Monday, 7 November 2005
9

An Instrumented Soil Column for Teaching Unsaturated Flow and Transport Processes.

J. Mark Blonquist Jr., Robert Heinse, Pakorn Ditthakit, R. William Mace, and Scott B. Jones. Utah State University, 4820 Old Main Hill, Logan, UT 84322-4820

An instrumented soil column for educational and scientific purposes was designed and constructed to assist in teaching and research of subsurface transport processes in soils (e.g., carbon sequestration, solutes). The processes of root and microbial respiration lead to a build-up of carbon dioxide in the subsurface, which drives carbon fluxes leaving the soil surface. These fluxes are highly dependent on soil moisture, which also influences the transport of solutes and contaminants into the subsurface. Our objectives were to develop a teaching tool to measure and observe gas, liquid and solute fluxes in a controlled laboratory soil column. The soil column was packed with Millville Silt Loam soil to a uniform density. Water content was partially controlled by infiltration rate at the top of the column and by controlling the suction of a ceramic cup drain at the bottom (60 cm below the surface). A variety of sensors were installed at various heights in the column. Temporal patterns of soil water content, matric potential, gas concentrations and temperature were measured by time domain reflectometry (TDR), tensiometers, CO2 and O2 sensors, and thermocouples, respectively. Water content measurements were used to derive gas diffusion coefficients followed by application of Fick's law from gas concentration measurements for CO2 flux determination. TDR measurements can be further used to derive the bulk electrical conductivity of the soil, which is used to observe and model solute transport through the soil column. A column with a minimum configuration of sensors can be constructed for around $1000.

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