Semester

Summer

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Forest Resource Management

Committee Chair

Jason Hubbart

Committee Co-Chair

James Anderson

Committee Member

James Anderson

Committee Member

Charles Shobe

Committee Member

Michael Strager

Abstract

The paucity of research on accurate predictions of saturated hydraulic conductivity (Ksat), spatiotemporal analysis of nutrient concentrations relative to water source types (stream and shallow groundwater (SGW)), water flow directions, and land use in riparian wetlands of Appalachian mixed land use catchments underscored the need for this study. Additionally, the lack of SGW flow simulations and stream-SGW interactions using three-dimensional (3D) numerical models (i.e., MODFLOW) in these riparian wetlands further highlighted the research gap. Observed data including soil properties, Ksat, surface water (SW) and SGW levels, and nutrient concentrations, including nitrate (NO3-N), nitrite (NO2-N), ammonium (NH4-N), orthophosphate (PO43-P), total nitrogen (total_N), and total phosphorus (total_P) were collected from four stream stage monitoring sites with a total of 13 co-located piezometers during January 2020 to December 2021. Validation against observed Ksat values revealed a significant correlation of Ksat with soil texture, particularly clay content, yet underscored the low accuracy of existing pedotransfer functions (PTFs), indicating a pressing need for calibration and development of site-specific PTFs. Distinct nutrient profiles were observed between SW and SGW, with significantly higher (p < 0.05) total_N and total_P concentrations in SGW than in SW. Principal Component Analysis (PCA) and Spearman Correlation further elucidated the relationship between nutrient distributions, water source types, and adjacent land uses. Relatively stable SGW head distribution was observed with slight monthly fluctuations due to recharge rates from 3D MODFLOW simulations. The downstream reach for the study period illustrated a losing stream condition, while a monthly alternating gaining-losing stream condition was observed in the upstream area. In an experimental MT3D transport scenario including advection-dispersion and chemical reaction, lateral transport of NO3-N from SGW to the stream was observed, and NO3-N lost by denitrification surpassed NO3-N lost from SGW to stream. These studies provide valuable insights into the complexities of water and nutrient dynamics in riparian wetlands of mixed land-use catchments in the Appalachian region of the northeastern United States, offering a foundation for informed management decisions to manage these ecosystems sustainably.

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