“OCCURRENCE OF NITRATE IN THE NEBRASKA’S GROUNDWATER SYSTEM: IDENTIFYING FACTORS, EXAMINING THE BEST MANAGEMENT PRACTICES, AND ANALYZING COSTS”

Advisor: Dr. Chittaranjan Ray

Understanding the occurrence of nitrate in the Nebraska’s groundwater system and the protection of groundwater from contamination is one of the challenges in the conservation of Nebraska’s drinking water resources. The main objectives of this research were to identify the influential factors associated with groundwater nitrate concentrations in Nebraska using the Classification and Regression Tree (CART) model, examine the Best Management Practices (BMPs) and future climatic scenarios affecting soil water and nitrate-N transport in the deep vadose zone using the Root Zone Water Quality Model (RZWQM2), and assess costs of nitrate contamination of groundwater in Nebraska’s domestic wells resulting from intensive agriculture using the Multiple Logistic Regression Model (MLRM) and Life Cycle Costing (LCC).

The influence of physical factors on groundwater nitrate concentrations correspond with vadose zone thickness, effective hydraulic conductivity, and saturated thickness in the west, while in eastern Nebraska, concentrations are correlated with average percent sand in the topsoil (0-150 cm), well depth, and effective hydraulic conductivity.

The conversion of gravity to sprinkler irrigation can reduce nitrate-N losses to groundwater. Rotating corn and soybean is an efficient management practice to lower nitrate-N concentrations in the deep vadose zone, compared with continuous corn. Transitioning from dryland production to irrigation can lead to increased nitrate-N concentrations. Splitting nitrogen fertilizer application can reduce nitrate-N losses to groundwater. Nitrate-N transport in the deep vadose zone is higher at the irrigated site than non-irrigated site under the future climatic scenarios.
A reverse osmosis Point-of-Use (POU) treatment is the option with the lowest costs for a household, but the biological denitrification Point-of-Entry (POE) treatment system is most likely to be suitable with lower treatment costs for a community.