Controlling soil hydraulic conductivity with the control of microbial activity

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This research aims at developing a technique to control water permeability of soils to required values by multiplying the microbe in soil or making it decrease. In a model experiment, hydraulic conductivity changes of the glass beads of different diameters were measured. Hydraulic conductivity at the upper layer decreased more rapidly for smaller particle diameter beads, because the nutrient was mainly consumed at the upper layer resulting in less nutrient at the lower layer. In on-site measurement at Bibai peatland in Hokkaido District, methane gas produced by bacteria is accumulated in the ground. To simulate this methane producing process, a laboratory column experiment was conducted. When the groundwater level was lowered by 10cm, the redox potential at the 5cm depth decreased to less than -150mV at 6 day after the start of percolation. As a result, a lot of methane emission into the atmosphere was observed. Based on the result of the above experiment and on-site measurement a mathematical model explaining the hydraulic conductivity decrease by microbial activity was built. The difference in particle diameter influences microbial growth rate and a colony formation phenomenon was expalined by this model.