The overarching objective of this dissertation was to study groundwater resources on global, local, and regional scales. The first objective of this dissertation was to analyze the groundwater nitrate contamination in the Edwards-Trinity and the Southern High-Plains aquifers of Texas. The second was to study groundwater quality in terms of seawater intrusion in the California Coastal Basin, Upper Floridian, and North Atlantic Coastal Plain aquifers. This dissertation also provided a comprehensive overview of the groundwater level in basins at the global scale and further analyzed agricultural activities on groundwater storage in small and large basins. To achieve first objective, Ordinary Least Square (OLS) and Geographically Weighted Regression (GWR) models were used to study the relationship between groundwater nitrate contamination and land use. This dissertation further identified dominant groundwater types using USGS well data and to estimate the extent of seawater intrusion in terms of dominant ions and ocean salinity in the United States coastal aquifers. Finally, groundwater storage anomaly was quantified using Gravity Recovery and Climate Experiment (GRACE) derived variations in total Terrestrial Water Storage (TWS) and the Global Land Data Assimilation System (GLDAS). Land cover data representing a percentage of irrigated lands using groundwater resources was used to study agricultural activities on groundwater storage. Groundwater nitrate contamination was positively associated with cotton production in Southern High-Plains and Edwards-Trinity aquifers. The nitrate concentrations tended to increase as the well-depth decreased in both aquifers. Results showed that the dominant ions in the study area were Na+ and Cl- . The study concluded that Na-Cl and mixed Ca-Mg-Cl were dominant water types in the United States' coastal aquifers. Results also indicated that seawater intrusion is occurring in the US coastal aquifers. Groundwater depletion has increased in southern Asia, western North America, and southwestern Europe due to groundwater withdrawal for agricultural use. However, farming practice is not the main reason for groundwater scarcity in South America, Africa, and Australia.
| Identifer | oai:union.ndltd.org:MSSTATE/oai:scholarsjunction.msstate.edu:td-3417 |
| Date | 09 August 2019 |
| Creators | Lotfata, Aynaz |
| Publisher | Scholars Junction |
| Source Sets | Mississippi State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
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