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Monitoring and modeling lateral transport through a large in situ chamber

Starr, J.L., Sadeghi, A.M., Pachepsky, Y.A.
Soil Science Society of America journal 2005 v.69 no.6 pp. 1871
soil transport processes, nitrates, nitrate nitrogen, bromine, labeling techniques, riparian areas, wetland soils, sandy loam soils, clay loam soils, soil solution, soil hydraulic properties, denitrification, simulation models, equipment design
Accurate characterization of lateral transport components is an important step toward a more quantitative assessment of the fate and transport of nutrients and the functionality of riparian/wetland systems. Our specific objectives were: (i) to design an in situ chamber for studying lateral flow under shallow watertable and riparian zone conditions; (ii) to monitor predominantly horizontal transport of non-conservative (NO3) and conservative (Br) tracers in shallow saturated zone of the soil monolith; and (iii) to obtain reaction and transport parameters, and additional insights about the flow and transport inside the soil monolith. HYDRUS-2D model was used to simulate flow and transport of Br and NO3, and to evaluate the applicability of this model to the observed flow and transport. Advective-dispersive equation (ADE) and mobile-immobile zone model (MIM) options were tested using the Br data. The breakthrough curves (BTCs) of NO3 and Br were similar while the concentrations rose, then became distinctly different with NO3 concentrations decreasing much faster. The calibrated denitrification rate of 0.713 +/- 0.211 d(-1) was about an order and a half of magnitude larger in the loam layer (25-35 cm) than in the overlaying sandy loam layer (0-25 cm) and in the sandy clay loam layer (35-65 cm) below. Up to 60% of the introduced NO3 was lost to denitrification. The methodology presented here allowed the in situ estimation reaction and transport needed for modeling; and it showed a potential to provide detailed information critical for the interpretation of the modeling outcomes performed at field and watershed levels.