Graduate Defense: Zahra Ghahremani

Thesis Information

Title: Use Of Geochemical And Machine Learning Techniques To Examine Soil Inorganic Carbon Provenance And Distribution In A Cold Desert Ecosystem

Program: Master of Science in Hydrologic Sciences

Advisor: Dr. Jen Pierce, Geosciences

Committee Members: Dr. David Huber, Geosciences; and Dr. Linda Reynard, Geosciences

Abstract

The importance of dust deposition in the biogeochemical cycling of nutrients, and soil formation in Critical Zone is well-known. Anthropogenic activities such as changing land use and agricultural practices can influence dust flux deposition rates, dust organic matter content, and the chemical composition of dust. This study examines the influence of agricultural activities on aeolian deposition in two different land uses in a cold desert. We investigate seasonal and spatial variations in dust deposition rates, dust organic matter, and dust geochemistry from passive dust traps. Reynolds Creek Experimental Watershed (RCEW; Owyhee Mountains, Idaho) and the Northwest Irrigation and Soils Research Lab (Snake River Plain, Idaho) are considered non-irrigated (native) and irrigated (heavily managed) sites respectively. Our results show high variability in monthly and annual dust flux. Notably, the annual dust flux rate at the irrigated site (50.2 g/m2/year) is 7.6 times higher than the annual dust flux rate at the native site (6.6 g/m2/year). We compare measured loess accumulation rate with loess accumulation on millennial timescales inferred from loess thickness and loess ages from Optically Stimulated Luminescence (OSL). Dust accumulation rates for soils in the Snake River Plain vary from 3 to 5 cm ka-1. The OSL age from this site (50.14 ± 9.19 Ka), however, indicates that the accumulation rate ranges from 7 to 10 cm ka-1. Dust organic matter analysis indicates a relatively high percentage of organic matter in dust. While aeolian deposits in both irrigated and non-irrigated areas show organic matter content of around 18 g/m²/year (~26%) and 4 g/m²/year (~38%), respectively, the soil in both locations exhibits a low organic matter percentage of 1.3% and 1.8%, respectively. Our geochemistry analysis shows the concentration of most elements is generally lower than the average upper continental crust concentration in different seasons and land uses. Dust deposition is enriched in some trace elements such as Co, Cd, and Zn at irrigated and non-irrigated sites.