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WATER RESOURCES RESEARCH, VOL. 42, W10405, doi:10.1029/2005WR004550, 2006

Impact of microbial growth on water flow and solute transport in unsaturated porous media

R. R. Yarwood

Department of Crop and Soil Science, Oregon State University, Corvallis, Oregon, USA


M. L. Rockhold

Pacific Northwest National Laboratory, Richland, Washington, USA


M. R. Niemet

CH2M Hill, Corvallis, Oregon, USA


J. S. Selker

Department of Bioengineering, Oregon State University, Corvallis, Oregon, USA


P. J. Bottomley

Department of Crop and Soil Science, Oregon State University, Corvallis, Oregon, USA
Department of Microbiology, Oregon State University, Corvallis, Oregon, USA


Abstract

A novel analytical method was developed that permitted real-time, noninvasive measurements of microbial growth and associated changes in hydrodynamic properties in porous media under unsaturated flowing conditions. Salicylate-induced, lux gene-based bioluminescence was used to quantify the temporal and spatial development of colonization over a 7-day time course. Water contents were determined daily by measuring light transmission through the system. Hydraulic flow paths were determined daily by pulsing a bromophenol blue dye solution through the colonized region of the sand. Bacterial growth and accumulation had a significant impact on the hydraulic properties of the porous media. Microbial colonization caused localized drying within the colonized zone, with decreases in saturation approaching 50% of antecedent values, and a 25% lowering of the capillary fringe height. Flow was retarded within the colonized zone and diverted around it concurrent with the expansion of the colonized zone between days 3 and 6. The location of horizontal dispersion corresponded with the cell densities of 1–3 × 109 cells g−1 dry sand. The apparent solute velocity through the colonized region was reduced from 0.41 cm min−1 (R2 = 0.99) to 0.25 cm min−1 (R2 = 0.99) by the sixth day of the experiment, associated with population densities that would occupy approximately 7% of the available pore space within the colonized region. Changes in the extent of colonization occurred over the course of the experiment, including upward migration against flow. The distribution of cells was not determined by water flow alone, but rather by a dynamic interaction between water flow and microbial growth. This experimental system provides rich data sets for the testing of conceptualizations expressed through numerical modeling.

Received 6 September 2005; accepted 14 July 2006; published 5 October 2006.

Keywords: bacteria in porous media; bacteria in the subsurface; vadose zone.

Index Terms: 0498 Biogeosciences: General or miscellaneous; 1865 Hydrology: Soils (0486); 1875 Hydrology: Vadose zone; 1895 Hydrology: Instruments and techniques: monitoring.

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Citation: Yarwood, R. R., M. L. Rockhold, M. R. Niemet, J. S. Selker, and P. J. Bottomley (2006), Impact of microbial growth on water flow and solute transport in unsaturated porous media, Water Resour. Res., 42, W10405, doi:10.1029/2005WR004550.