.

中文翻译：

---

饱和和非饱和条件下原状钙质土壤中细菌的迁移和沉积


非饱和带在保护地下水资源免受微生物污染方面发挥着重要作用。控制聚集土壤中细菌运输和保留的机制尚未完全理解和量化。本研究旨在研究饱和和非饱和条件下原状钙质土壤的迁移和保留。进行了一系列具有良好控制的吸力和流速的运输实验。获得了细菌和非反应示踪剂 (Cl) 的穿透曲线。然后对不同土壤层中的细菌进行定量。采用 HYDRUS-1D 两点深度依赖沉积模型来模拟细菌的运输和滞留。 HYDRUS-1D 两点深度相关沉积模型与观测数据吻合良好（R=0.99）。结果显示，在饱和和不饱和流动条件下，脱离与附着率的平均比率分别为0.028和0.016，表明细胞的附着几乎是不可逆的。非饱和土中深度相关沉积系数 () 的增加归因于应变和薄膜应变。大多数细菌沉积在土柱入口附近，并且保留率随着深度的增加而降低。不饱和条件下的细菌去除率是饱和条件下的2.5倍。在不饱和流下细菌的高去除率归因于细菌保留在薄膜应变、空气-水界面上，以及附着在含有带负电细胞的首选位点的 CaCO 矿物质上。