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United States Department of Agriculture

Agricultural Research Service

Title: Monitoring and Modeling Lateral Transport Through a Large in Situ Chamber

Authors
item Starr, James
item SADEGHI, ALI
item PACHEPSKY, YAKOV

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2005
Publication Date: December 1, 2005
Citation: Starr, J.L., Sadeghi, A.M., Pachepsky, Y. 2005. Monitoring and modeing lateral transport through a large in situ chamber. Soil Science Society of America Journal. 69:1871-1880.

Interpretive Summary: Riparian/wetland areas often function as buffers for controlling nutrient and sediment transport from upland agricultural activities to adjacent water bodies. Field monitoring studies have shown that these areas can often remove nutrients and sediments moving to and through riparian zones, but the mechanisms involved in retarding and altering subsurface nutrients are not clearly understood. This study presented the design installation and experimental results of a large open-ended chamber that allows quantitative lateral flow examinations of water and solute fluxes through an isolated section of a soil profile within a riparian area. The prime characteristic of this design is the ability to control solute pulse application and maintaining water-table height at desired depth during the simulation of actual field scenarios. Results from lateral flow studies through the chamber, along with the aid of a computer simulation model(HYDRUS2D) enabled quantitative examinations of both reaction and transport parameters in and through this isolated section of soil profile within the actual domain of a riparian area. This work will be useful to scientists, regulators, and policy makers concerned with the effectiveness of riparian areas to mitigate agricultural pollutants.

Technical Abstract: Lateral flow within riparian systems has been shown to be a dominant mechanism in nutrient NO3 transport and loadings into adjacent streams. Accurate characterization of this transport component is an important step toward a more quantitative assessment of the fate and transport of nutrients and the functionality of riparian/wetland systems. An open-ended stainless steel chamber (SSC) with 0.9 x 0.9 x 1.2 m dimensions was installed over an undisturbed block of soil near a first-order stream. After establishing constant water flow, Br and NO3 tracer movement was monitored at the SSC outlet via a 10- by 10-cm grid of inlet/outlet ports. HYDRUS-2D was used to simulate flow and transport of Br and NO3 and to evaluate the applicability of the two-dimensional model to three-dimensional flow and transport that took place in the actual experiment. Advective-dispersive model and mobile-immobile zone model options were tested using the Br data. The mobile-immobile zone model provided better fit to the data indicating the presence of dual porosity in the first two soil layers. Attempts to simulate the NO3 transport in the system were not as successful, since a constant value for the denitrification rate was not applicable for the whole experiment.

Last Modified: 7/28/2014