Date of Award
8-2025
Degree Type
Creative Project
Degree Name
Master of Natural Resources (MNR)
Department
Natural Resources
Committee Chair(s)
Sunshine Brosi (Committee Chair)
Committee
Sunshine Brosi
Abstract
In Southeastern Utah, springs play a critical role in sustaining groundwater-dependent ecosystems (GDEs) in a semi-arid environment. However, they remain understudied and face growing threats from climate change, land use modifications, and hydrologic alterations. This study addresses knowledge gaps in spring occurrence, hydrologic function, and ecological condition by integrating field surveys, remote sensing, and geospatial analysis across multiple spatial scales. It provides a comprehensive assessment of spring hydrology, water quality, and ecological conditions using field surveys, remote sensing, and GIS analysis to establish a foundational baseline of GDE resources in the region. I applied a multi-scale monitoring approach across the La Sal and Abajo Mountains, covering 59 HUC-12 subwatersheds from 2020 to 2024. During this period, inventory and measurements were taken for water quality, discharge, vegetation composition, disturbances, and developments. A total of 382 previously undocumented springs were discovered across the La Sal and Abajo Mountain ranges, which brought the total number of known springs to 597.
For discharge measurements, the results show that higher-elevation springs that emerge from unconsolidated sediments where snowpack is greatest, exhibit the highest flow rates. These springs typically emerge at the base of steep slopes where unconsolidated materials meet finer sediments with silts and clay particles. By contrast, most springs have significantly lower discharge rates and originate from precipitation that infiltrates coarse or fractured sedimentary aquifers. As the water percolates downward through these coarse sedimentary formations, it encounters lower permeable geologic formations or aquitards, which causes water to move laterally until it emerges at the surface as a spring. Using a combination of field-verified spring locations, geologic mapping, and topographic analysis, this study delineated the recharge areas and discharge zones, which helped identify the boundaries of the major aquifer systems within the La Sal and Abajo Mountains. The resulting aquifer maps will provide spatially explicit guidance for future surface management actions aimed at protecting groundwater.
Vegetation composition was surveyed across spring sites to evaluate ecological integrity and wetland condition, with particular focus on wetland indicator species as a proxy for hydrologic permanence and ecological resilience. GDEs with a greater proportion of wetland indicator species were interpreted as having a more robust wetland function and greater resistance to disturbances. In addition to dominant GDE vegetation, broader landscape-scale vegetation types surrounding each GDE were also assessed to contextualize site condition within the larger ecological setting.
As part of this study, a Water Quality Index (WQI) was developed to quantify and compare spring water quality across varying geologic and ecological settings. The WQI showed that lithology and elevation are interconnected within this region and have the largest influence on water quality. Springs at lower elevations tend to have higher salinity, conductivity, and TDS, which is attributed to longer water residence time within more soluble sediments. In contrast, there appears to be much higher quality of water within formations consistent of intrusive igneous, crystalline rocks. Other factors that play a role in water quality were shown to be livestock and ungulate use within spring sites. Sites highly affected by ungulate and livestock use had higher TDS, specific conductivity and lower dissolved oxygen (DO), but showed to be only statistically significant within the La Sal Mountains.
To complement field-based measurements and extend the spatial scope of this study, remote sensing and geospatial analysis were used to investigate broader landscape patterns. Normalized Differential Vegetation Index (NDVI) and Normalized Differential Moisture Index (NDMI) served three main purposes in this study. 1) A tool for identifying undocumented GDE’s: While the remote sensing test did identify very large GDE’s, the 30m resolution of Landsat imagery was far too coarse for accurately detecting the majority of springs. 2) To determine the landscape-scale vegetation response to precipitation variability and determine correlations: The analysis showed a very weak and insignificant correlation between same-year precipitation and vegetation production or greenness. A one-year delayed correlation slightly improved the correlation between precipitation and greenness in the Abajo Mountains. This increased delayed correlation could suggest that groundwater storage and soil moisture retention play a larger role in vegetation trends than annual precipitation alone. 3) To test and determine if grazing has a significant effect on landscape-scale NDVI values between grazed allotments and ungrazed control allotments: A statistical comparison of NDVI between the grazed and ungrazed allotment from 1999 to 2024 showed no statistically significant difference in mean NDVI values. Beyond individual spring sites, a broad livestock pressure analysis was conducted using a Livestock Impact Index (LLI), which used a combination of factors such as stocking density, days of use, precipitation-weighted average, and availability of water sources. The index incorporated data from 1999 to 2024, and the primary purpose for it was to assist land managers and range conservationists on which allotments may have the potential for most livestock impacts within GDE’s.
Lastly, this study used spatial interpolation to show long-term precipitation and temperature trends from 1999 to 2024. Data show that the La Sal Mountains receive an average of 21.4 inches of precipitation annually, while the Abajo Mountains receive 18.4 inches. The highest recorded precipitation occurred in 2015, and the lowest in 2020. A slight decrease in precipitation was observed, with reductions of 19 millimeters per decade in the La Sals and 9 millimeters per decade in the Abajos, though interannual variability remains the dominant factor. Temperature trends show a slight warming, with mean annual temperatures of 7.6°C in the La Sals and 8.3°C in the Abajos. The warmest year was 2017, while the coldest were 2011 (La Sals) and 2008 (Abajos). Temperature increases of 0.017°C per decade in the La Sals and 0.161°C per decade in the Abajos were observed.
Recommended Citation
Lay, Colten, "Groundwater-Dependent Ecosystems in Southeastern Utah: An Integrated Analysis of Hydrology, Ecology, and Landscape Change" (2025). All Graduate Reports and Creative Projects, Fall 2023 to Present. 103.
https://digitalcommons.usu.edu/gradreports2023/103
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