EFFECT OF MICROORGANISMS ON PERMEABILITY OF SOIL UNDER PROLONGED SUBMERGENCE

Publisher Website
Google Scholar
Abstract
Laboratory permeability and field infiltration tests conducted under conditions of prolonged submergence indicate continuous permeability changes with time. On wetting dry soil it often decreases slightly and then increases to a maximum, usually within a few days. The max. is reached when all entrapped air is eliminated from the pores by solution in the percolate. Thereafter, the permeability decreases rapidly at first, then more slowly until after 20 to 30 days the soil transmits water only very slowly if at all. For practical purposes, such as in water-spreading for underground storage in valley floor areas, the soil virtually seals up. Under continuous submergence, the first few inches of the soil is invariably the zone of limiting permeability. Addition of disinfectants to water used in long-time laboratory permeability tests indicated a biological factor as the cause of soil-sealing. This theory was checked by the following methods: (1) A method of sterilizing soil (air-dry) with ethylene oxide gas which does not appreciably alter physical properties of the soil, and (2) A closed-sterile-percolation system for continuously supplying filtered water containing 10 ppm. of HgCl2 to sterile soils in glass percolation tube permeameters. Evidence obtained on sterile Hanford loam and Exeter and Hesperia sandy loam soils indicated conclusively that microorgnsims are the cause of decreased permeability or soil-sealing under prolonged submergence, either by clogging soil pores with the products of growth (cells, polysaccharides), by a dispersion resulting from their attack on the organic materials which bind soil particles into aggregates, or a combination of these factors. Physical disintegration of soil aggregates appears to play no part in the process.

This publication has 2 references indexed in Scilit: