Author
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Gish, Timothy |
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KUNG, K-J - UNIVERSITY OF WI |
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Submitted to: Geoderma
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/22/2006 Publication Date: 6/22/2006 Citation: Gish, T.J., Kung, K-J., S. 2006. A protocol for quantifying shallow groundwater leachate fluxes in a non-tile drained system. Geoderma. 138:57-64. Interpretive Summary: The inability to simultaneously quantify water flow rates through soil and their chemical composition has severely limited our knowledge of chemical transport theory. Water flow rates through soil are very complex and exhibit a tremendous amount of spatial variability, thus most studies simply sample chemical concentrations and assume a specific water flow process. Recently a protocol was developed for tile-drained systems that monitored both the water flow rates and the chemical composition of the moving water. This protocol was extended to a non-tile drained soil system with a perched or shallow water table. Three mobile tracers were applied with this protocol and mass recoveries demonstrated that over 97% of all three surface applied chemicals were successfully monitored. This protocol will help scientist involved with water quality investigations to better understand the flow processes governing chemical transport to groundwater, and will lead to improved water quality models. Technical Abstract: A total solute flux monitoring protocol recently developed for tile-drained systems was extended to a coarse loamy sand soil with a perched water table located at 1.68 m. Three mobile tracers were applied to a 28.2 m2 area around an observation well at different times to quantify chemical transport. The first tracer, bromide (1,64kg Br ha-1) was surface broadcast applied around the observation well two days before the irrigation at 4.1 mm/h was initiated. The second tracer, chloride (518 kg CL ha-1) was surface broadcast immediately before irrigation was initiated, while the third tracer pentafluorobenzoic acid (167 kg PFBA ha-1) was applied 7 hr after irrigation began. The water table height in observation well was kept constant by pumping water out of the well from the water table interface, while the water table height below the well pumping depth (1.68 m) was continuously monitored. The soil water content profile for the top 1.8 m were also continuously monitored with a moisture capacitance probe (MCP). Flux results from the study show that: 1) this protocol successfully recovered over 97 percent of all three surface applied tracers; 2) at 4.1 mm h-1 over half of the surface-applied tracers were recovered at a depth of 1.68 m after only 280 mm of irrigation; 3) by the time piston flow theory predicted the front would reach the 1.68 m depth, 80% of the applied tracers had already leached through the soil profile, and 4) at this location, the solute fluxes were dominated by preferential flow when subjected to a 4.1 mm h-1 irrigation rate. These preliminary results suggest this protocol may be a useful tool for quantifying a total solute transport flux in non tile-drained soils with a shallow or perched water table. |
