- Restrictions on Access:
- Open Access.
- Subsurface restrictive layers play a crucial role in surface runoff and lateral flow processes; however, only coarse maps (scale 1: 1:12,000 - 1:63,360) are currently available through SSURGO (Soil Survey Geographic Database) portraying their depth and distribution in the landscape. High-resolution information on soil restrictive layers is urgently needed for use in hydrologic modeling and land management planning. In this dissertation, I investigate the types and distribution of soil restrictive layers and evaluate three different methods for obtaining high-resolution datasets of soil restrictive layers, including i.) the use of soil morphological features: fragic properties or fragipans (Bx horizons) and low chroma ( 2) depletions (LCDs) in soil cores, ii.) ground penetrating radar (GPR), and iii.) electromagnetic induction (EMI). I relate morphological indications of restriction (i.e. LCDs) to measurements of saturated hydraulic conductivity (Ksat) from borehole permeameter measurements and water table levels from shallow wells monitored over 2.5 years. I use particle size analysis to investigate the presence of a lithologic discontinuity observed during soil morphological observations. I use logistic regression and correlation to determine significant relationships between restrictive layer presence/absence and depth (determined using the three methods) and LIDAR-derived topographic variables. Topographic variables investigated include: aspect, slope, planform curvature, profile curvature, total curvature, topographic wetness index, specific contributing area, and topographic position index. The logistic regression models were evaluated based on known soil information from well-studied watersheds in the Ridge and Valley Province of Pennsylvania, wet boot mapping of saturated regions, cross-validation, a validation dataset of 112 soil cores, and comparisons to SSURGO. I found that soils containing LCDs had significantly (p = 0.003) lower Ksat (mean Ksat = 0.018 cm hr-1) than those without LCDs (mean Ksat = 2.8 cm hr-1) and that soils with LCDs had active, shallow water tables during 2.5 years of water table monitoring. I found that 87% and 27% of soil cores that were described as having fragic properties had a lithologic discontinuity at or above the Bx horizon (for FD-36 and Mattern watersheds, respectively). Particle size analysis confirmed the presence of a lithologic discontinuity; clay-free silt percent was significantly (p < 0.05) greater above the lithologic discontinuity, and rock fragment volume percent and clay-free sand percent were significantly greater (p < 0.05) below the discontinuity. Correlations between depth to Bx/LCDs and individual topographic variables (for the FD-36 and Mattern combined dataset) were very low (
- Dissertation Note:
- Ph.D. Pennsylvania State University 2018.
- Technical Details:
- The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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