Experiments with capillary fringes (CF) in quartz sand were conducted. The respiratory activity, cell growth or the biofilm formation by different soil bacteria in the CF were examined. Highest bacterial activity and cell adsorption on the sand particles were detected between the almost water saturated and unsaturated CF-region. Primarily in this transition zone the bacteria strongly influenced the vertical oxygen diffusion and reduced the hydraulic conductivity due to biological clogging.
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