DOI

10.17077/etd.bhih2w3g

Document Type

Thesis

Date of Degree

Spring 2017

Degree Name

MS (Master of Science)

Degree In

Geoscience

First Advisor

Jeff A. Dorale

First Committee Member

Elmer A Bettis

Second Committee Member

Keith Schilling

Abstract

The stable isotopic composition of groundwater within a watershed in eastern Iowa was studied in order to understand how water moves through the system. Samples were gathered using multiple observation wells and pore water samplers and then analyzed to determine the δ18O and δ2H of each sample. Shallow pore water is much more variable in its isotopic composition than deeper water and seems to be more greatly affected by evapotranspiration, whereas groundwater below the water table appears to show a stable isotopic signature suggesting the integration of multiple rain events. Other samples of similar depths across the slope of a hill were also used to observe differences across the area. By observing changes over time in the signatures of these samples, it can be seen that the crest of the hill is most greatly influenced by infiltration from precipitation while the side of the hill is influenced more by throughflow. By combining stable isotope analyses, knowledge of the medium through which the water is moving and the general mechanics of a watershed, a more advanced understanding of how water interacts with and moves through the ground can be gained.

Public Abstract

Groundwater from multiple depths and locations were collected over a six-month period within a watershed at the headwaters of Clear Creek in eastern Iowa. Those samples were analyzed to obtain oxygen and hydrogen isotope information, which can be used to better understand the movement of water through the system. By observing the trends and changes in oxygen isotopes at different depths and locations over time, inferences can be made about the sources and interactions that affect those different samples. In general, it appears that shallow water is heavily influenced by evapotranspiration (ET) as well as individual precipitation, showing an enriched signal during the growing season as a result of ET that becomes depleted as it drops off in the winter months. While individual precipitation events can vary greatly, they are all integrated into the deeper groundwater meaning that this deeper water shows a much more stable signature that appears to represent the average signal of all precipitation events. By combining these inferences with a knowledge of mechanics of the watershed system and the medium through which the water is moving, a deeper understanding of the entire system can be gained.

Keywords

Groundwater, Hydrology, Pore Water, Stable Isotopes

Pages

vii, 44 pages

Bibliography

Includes bibliographical references (pages 39-44).

Copyright

Copyright © 2017 Jake Bucklin

Included in

Geology Commons

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