USGS Home
Contact USGS
Search USGS

 Go to:      NAWQA Home     National-Synthesis Assessments

Nutrients National Synthesis Project

Nitrate Behavior in Ground Waters of the Southeastern United States

By Bernard T. Nolan

Abstract
Principal components analysis (PCA) was performed with water-quality data from studies conducted during 1993-1995 to explore potential nitrate-attenuation processes in ground waters of the southeastern United States. Nitrate reduction is an important attenuation process in selected areas of the Southeast. A "nitrate-reduction" component explains 23% of the total variance in the data and indicates that nitrate and dissolved oxygen are inversely related to ammonium, iron, manganese, and dissolved organic carbon. Additional components extracted by PCA include "calcite dissolution" (18% of variance explained) and "phosphate dissolution" (9% of variance explained). Reducing conditions in ground waters of the region influence nitrate behavior through bacterially mediated reduction in the presence of organic matter, and by inhibition of nitrate formation in anoxic ground water beneath forested areas. Component scores are consistent with observed water-quality conditions in the region. For example, median nitrate concentration in ground-water samples from the ALBE Coastal Plain is <0.05 mg/L, median dissolved organic carbon concentration is 4.2 mg/L, and median dissolved oxygen (DO) concentration is 2.1 mg/L, consistent with denitrification. Nitrate reduction does not occur uniformly throughout the Southeast. Median DO concentrations in ground-water samples from the Apalachicola-Chattahoochee-Flint River Basin are 6.2-7.1 mg/L, and median nitrate concentrations are 0.61-2.2 mg/L, inconsistent with denitrification. Similarly, median DO concentration in samples from the Georgia-Florida Coastal Plain is 6.0 mg/L and median nitrate concentration is 5.8 mg/L.

Table of Contents
Background
Methods
Results and discussion
  Component loadings
      Biologically mediated transformation of nitrate, iron, and manganese
      Calcite dissolution
      Phosphate dissolution
  Component scores
Conclusions
Acknowledgments
References

• Report (0.1 mb PDF)