Title: Impact of Soil Hydraulic Properties on Groundwater-Dependent Ecosystems Across Elevations in a Semi-Arid Riparian Zone

Abstract: Soil water retention and storage capacity are fundamental to understanding water availability within an ecosystem. Both variables are influenced by soil hydraulic properties, which describe the relationship between soil texture and water holding capacity. However, measuring the water holding capacity in the field is challenging, and the spatial variability of soil moisture retention is poorly understood. Soil water retention ensures that plants have seasonal access to water in unsaturated soils, especially during periods of low precipitation. This is particularly important in water-limited systems where transpiration rates have great influence on groundwater-dependent ecosystems. In semi arid, snow dominated watersheds, the importance of transpiration in riparian zones likely varies across the rain-snow transition as water and energy limitations change from cool-wet high elevations to hot-dry low elevations. The goal of this research is to model the vertical distribution of plant water uptake across a rain-snow transition zone using soil hydraulic properties. We hypothesize that transpiration rates in deep soil profiles play a crucial role in vegetation survival during dry seasons by providing essential moisture to support plant growth in shallow soil depths within a semi-arid environment. This hypothesis will be tested by simulating soil water movement in riparian zones in low, mid, and high elevation sites with a commonly used Richards equation solver, Hydrus-1D. The model will be parameterized using field measurements of soil hydraulic properties. Soil cores were collected by investigators during the summer of 2024 from three depths at both riparian zone and hillslope sites across three distinct locations. The samples will be processed using multiple instruments to construct soil moisture curves, which will be integrated into Hydrus-1D modeling.

Advisor: James McNamara

Committee: Qifei Niu and Alejandro Flores