Chen Jing, Yang Liqiong, Chen Xijuan, Ripp Steven, Zhuang Jie
Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, China.
College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China.
Front Microbiol. 2022 Feb 21;13:730075. doi: 10.3389/fmicb.2022.730075. eCollection 2022.
Transport of pathogenic bacteria from land surface to groundwater is largely influenced by rainfall intensity and geochemical and structural heterogeneities of subsurface sediments at different depths. It has been assumed that the change in rainfall intensity has different effects on bacterial transport as a function of soil depth. In this study, repacked and intact column systems were used to investigate the influences of pore water velocity on the transport of 652T7 through a loamy soil collected from varying soil depths. The soils differed in geochemical properties and soil structures. The concentrations of bacteria in soil and liquid samples were measured using plate counting method. The breakthrough percentages of 652T7 increased with pore water velocity at each depth in both intact and disturbed soils. Among the different soil depths, the largest velocity effect was observed for the transport through the top soil (0-5 cm) of both disturbed and intact soil profiles. This depth-dependent effect of pore water velocity was attributed to down gradients of soil organic matter (SOM) and iron oxide contents with depth because SOM and iron oxides were favorable for bacterial attachment on soil surfaces. In addition, less bacteria broke through the disturbed soil than through the intact soil at the same depth, and the pore water velocity effect was stronger with the disturbed than intact soils. Specifically, the maximum C/C (i.e., ratio of effluent to influent concentration) doubled (i.e., from 0.36 to 0.76) in the 0-5 cm intact soil columns and tripled (i.e., from 0.16 to 0.43) in the 0-5 cm repacked soil columns. This structure-dependent effect of pore water velocity was attributed to larger pore tortuosity and a narrower range of pore sizes in the disturbed soil than in the intact soil. These findings suggest that change in pore water velocity could trigger bacterial remobilization especially in surface soils, where more bacteria are retained relative to deep soils.
致病细菌从地表向地下水的迁移在很大程度上受降雨强度以及不同深度地下沉积物的地球化学和结构非均质性影响。一般认为，降雨强度的变化对细菌迁移的影响会因土壤深度而异。在本研究中，使用重新装填和原状柱系统，研究孔隙水速度对从不同土壤深度采集的壤土中652T7迁移的影响。这些土壤在地球化学性质和土壤结构方面存在差异。采用平板计数法测量土壤和液体样品中的细菌浓度。在原状土和扰动土中，652T7在各深度处的穿透百分比均随孔隙水速度增加。在不同土壤深度中，对于扰动土和原状土剖面的表层土壤（0 - 5厘米），观察到孔隙水速度对迁移的影响最大。孔隙水速度的这种深度依赖性效应归因于土壤有机质（SOM）和氧化铁含量随深度的下降梯度，因为SOM和氧化铁有利于细菌附着在土壤表面。此外，在相同深度下，扰动土中穿透的细菌比原状土中的少，且扰动土中孔隙水速度的影响比原状土更强。具体而言，在0 - 5厘米原状土柱中，最大C/C（即流出物与流入物浓度之比）翻倍（即从0.36增至0.76），在0 - 5厘米重新装填土柱中则增至三倍（即从0.16增至0.43）。孔隙水速度的这种结构依赖性效应归因于扰动土中比原状土更大的孔隙曲折度和更窄的孔径范围。这些发现表明，孔隙水速度的变化可能引发细菌的再迁移，尤其是在表层土壤中，相对于深层土壤，表层土壤中保留了更多细菌。
