Submitted to: Vadose Zone Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/6/2008
Publication Date: 7/19/2009
Publication URL: http://www.ars.usda.gov/SP2UserFiles/Place/53102000/pdf_pubs/P2249.pdf
Citation: Segal, E., Shouse, P.J., Bradford, S.A. 2009. Deterministic Analysis and Upscaling of Bromide Transport in a Heterogeneous Vadose Zone. Vadose Zone Journal. 8(3):601-610. Interpretive Summary: Accurate knowledge of chemical transport processes in the root zone is needed to predict chemical transport potential in risk assessment, and in the design of remediation and management practices. In this work the transport behavior of a nonreactive chemical (bromide) in the field and laboratory was studied at different length scale, and in the presence and absence of decaying root channels. Many of the previously reported difficulties associated with modeling field scale chemical transport were overcome by the proper choice of conceptual model for solute transport, detailed measurements of soil hydraulic properties, and by analyzing the average transport data that was collected from 4 locations at the same depth and time. This information will be of use to scientists, regulators, and consultants who need to quantify and simulate transport processes in the root zone.
Technical Abstract: Conservativ solute transport experiments were conducted at a field plot and on an undisturbed soil core from the same site. The hydraulic and solute transport properties were extensively characterized so that the data could be analyzed from a deterministic perspective. To investigate the influence of scale and conceptual model on solute transport in the relatively homogeneous upper soil profile of the field site, breakthrough curves that were collected at different depths in the undisturbed column and in the field experiments were compared and analyzed. The mobile-immobile model provided a physically realistic description of the column data that was largely independent of the transport distance, and upscaling from the undisturbed core to the field plot was relatively successful. Mean and variance of the Br- travel times were controlled by plot-scale variability in soil water content and heterogeneity, which was overcome by averaging the concentration values from four locations at the same depth and time, and analyzing the Br- transport behavior as a one- dimensional process. Diff erences between the measured and simulated mass balances, average concentration, and the variations in concentration were predicted reasonably well across depth and time. Although prediction of the exact concentration information at a given point was not achieved, this study demonstrates that areaaverage Br- transport in a heterogeneous vadose zone can be deterministically quantified.