Wednesday, November 7, 2007
285-4
Equilibrium and Physical Non-Equilibrium Solute Transport through Surface and Subsurface Undisturbed Soil Columns.
Francisco Bedmar, Department of Plant Production, Soil and Machinery, University of Mar del Plata, Ruta Nacional 226, km 73.5, Balcarce, Argentina, José Luis Costa, Department of Agronomy, EEA-INTA Balcarce, Ruta Nacional 226, km 73.5, Balcarce, Argentina, and Daniel Giménez, Department of Environmental Sciences, Rutgers, The State University of New Jersey, 14 College Farm Road, New Brunswick, NJ 08901-8551.
The objectives of this work were 1) to study the influence of surface and subsurface horizons of two soils on solute transport through undisturbed soil columns, 2) how physical properties are related to transport parameters, and 3) to determine if convection-dispersion equation (CDE) under equilibrium (CDEeq) or non equilibrium (CDEneq) approach adjust better. Undisturbed soil cores were collected from A, B and C horizons of two soils under no tillage system, from General Alvarado (GA) and Tres Arroyos (TA) locations (Buenos Aires Province, Argentina). Displacement studies were carried out with Bromide as a non-reactive tracer. Data were quantitatively evaluated by mean of the computer program CXTFIT version 2.1 to estimate transport parameters velocity (v) and hydrodynamic dispersion (D). The CDE was used including the deterministic models of transport CDEeq and CDEneq. Although shape of some BTCs of horizons A and B of soils showed tailing, asymmetry and early appearance of the tracer, that could lead to suspect the presence of non equilibrium process of transport, there was no statistical difference between the goodness-of-fit of the CDEeq and CDEneq models between fitted and observed BTCs, confirming that both models had acceptable fits. Variations in v and D parameters across the horizons indicated that the leaching patterns in both soils were not spatially uniform. Variations mainly in structure governed transport in soil horizons A, B, whereas structure and texture dominated the process in the C horizon. In general, v and D of bromide were higher in the upper horizons, that could have implications for groundwater quality since, early in the leaching process, more solute will be found deeper in the soil profile.