9 April, 2001
C. M. (Mike) Reynolds, Research Soil Scientist, Bioremediation
Specializing in soil microbiology with a background in soil science, Mike Reynolds is conducting research at the Cold Regions Research and Engineering Laboratory (CRREL); Hanover, New Hampshire aimed at remediating contaminated soil. Upon coming to CRREL, Dr. Reynolds applied his expertise in soils to help the Army and DoD find cost effective ways to treat contaminated soils in cold regions, such as remote installations from the cold war era. Dr. Reynolds and his colleagues at CRREL, research microbiologist David Ringelberg, and Research Technicians Larry Perry and Karen Swarts-Foley, link microbiology with chemistry as they increase our ability to beneficially influence soils.
The underlying commonality of the soil microbiology and bioremediation research is to enhance natural phenomena so that we can more economically treat sites. Field demonstrations, three in Alaska and the two in Korea, are all faced with limited resources for treating contaminated soils. Cold temperatures in Alaska prove challenging for conducting remediation of contaminants, but both Alaska and Korea have manpower and resource limitations. Cleanup is costly due to the remoteness of the sites and limited alternatives. In cold regions, costs are further escalated because of the short treatment season, relatively slow microbial activity and permafrost at some of the sites.
With focus on the clean up of contaminated soils in the cold regions, Mike Reynolds explains that fungi and bacteria can degrade or break down many contaminants. Depending upon the variables involved, there are differing degrees of this breakdown. Some contaminants are degraded entirely to carbon dioxide and water. Other contaminants may degrade partially making them a lesser environmental problem. CRREL's soil microbiology laboratory finds way to make the degradation better.
One way to do this is by using the rhizosphere effect. The rhizosphere is the zone of increased microbial growth and activity in the soil close to plant roots. It is a root-soil relationship. Plant produce excess carbon compounds by photosynthesis and exude these through their roots, where the compounds stimulate soil microbial growth near the root surfaces. This in turn stimulates bioremediation, the break down of contaminants in the soil.
Plants such as annual ryegrass and red fescue have dense, fibrous root systems with tremendous surface area and they influence a greater percentage of the soil than does a plant with a few large, thick roots. Rhizosphere augmentation is faster and more complete than natural remediation of contaminants and the benefits increase for the more challenging contaminants.
Studies initially determined that contaminant degradation tends to be faster and more complete in vegetation and nutrient treated soils. Similar results have been found for diesel and crude-oil contaminated soils. Because degradation occurs in the soil near the roots, plants do not take up significant amounts petroleum contaminants. In contrast, plants used in the bioremediation of metals in soils often function by taking up metals into the plant tissue.
In cold regions, bioremediation may take several years because of short growing seasons. Generally, soils may be bioremediated for thicknesses of up to three or four feet of contamination.
In order to measure microorganisms in the soil, cellular components first must be washed out or extracted from the soil. Mike Reynolds and his colleagues then look at the soil extractions; quantify the cellular components, and estimate microorganism abundance and composition.
In order to promote microbial growth in the soil, the soil is evaluated for what needs to be added or altered. Soil moisture or temperature, for example, may be altered to encourage microbial activity. Readings of carbon dioxide are used as an indicator of growth of microbes. The respirometer, an instrument for measuring carbon dioxide given off by microbes in the soil, is used for conducting these assessments.
One of the greatest challenges is to determine what is happening to the soil from the chemist's point of view. David Ringelberg interfaces microbiology with organic chemistry and uses a variety of techniques to look at the soil. For instance, he may recover lipids or DNA to conduct observations for microorganisms.
For further information and contact information investigate Mike Reynold's CRREL web page at: http://www.crrel.usace.army.mil/es/personnel/reynolds.charles.html. To explore the Soil Microbiology Lab and the Chemistry Lab at CRREL go to http://www.crrel.usace.army.mil/welcome/facilities/crrel_facilities.html.
By Sandra Kolb, March 2001
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