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Title: THE LIMITED ENTRAPMENT MODEL TO SIMULATE THE BREAKTHROUGH OF ARTHROBACTER AND AQUASPIRILLUM IN SOIL COLUMNS

Author
item Pachepsky, Yakov
item DEVIN, BORIS - MOSCOW STATE U., RUSSIA
item POLYANSKAYA, LIUBOV - MOSCOW STATE U., RUSSIA
item Shelton, Daniel
item SHEIN, EUGENY - MOSCOW STATE U., RUSSIA
item GUBER, ANDREY - U. OF CA, RIVERSIDE, CA

Submitted to: International Agrophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2006
Publication Date: 10/1/2006
Citation: Pachepsky, Y.A., Devin, B.A., Polyanskaya, L.M., Shelton, D.R., Shein, E.V., Guber, A.K. 2006. The limited entrapment model to simulate the breakthrough of arthrobacter and aquaspirillum in soil columns. International Agrophysics. 20(3):207-218.

Interpretive Summary: Bacterial transport through soils is attracting more attention because soil serves as an environmental bacterial filter, thereby reducing microbial contamination of ground water. Although it is generally known that bacteria can stick together and form clusters, little is known about how cluster formation impacts bacterial transport through soil. We conducted a series of transport experiments, using two different bacteria, with the objectives of developing an adequate model to simulate bacterial transport and to improve our understanding of the effect of cluster formation on transport. Pulses of bacteria suspension were applied to the top of soil columns followed by the application of sterile water. The concentration of bacteria in the effluent and distribution of bacteria in the soil were determined. The effluent bacterial concentrations were occasionally larger than influent concentrations indicative of cluster formation. Photographs of soil-bacteria specimens showed the presence of clusters where the bacteria were trapped in soil pores. More clusters were found in the lower section of soil columns compared with the upper section. We developed the "limited entrapment model" to simulate the observed bacterial transport. The model was able to simulate the observed transport uncer assumptions that (a) the capacity of soil pore space to trap bacteria is limited, (b) bacteria entrapment accelerates as the amount of trapped bacteria approaches the soil trapping capacity, and (c) the trapped bacteria form cell clusters that may be released back to the soil solution but travel short distances before being re-trapped because of their size. Cell cluster formation may be a significant factor affecting bacterial transport through soil.

Technical Abstract: Bacterial transport through soils is attracting more attention because soil serves as an environmental bacterial filter, thereby reducing microbial contamination of ground water. We conducted a series of transport experiments, using Aquaspirillum and Arthrobacter, with the objectives of developing an adequate model to simulate bacterial transport and to improve our understanding of the mechanisms controlling bacteria transport through soils. Disturbed samples from an Alfisol topsoil and subsoil were used to fill 15-cm long soil columns. A pulse of bacterial suspension (initial concentration of 1011 cells mL-1) was applied to the top of each soil column followed by the application of sterile water. Bacteria were counted in effluent portions and in soil using microscopy. Large variations were observed in the shape of breakthrough curves; effluent bacterial concentrations were occasionally larger than influent concentrations. We developed the "limited entrapment model" to simulate the observed bacterial transport. The model assumes that (a) the capacity of soil pore space to trap bacteria is limited, (b) the bacteria entrapment rate depends on the amount of trapped bacteria and that the entrapment accelerates as the amount of trapped bacteria approaches the soil trapping capacity, and (c) the trapped bacteria form cell clusters that may be released back to the soil solution but travel slowly and may become re-trapped because of their size. The new model provided a satisfactory fit to data and underscored the importance of cell cluster formation for bacterial transport through soil.