Effect of velocity and water content on the gas-phase partitioning tracer test for the in-situ measurement of soil-water content in a large weighing lysimeter

Abstract

This thesis describes research conducted to evaluate the efficacy of the gas-phase partitioning tracer method for measuring bulk soil-water content. A series of tracer experiments were conducted at two velocities and water contents in a well instrumented weighing lysimeter. The method is based on introducing gas-phase conservative and water-partitioning tracers into the system. The partitioning tracer dissolves into the water, which retards its movement with respect to a non-partitioning tracer. This retardation is a function of the soil-water content. The soil-water contents estimated from comparative moment analyses of the measured breakthrough curves were compared to values obtained using traditional methods for determining soil-water content. These methods include: neutron thermalization, time domain reflectometry, gravimetric core analysis, and soil tension. The results from the tracer test compare favorably at different velocities and soil-water contents with the data provided by traditional methods. For the slower velocities, the tracer results yielded soil-water contents of 0.06 and 0.12 while the traditional methods 'indicated soil-water contents of 0.06 and 0.15. Tracer tests conducted at higher velocities yielded soil-water contents of 0.05 and 0.11 while traditional methods indicated soil-water contents of 0.06 and 0.15. This indicates that the water partitioning tracer method has potential to provide accurate results under a variety of conditions.