Investigating Ground and Surface Water in the Republican River Basin of Nebraska Using Water Chemistry and Environmental Isotopes

Authors

Jennifer J. Schellpeper, University of Nebraska-Lincoln

First Advisor

F. Edwin Harvey

Committee Members

David Gosselin, Dean Eisenhauer

Date of this Version

12-1999

Document Type

Thesis

Citation

A thesis presented to the Faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Natural Resource Sciences

Under the supervision of Professor F. Edwin Harvey

Lincoln, Nebraska, December 1999

Comments

Copyright 1999, Jennifer J. Schellpeper. Used by permission

Abstract

Recent legal battles concerning water use initiated an investigation of the stream/aquifer relationships in the Republican River Basin located in southwest Nebraska. Ground and surface water was analyzed for tritium, deuterium, ¹⁸O, and major ions. Temperature, pH, conductivity and alkalinity were determined on-site. Samples were collected during 1997 and 1998 from irrigation wells throughout the entire basin. Localized interactions between groundwater and surface water were examined during twenty-four hour pump tests performed on the irrigation wells screened in the alluvium along the river valley and its tributaries. These data show there are differences between the ground and surface waters from the main stem of the river and the tributaries.

Tributary groundwaters and have ¹⁸O values ranging from -10.6 to -9.0 ‰. Main stem groundwater values range from -8.5 to -6.2 ‰. Surface water values for the tributaries and main stem wells overlap, reflecting localized influence from dams. Tributary values range from -9.9 to -6.6 ‰, and main stem values from -8.9 to -5.4 ‰. Generally, main stem ground and surface waters have enriched ¹⁸O values and plot below the Global Meteoric Water Line (GMWL), while tributary waters have more depleted ¹⁸O values, and plot on the GMWL.

Main stem groundwater has an evaporative signature, shown by the ¹⁸O and 2H data. There are several possibilities for this enrichment, I) surface and groundwater irrigation, 2) reservoir leakage, 3) canal leakage, 4) a natural enrichment process occurring in the unsaturated zone similar to that of alluvial groundwater in arid environments in Africa and the middle east. If irrigation practices are the source of this evaporative enrichment, the sustainability of the groundwater resources could be at risk due to increasing groundwater salinity. This could have serious implications upon the economy of the region, which is production agriculture based. Whatever the source of enrichment, future land management plans in the basin will benefit from the isotopic, chemical, and on-site data found in this study.

Advisor: F. Edwin Harvey