Masters Theses

Date of Award

8-1996

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Glenn V. Wilson

Committee Members

Mike Mullen, Larry McKay, Anthony Palumbo

Abstract

Microorganisms have been introduced into our soils and groundwater through land treatment of domestic animal waste, septic waste disposal, and municipal waste landfills. Bioremediation is a technology that greatly depends upon the movement of microorganisms through the soil for the purpose of microbial degradation of contaminants. The physical (particle size distribution, surface area, and porosity), and chemical characteristics (pH, OM, cations and anions), of a soil can significantly affect and alter bacteria fate and transport. The objectives of this study was to determine the natural physical, chemical, and microbial heterogeneity at the intermediate scale, and to evaluate the role of physical and chemical heterogeneities on microbial populations and their movement. Undisturbed soil blocks were taken from three depths within the vadose zone at a site in Oyster, Virginia. Simulated rainfall applications were made on the blocks and spatial heterogeneity in flow and transport was measured with an 8 x 8 grid of 3.75 cm square outflow collection cells. The blocks taken from the 4.5 m and 5.9 m depths, received a CaCl solution containing 400 mg L-1 phosphate to determine the mobility of phosphates and its effect on indigenous populations. The 5.9 m block, however, a fluorescent bacteria, Pseudomonas putida, was added to the rainfall solution to determine its mobility through soil. Effluent samples were analyzed for their chemistry (pH, anions, and cations) and indigenous microbial or Pseudomonas putida concentrations. Spatial variability in soil chemical properties (pH, cations, and anions), physical properties (particle size distribution, porosity, and surface area), and microbial populations were determined on 3.75 cm3 samples at 5 cm depth increments. Flow and transport of solutes was extremely heterogeneous through the 4.5 and 5.9 m blocks with only 17% and 4% of the collection cells receiving flow, respectively. Preferential flow patterns, which were more prominent in the 5.9 m block, were believed to be produced by the layering of fine sand over layers with greater amounts of coarse sand. Effluent microbial concentrations varied greatly, both spatially and temporally. The highest microbial concentrations were observed in the collection cells where the highest flow rates were observed. However, the highest variability in microbial numbers were observed in the collection cells where slower flow rates were recorded. Spatial distributions of both indigenous and Pseudomonas putida populations within the soil were found to be strongly controlled by particle size distribution. Bacteria within the areas consisting of primarily small particle sizes, such as fine sands were trapped, while regions with larger particles allowed the microbes to be readily flushed through the soil block. Soil chemistry was found to be less influential on the distributions of microbial populations, as compared to the physical properties of the soil, due to the lack of clay. Soil pH and phosphate concentrations both significantly effected microbial distributions, with the highest numbers observed in the samples with a pH < 7.0 and high phosphate concentrations. While bioremedial feasibility studies often center on soil chemistry and nutrient concentrations, our studies indicate that equal consideration should be given to the physical properties of the soil.

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