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Nutrients National Synthesis Project

Transport and Fate of Nitrate and Pesticides: Hydrogeology and Riparian Zone Processes

By Larry J. Puckett and W. Brian Hughes

Abstract
There is continuing concern over potential impacts of widespread application of nutrients and pesticides on ground- and surface-water quality. Transport and fate of nitrate and pesticides were investigated in a shallow aquifer and adjacent stream, Cow Castle Creek, in Orangeburg County, South Carolina. Pesticide and pesticide degradate concentrations were detected in ground water with greatest frequency and largest concentrations directly beneath and downgradient from the corn (Zea mays L.) field where they were applied. In almost all samples in which they were detected, concentrations of pesticide degradates greatly exceeded those of parent compounds, and were still present in ground waters that were recharged during the previous 18 yr. The absence of both parent and degradate compounds in samples collected from deeper in the aquifer suggests that this persistence is limited or that the ground water had recharged before use of the pesticide. Concentrations of NO₃^- in ground water decreased with increasing depth and age, but denitrification was not a dominant controlling factor. Hydrologic and chemical data indicated that ground water discharges to the creek and chemical exchange takes place within the upper 0.7 m of the streambed. Ground water had its greatest influence on surface-water chemistry during low-flow periods, causing a decrease in concentrations of Cl^-, NO₃^-, pesticides, and pesticide degradates. Conversely, shallow subsurface drainage dominates stream chemistry during high-flow periods, increasing stream concentrations of Cl^-, NO₃^-, pesticides, and pesticide degradates. These results point out the importance of understanding the hydrogeologic setting when investigating transport and fate of contaminants in ground water and surface water.

Table of Contents

Study area

Methods
  Water Sample Collection
  Sediment Analysis
  Water Sample Analysis
  Dissolved Gases
  Chlorofluorocarbon Age Dating

Results
  Surface Water Hydrology
  Surface Water Chemistry
  Ground Water Hydrology
  Sediment Chemistry
  Dissolved Gases
  Chlorofluorocarbon Age Dates
  Ground Water Chemistry

Discussion
  Nitrate Transport and Fate
  Pesticides and Pesticide Degradates
  Hydrogeologic Controls

Conclusions

Acknowledgments

References

• Report (0.9 mb PDF)