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Spatial Structure of Solute Transport Variability in an Unsaturated Field Soil
Author(s) -
Ellsworth T. R.,
Boast C. W.
Publication year - 1996
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1996.03615995006000050010x
Subject(s) - spatial variability , scale (ratio) , soil science , length scale , hydrology (agriculture) , geology , mathematics , statistics , physics , geotechnical engineering , mechanics , quantum mechanics
Abstract Three solutes were applied in series under steady, unsaturated flow to determine the spatial scale dependence of transport. Twenty‐seven days after solute application, a 2 by 2 by 2 m 3 field plot was excavated using two measurement scales, 22.2 by 22.2 by 10 cm 3 (scale L ) and 7.4 by 7.4 by 10 cm 3 (scale l ), providing two sets of 81 samples for each 0.1‐m layer to a depth of 2.0 m. For each chemical and for each scale, vertical moment analysis was performed on the data for each of the 81 vertical columns. Evidence of enhanced local horizontal mixing with increasing mean travel time was observed in two ways: (i) a decrease in mass recovery variance at scale L for NO − 3 (center of mass at 80‐cm depth) vs. Br − (46‐cm depth of center of mass), and (ii) a horizontal correlation range in solute concentrations in individual 0.1‐m‐thick layers, which was lowest between 70 and 130 cm deep. Point variograms of the vertical moments for each solute were estimated by simultaneous deconvolution of the two observed (at scales l and L ) area‐averaged variograms. Dispersion variance analysis (based on these point variograms) characterized the variability within the plot of mass recovery and center of mass depth as a function of sample size. Several approaches for characterizing plot‐ or field‐scale transport features from soil‐core scale measurements were evaluated. The horizontal dependence of the vertical variance increased with mean travel time. For each tracer, this dependence was reasonably characterized as the sum of the dispersion variance in the center of mass and the average L ‐scale vertical variance.