Richard Stockton College
BUBBLES IN THE DUST: THE VESICULAR HORIZON OF DESERT SOILS
Vesicular soil horizons are a widespread feature of desert landscapes. Soils with vesicular horizons have distinct hydrologic properties and are highly sensitive to wind erosion when disturbed by human activities. Given their role in regulating the surface hydrology of desert ecosystems and their potential for hazardous dust emissions, it is wise for managers of arid lands to recognize what vesicular horizons are, where they occur, and how they respond to human activities. The horizon is named for its vesicular porosity which is formed through the entrapment of air in the silty eolian material that accumulates at the surface of many desert soils. Simply put, the horizon is made of "bubbles in dust". My research has focused on learning more about the distribution of vesicular horizons in the western United States and understanding the processes that lead to the formation of vesicular horizons. Methods utilized in this research include analysis of soil databases, the development of a field index to quantify vesicular horizon expression, and high-resolution X-ray computed tomography (CT) analysis of vesicular pore morphology. Through this research I found that there are 1,092 soil series that have a vesicular horizon in the official series description, and these soils are mapped over a total of 157,000 km2 of the western U.S. I developed a vesicular horizon index (VHI) to quantify the morphologic expression of the vesicular horizon in soils. Application of the VHI to the soil databases revealed that vesicular horizons are better expressed in the Great Basin Desert (the cold desert) compared to the Mojave and Sonoran Deserts (the hot deserts). The VHI was also utilized to study the effects of disturbance on vesicular horizons and the rate of vesicular horizon recovery following disturbance. Vesicular horizon morphology was found to show incipient development within 1-year following disturbance. The degree of development within the incipient vesicular horizons was positively correlated with the amount of precipitation that occurred during the recovery period. Studies of the pore morphology of vesicular peds using CT analysis revealed that the pores in the vesicular horizon have a far more varied geometry the typical spherical vesicles. The vesicular peds contain equant, prolate, oblate, and hemispherical vesicles, irregular vughs that are sometimes connected into large networks, and planar voids. A genetic relationship between the pore types is proposed to involve vesicles merging to form larger vughs and collapsing to form planar voids. The distribution of pores within vesicular peds suggests that the formation of porosity in the vesicular horizon occurs from the outside of the peds and proceeds inward to the center of the ped with time. Overall, these research results suggests vesicular horizons are dominant in the cold desert climate of the Great Basin, which is dry enough to be dusty, but wets up frequently, trapping more bubbles in the dust with each rain.