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University of Kentucky (2020)

ISOTOPIC AND GEOCHEMICAL TRACERS OF GROUNDWATER FLOW IN THE SHIVWITS PLATEAU, GRAND CANYON NATIONAL PARK

Wilson, Jonathan W.,

Titre : ISOTOPIC AND GEOCHEMICAL TRACERS OF GROUNDWATER FLOW IN THE SHIVWITS PLATEAU, GRAND CANYON NATIONAL PARK

Auteur : Wilson, Jonathan W.,

Université de soutenance : University of Kentucky

Grade : Master of Science (MS) 2020

Résumé
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 transition

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