Author ORCID Identifier

https://orcid.org/0000-0002-2341-8886

Year of Publication

2020

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Arts and Sciences

Department/School/Program

Earth and Environmental Sciences (Geology)

First Advisor

Dr. Andrea M. Erhardt

Second Advisor

Dr. Benjamin Tobin

Abstract

As the impacts of global climate change on water resources continue to become more apparent, proper understanding and management of groundwater resources will be needed as supplies become more strained. Traditional methods of characterizing groundwater systems are time-intensive, costly, and can be difficult to complete in remote areas. Using ambient geochemical tracers from discrete sampling could aid in characterizing spring systems through determining flow paths, recharge areas, and carbon cycling. However, using discrete seasonal samples to understand the hydrogeology of complex, mixed-lithology aquifers has not been extensively examined. Here we explore using δ13C of dissolved organic carbon (DOC), δ13C of dissolved inorganic carbon (DIC) and fluorescent dissolved organic matter (fDOM), together with water isotopes, major ions, and geochemical modeling, to characterize springs of the Shivwits Plateau in Grand Canyon National Park. Values of carbon isotopes and fDOM for all springs reflect source values for regional surface vegetation and heterotrophic degradation of terrestrial DOM. Principal component analyses show that springs can be grouped into four groups by geochemical variability: 1) a shallow epikarst system, 2) a flow path through gypsiferous beds of the Toroweap Formation on the eastern side of the plateau, 3) a short, canyon slope runoff-dominated flow path through the Supai Group, and 4) a deeper complex flow system in the Redwall Limestone with characteristics of all other flow systems, which indicates mixing. Results show that the methods used can provide a simple conceptual model of a complex groundwater system, but higher–resolution spatial and temporal data are needed to fully understand changes resulting from changing climate. As appropriations from the Colorado River already exceed its annual streamflow and the regional climate is predicted to become more arid, characterizing groundwater resources for water supply will be paramount for the region as well as in other areas that will experience similar transitions.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.488

Funding Information

This study was supported by funding from the National Park Service in 2019 and 2020, the Geological Society of America's John W. Hess Research Grant in 2019, and travel funds from the Department of Earth and Environmental Sciences in 2019.

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