Evaluation of Nitrate Contamination in Major Porous Media Aquifers in Texas

This study aimed to evaluate the factors influencing nitrate contamination in major porous media aquifers across Texas by analyzing groundwater nitrate concentration data alongside nitrogen loading and aquifer susceptibility parameters. Attributes related to nitrogen loading included atmospheric deposition, fertilizers, land use, sewage and septic input proxies, population density, precipitation, and irrigation. Aquifer susceptibility attributes included land surface slope, soil drainage, clay content, and organic matter content. Multivariate logistic regression was employed to assess the probability of nitrate concentrations exceeding 4 mg/L nitrate-N in shallow wells (≤ 30 m) based on these variables.

The final regression model incorporated precipitation, percentage of agricultural land, low-density residential land, and soil organic matter. Observed and predicted probabilities of elevated nitrate concentrations showed strong correlation in both calibration and validation datasets. The inverse relationship between precipitation and nitrate concentration may indicate dilution in high precipitation areas and possible evapoconcentration in low precipitation areas. While nitrate loading was not explicitly included in the model, agricultural land percentage served as a proxy for nitrogen loading from agricultural sources, and low-density residential land use served as a proxy for septic tank effluent. The percentage of organic matter may reflect denitrification in certain regions.

This GIS and logistic regression analysis offers valuable insights into the factors influencing nitrate concentrations in groundwater. Future studies should complement this analysis with field sampling to validate the GIS and logistic regression findings and assess the impact of processes like dilution and denitrification on nitrate concentrations.