Elsevier

Engineering Geology

Volume 287, 20 June 2021, 106101
Engineering Geology

Effects of bacterial activity on the saturated hydraulic conductivity of remolded loess

https://doi.org/10.1016/j.enggeo.2021.106101Get rights and content

Highlights

  • Saturated hydraulic conductivity decreased by 81–93% due to bacterial activities.

  • Delayed effect between linear reduction of hydraulic conductivity and exponential growth of bacteria.

  • Reduction of hydraulic conductivity is mainly due to bacterial growth in inlet layer.

Abstract

Loess is widely used as a construction material in engineering projects on the Loess Plateau of China but is regarded as one of the most problematic soils due to water sensitivity. Hydraulic conductivity (K) is an essential parameter in assessment of water transfer in porous media. However, the influence of bacterial activity on the saturated permeability of remolded loess is still unclear and rarely being studied. We systematically studied the effects of Gram-negative bacterial activity (a common bacteria in the loess region) on the hydraulic properties of remolded loess, with the aim to better understand water flow through loess. A series of laboratory experiments were conducted to identify the variation in hydraulic conductivity under various bacterial inoculation and carbon constraint conditions. The results indicated that the K was relatively stable (0.14–0.16 m/d) at the initial phase and decreased by 81–93% reaching 0.01–0.05 m/d at the end of the experiments. The variation of hydraulic conductivity can be divided into the unaffected stage, linear reduction stage and stable stage. The growth of bacteria and the accumulation of extracellular polymeric substances occupied the pores between soil particles in the sample, which reduced the porosity and lead to the decrease of K. Higher available carbon contents and greater initial inoculum sizes speeded up the process of hydraulic conductivity reduction. The delayed effect was observed between rapid decline of hydraulic conductivity and exponential growth of bacteria. It should be highlighted that the reduction of hydraulic conductivity in the soil columns was mainly dependent on clogging in the inlet layer. Our findings provide a better insight into the change of hydraulic conductivity related to bacterial activities, and promote the reorganization of water cycle uncertainty and the prevention of engineering geological disasters in loess areas.

Introduction

Loess, an aeolian silt with engineering geological significance, accounts for approximately 10% of the terrestrial surface of the earth that widely distributed in Asia, Europe, and North America. China's Loess Plateau (CLP) has the deepest and largest loess deposition area in the world, with a total coverage area of about 440,000 km2 and a maximum thickness of more than 300 m (Liu, 1985; Sun, 2005). As the “cradle of Chinese civilization”, the CLP covers 6.7% of the total area of the country and is also home to about 10% of the total population. In a dry state, loess has high strength and small deformation, but it is considered to be one of the most problematic soils because its structure collapses when it is wet (Assallay et al., 1997; Ma et al., 2017). Due to water sensitivity, loess areas often suffer from engineering disasters closely related to water (e.g., land subsidence, ground fissure, landslide, and piping) (Hosseinalizadeh et al., 2018; Smalley and Dijkstra, 1991; Wang et al., 2020; Zhuang et al., 2018). With the large-scale construction of projects in recent years, such as high fill foundation, expressway, high-speed railway, embankment and water conservancy projects, it is becoming more and more important to understand the flow of water in loess for engineering application and geological disaster prevention in loess areas.

Saturated soil hydraulic conductivity (K) is an essential parameter to measure water flow through the soil (Chen et al., 2020; Gómez-Hernández and Gorelick, 1989; Piña et al., 2019). Historically, it is usually regarded as a constant value at given conditions over time (Baveye et al., 1998; Chen and Qian, 2017; Chen et al., 2020; Qian et al., 2020; Sanchez-Vila et al., 2006). There is no exception for loess. However, it has been determined that microorganisms are widely distributed in soil. Microorganisms can develop biofilms in many natural and engineered porous media systems. Growth of bacteria in soil could lead to substantial decrease in porosity and permeability due to the biofilm-induced modifications of pore-space geometry (Baveye et al., 1998; Brovelli et al., 2009; Gowrisankar et al., 2017; Khaleghi and Rowshanzamir, 2019). The resultant clogging may decrease water flux and limit nutrient supply, thereby causing a restriction in microbial activity (Arnon et al., 2005). Bielefeldt et al. (2002) and Seifert and Engesgaard (2007), in sand column experiments, found that microbial growth caused 2–4 orders of magnitude decrease in K. Kirk et al. (2012) confirmed that biomass largely remained intact after acidification and continue to reduce K, even when considerable death occurred. Compared to phosphorous content and temperature, carbon source was mentioned as the major cause for biofilm growth (Calderer et al., 2014; Xia et al., 2014). In this regard, the common assumption of unchanged K may be not appropriate and may increase uncertainty in describing, simulating and predicting water and even solute transports in loess. To date, identifying the anisotropy of hydrological conductivity and microstructural changes for loess has been the target of many studies (Feng et al., 2020; Gao et al., 2018; Li and Li, 2017; Shao et al., 2018; Wang et al., 2020; Wang et al., 2018; Xu et al., 2020), while the effect of microbial activity on the hydraulic conductivity of loess has very limited investigation. The knowledge gap causes that there is still little experience to study influence of biomass growth on water movement and to evaluate consequential risk of geohazards in loess engineering.

In this study, the effects of bacterial activity on the hydraulic properties of loess soil were quantified for the first time. Malan loess (Q3), as the most widely distributed loess on the CLP, is often used as the construction material in engineering projects. The main objectives of this study were to explore the complex interactions between hydraulic conductivity and bacterial activity in Malan loess, with the aim to increase our understanding of the mechanisms of interaction in soil-water-microbe systems. Our findings will enable a new insight into the variation of hydraulic conductivity in loess soil at the experimental scale. It also provides a basis for studying the influence of bacterial activities on water migration and the resultant uncertainty in loess areas.

Section snippets

Soil sample collection

Malan loess sampled from Jingyang County of Shaanxi Province, in the middle of China's Loess Plateau, was used in the experiments described below (Fig. 1). The samples were thoroughly mixed, air-dried, and subsequently sieved according to the specification of the soil test (MWRPRC and the Ministry of Water Resources of the People's Republic of China, 1999). Particle size analysis was carried out via a laser particle size analyzer (Bettersize2000, China). The basic physical soil properties are

Changes in hydraulic conductivity

The reduction of saturated hydraulic conductivity for all the lab-scale columns was observed (Fig. 5). Earliest measured values of the saturation hydraulic conductivities (about 10 h) ranged from around 0.14 to 0.17 m/d. As the experiments proceeded, linear decrease of K was observed and then the values tended to be relatively stable. Similar patterns of K reduction were detected in all columns, although the final K values widely ranged between 0.01 and 0.05 m/d. Obviously, K reduction in the

Mechanism of hydraulic conductivity reduction

The accumulation of bacterial cells and the formation of biofilms (extracellular polymeric substance excretion, EPS) can modify the pore-space geometry, resulting in an increase of the resistance of water flow (Engesgaard et al., 2006; Kim et al., 2010). To explore the impacts of various nutrient supply conditions on EPS production, the EPS production by G- was measured using a fluorescence microscope (Leica DMi8-M, Germany). Fig. 7 shows the distribution of bacterial cells and EPS in the loess

Conclusions

The study evaluated the effect of bacterial activity on hydraulic conductivity for the remodeled loess. The variation of hydraulic conductivity was divided into the unaffected stage, linear reduction stage and stable stage. K reduction was unobvious in the specimens at the beginning of the experiments. Then the pores between the soil particles in the specimens were occupied by the growth of Gram-negative bacteria and the accumulation of EPS, which reduced the porosity. It was the main reason

Author statement

Jie Chen: Conceptualization; Data curation; Formal analysis; Funding acquisition; Methodology; Project administration; Supervision; Validation; Writing - original draft; Writing - review & editing. Hui Qian: Conceptualization; Data curation; Funding acquisition; Methodology; Project administration; Supervision; Writing - original draft; Writing - review & editing. Mi Yang: Investigation; Methodology; Software; Supervision; Validation; Writing - original draft. Jinyi Qin: Investigation;

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This research is supported by grants from the National Natural Science Foundation of China (41790441, 41931285, 41761144059 and 41572236), China Postdoctoral Science Foundation (300204000181), Special Fund for Basic Scientific Research of Central Colleges in Chang'a University (300102290102 and 300102299506). Anonymous reviewers and the Editor are sincerely acknowledged for their useful comments.

References (55)

  • J.W. Kim et al.

    Biofilm morphology as related to the porous media clogging

    Water Res.

    (2010)
  • M.F. Kirk et al.

    Variation in hydraulic conductivity with decreasing pH in a biologically-clogged porous medium

    Int. J. Greenh. Gas Control

    (2012)
  • X.a. Li et al.

    Quantification of the pore structures of Malan loess and the effects on loess permeability and environmental significance, Shaanxi Province, China: an experimental study

    Environ. Earth Sci.

    (2017)
  • D. Liu et al.

    The restoration age of Robinia pseudoacacia plantation impacts soil microbial biomass and microbial community structure in the Loess Plateau

    CATENA

    (2018)
  • F. Ma et al.

    Water sensitivity and microstructure of compacted loess

    Transp. Geotechnics

    (2017)
  • V.L. Morales et al.

    Are preferential flow paths perpetuated by microbial activity in the soil matrix? A review

    J. Hydrol.

    (2010)
  • A. Piña et al.

    Analysis of the scale-dependence of the hydraulic conductivity in complex fractured media

    J. Hydrol.

    (2019)
  • S.J. Pogorzelski et al.

    In-situ surface wettability parameters of submerged in brackish water surfaces derived from captive bubble contact angle studies as indicators of surface condition level

    J. Mar. Syst.

    (2013)
  • H. Qian et al.

    Assessing groundwater pollution and potential remediation processes in a multi-layer aquifer system

    Environ. Pollut.

    (2020)
  • R. Samsó et al.

    Modelling bioclogging in variably saturated porous media and the interactions between surface/subsurface flows: Application to Constructed Wetlands

    J. Environ. Manag.

    (2016)
  • D. Seifert et al.

    Use of tracer tests to investigate changes in flow and transport properties due to bioclogging of porous media

    J. Contam. Hydrol.

    (2007)
  • X. Shao et al.

    Collapse behavior and microstructural alteration of remolded loess under graded wetting tests

    Eng. Geol.

    (2018)
  • I.J. Smalley et al.

    The Teton Dam (Idaho, U.S.A.) failure: problems with the use of loess material in earth dam structures

    Eng. Geol.

    (1991)
  • Q. Tang et al.

    Impact of biological clogging on the barrier performance of landfill liners

    J. Environ. Manag.

    (2018)
  • W. Wang et al.

    Spatial variation of saturated hydraulic conductivity of a loess slope in the South Jingyang Plateau, China

    Eng. Geol.

    (2018)
  • H. Wang et al.

    Non-darcian flow in loess at low hydraulic gradient

    Eng. Geol.

    (2020)
  • L. Xia et al.

    Influences of environmental factors on bacterial extracellular polymeric substances production in porous media

    J. Hydrol.

    (2014)
  • Cited by (0)

    View full text