Date of Award

January 2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Engineering

First Advisor

Taufique Mahmood

Abstract

This study investigates pesticide occurrence and distribution in the Mauvais Coulee Basin, a cold-region agricultural watershed in North Dakota, over three hydrologically distinct years. Initially focusing on neonicotinoids, the scope expanded to include herbicides, fungicides, and their metabolites. We hypothesized that pesticide concentrations are significantly influenced by hydroclimatic factors—particularly snowmelt and precipitation events—as well as by application timing and land use. In wetter years, dilution effects were expected to reduce pesticide concentrations, whereas drier years result in elevated levels due to lower water volumes. Results indicated limited neonicotinoid detection, primarily due to soil characteristics such as high clay content, organic matter, and cation exchange capacity, combined with the timing of pesticide applications. Conversely, Pyrasulfotole, Metolachlor ESA, 2,4-D, and Tebuconazole exhibited notable seasonal spikes influenced by soil adsorption and runoff events. Compared to studies in regions with sandy soils and shallow aquifers, neonicotinoid mobility in this basin was more limited due to higher clay content, deeper groundwater, and the presence of two to three clay horizons in observation wells. These conditions enhanced physicochemical interactions, particularly sorption to clay and soil organic matter, which provided binding sites that reduced pesticide transport through the vadose zone. These findings underscore the crucial role of soil properties and hydrological timing in pesticide transport, as well as the importance of continuous monitoring and adaptive environmental management strategies within cold-region watersheds. Ultimately, understanding these region-specific interactions provides fundamental guidance for protecting water quality and informing agricultural management policies in cold-climate agroecosystems under changing climatic conditions.

Available for download on Saturday, June 05, 2027

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