| Description |
The Navajo Nation, located in the Four Corners region of the United States (U.S.), relies heavily upon groundwater to fulfill its water needs (over 90%). The semiarid to arid climate in the region contributes to high evaporation rates; therefore, contributing to decreased precipitation recharge to ephemeral and perennial streams, lakes, and groundwater. Prolonged drought in this region could significantly impact water resources. This dissertation research focused on quantifying precipitation amounts, characterizing precipitation, and estimating precipitation recharge, which is crucial to the vitality of the largest federally recognized land-based tribe in the U.S. In Chapter 2, we evaluated precipitation amounts at 90 precipitation sites from water year 2002 to 2015 using a vector quantization method, k-means clustering; and we quantified precipitation amounts, and described intra- and interannual precipitation. In Chapter 3, we investigated and characterized the North American monsoon (NAM) using hydrogen and oxygen stable isotopes at 39 precipitation sites from May to October from 2014 to 2017 to determine its relationship with groundwater, springs, streams, and lakes. In Chapter 4, we determined apparent ages for eight groundwater drinking wells located within the Fort Defiance, Arizona Chapter boundaries, and estimated recharge rates for the area. Based on precipitation climatology, we determined there were five distinct precipitation regions, north, east, south, west, and high mountain area, located across the Navajo Nation; we also concluded there was a bimodal precipitation regime with summer and winter iv seasonal precipitation independent of one another. An evaluation of precipitation and associated waters established the NAM stable isotopic signature was distinct compared to ground and surface waters, and we found that future changes in the NAM are less likely to impact groundwater. Investigation of groundwater in the Fort Defiance area determined apparent groundwater ages ranged from modern to Late Pleistocene ages; and concluding evidence exhibited that some wells are susceptible to modern groundwater contamination. |
