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DIVISION S-1—SOIL PHYSICS

Influence of Initial and Boundary Conditions on Solute Transport through Undisturbed Soil Columns

^a Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, 960 Carling Ave., Ottawa, ON, Canada, K1A 0C6
^b 3-7 University Hall, Univ. of Alberta, Edmonton, AB, Canada, T6G 2J9

^* Corresponding author (gary.kachanoski{at}ualberta.ca).

The effect of initial soil water content () and steady and transient water flow boundary conditions (J_w) on the transport of identical solute pulses was examined in four undisturbed soil columns. Solute breakthrough curves (BTCs) and were monitored nondestructively using time domain reflectometry (TDR). Pulse concentrations were predicted from TDR impedances () using either a steady J_w calibration or a transient J_w calibration. The steady J_w calibration, ß_s, was estimated from the steady J_w BTC. The transient calibration, ß(), was estimated from the changes in ^–1() between three different calibrating solutions of Cl^– (1.106, 1.503, and 1.900 g L^–1) in the pore space. All ß() curves had a very similar decreasing curvilinear shape. At one location the ß() curve was high and residual water was not completely replaced by the calibrating solutions. The steady J_w calibration values were generally slightly lower than the equivalent ß() value, but collectively they followed a similar decreasing curvilinear trend with steady _s. Solute applied to initially dry soil tended to lead the transient J_w wetting front and breakthrough began with the start of cumulative drainage. These BTCs also had the greatest amount of BTC tailing. Solute applied to initially wet soil had less BTC tailing. The least amount of BTC spreading occurred during the steady J_w condition. The two transient J_w experiments had very similar distributions of solute with depth, despite the contrasting initial conditions. The pores actively transporting solute appear to be determined by the J_w boundary condition.

Abbreviations: BTC, breakthrough curve • EC, electrical conductivity • J_w, water flux • MPA, mass per unit area • pdf, probability density function • RPM, revolutions per minute • subscript [s], steady • TDR, time domain reflectometry • , water content • , soil water potential