| dc.description.abstract | Soil aggregates, a fundamental unit of soil structure, are formed when minerals and organic matter bind together. Physiochemical drivers, such as soil texture and organic carbon (OC), help govern soil aggregate resiliency to changes in climate, vegetative land cover, and anthropogenic pressures. These drivers in turn shape the spacing between aggregates upon which water is stored and moved through the Earth's critical zone (CZ). Recent evidence suggests that soil structure may be changing on decadal timeframes as a result of differences in moisture conditions leading to potentially significant changes in soil hydraulic properties (e.g., saturated hydraulic conductivity, Ksat). Soil macropore geometry, determined through multistripe laser triangulation (MLT), and shrink-swell behavior, assessed through measures of the coefficient of linear extensibility (COLE), can be related to Ksat to predict how future climatic and land use conditions will influence soil water stores and fluxes. Additionally, findings from this study can be related to more qualitative, field descriptions such as horizon thickness and soil structural classification. In this research we used precipitation (580-1012 mm; semiarid-to-mesic at Hays, Konza, and Welda) and land use (Native, Post-Agriculture, and Agriculture) gradients across Kansas to quantitatively explore these relationships. To characterize the influence of climate/land cover-induced changes on pore geometry and hydraulic properties in shrink-swell soils and relate these measures to soil moisture, we collected soil monoliths from the face of ~ 2 m deep soil pits located under three land use types with three differing precipitation regimes, and installed soil moisture sensors at three depths (10, 40, and 120 cm). Key results from this work showed that: 1) pore aspect ratio and the tortuosity coefficient generally increased with depth, especially at Native sites, 2) pore density (Dssg) at depth was greatest at drier sites (Hays) compared to wetter sites (Konza and Welda), and 3) the effective pore area (Aeff) increased with decreasing mean annual precipitation (MAP), which was concurrent with lower COLE, clay, and OC contents, but little change in pore width (min Feret diameter when measured at a dry state). Land use, particularly at row-crop Agricultural sites, alters the nature of these relationships. For example, mean aspect ratio and tortuosity coefficients were higher at Agricultural than Native land uses for both the near surface and subsurface horizons. We can infer that the observed decline in Aeff with increased MAP at our sites results in a decline in Ksat, as previously reported work showed a positive relationship between Ksat and Aeff. Soils scanned through MLT can provide more detailed, quantitative-based metrics that can improve estimates of hydrologic fluxes. | |
