Potential for Linking Saturated Hydraulic Conductivity and Quantitative Characterization of Soil Architecture at NEON Field Sites.

Soil architecture—the arrangement of soil peds and the pore spaces between them—is a controlling factor for many ecohydrological and environmental processes. National Ecological Observatory Network (NEON) sites, however, currently only characterize soil architecture from qualitative descriptions and, thus, do not quantitatively measure or describe soil structure or pore networks. In this study, we applied field-based multistripe laser triangulation (MLT), a recently-developed, quantitative, structured-light scanning technique, to a soil excavation wall in northeastern Kansas.  Areas of missing data were produced where the scanner could not detect the laser stripes as they swept across the surface of interest.  These surface scan gaps (SSGs) present in the resulting data outline soil structural units and allow the soil architecture to be quantified. The goal of our work was to examine relationships between these MLT-derived metrics of soil structure and saturated hydraulic conductivity (K_s) obtained by optimizing hydraulic properties to water content data measured within a soil lysimeter adjacent to an Ameriflux eddy covariance station. The optimization was conducted using a Markov chain Monte Carlo technique in combination with HYDRUS-1D. Water content was measured at 6 depths at a frequency of 30 minutes using time domain reflectometry sensors. Optimized K_s values ranged between 3548 cm d^-1 near the surface and approximately 1 cm d^-1 and were strongly correlated to the effective pore area orthogonal to the presumed direction of flow. The effective pore area was determined as the square of the geometric mean of the pore widths measured by MLT modified by the coefficient of linear extensibility (COLE). COLE allows the pore widths determined from a dry excavation wall to be approximated to widths as saturated conditions. We propose there is a need for a similar approach at NEON field sites in order to inform and enhance modeling of ecohydrological and land-atmospheric processes.