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NUTRIENTS AND PESTICIDES IN GROUND WATER OF THE OZARK PLATEAUS IN ARKANSAS, KANSAS, MISSOURI, AND OKLAHOMA

by James C. Adamski

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Abstract

A total of 229 ground-water samples were collected from 215 sites as part of the Ozark Plateaus study unit of the National Water-Quality Assessment Program. These samples were collected from 1993 through 1995 using a network of springs and wells with three scale-dependent components. The first component, the study-unit survey, consisted of 99 randomly selected springs and domestic wells in the Springfield Plateau and Ozark aquifers. The second component, two land-use studies, consisted of 42 springs and domestic wells in a poultry-dominated agricultural area and 40 springs and domestic wells in a cattle-dominated agricultural area overlying the Springfield Plateau aquifer. The third component, the small-watershed study, consisted of 4 springs, 18 domestic wells, and 11 monitoring wells in a small basin within the poultry land-use study area. Samples were analyzed for major ions, nutrients, dissolved organic carbon, methylene blue active substances, tritium, and 88 pesticides and metabolites.The water-quality data from these samples were analyzed with descriptive and statistical methods.

Nitrite plus nitrate, which was detected more often and in greater concentrations than any of the other nutrients, ranged from less than 0.05 to 25 milligrams per liter as nitrogen. Nitrite plus nitrate concentrations positively correlated to percent agricultural land use around each site. Median nitrite plus nitrate concentrations generally were greater in samples from springs than in samples from wells. Concentrations of nitrite, ammonia, and ammonia plus organic nitrogen were also affected by land use and also by concentrations of dissolved oxygen in the ground water. Concentrations of phosphorus and orthophosphate probably were affected by land use and also by phosphorus solubility.

Pesticides were detected in 80 of 229 samples from 73 of 215 sites. A total of 20 pesticides were detected with a maximum of 5 pesticides detected in any 1 sample. The most commonly detected pesticides were tebuthiuron, atrazine, prometon, desethylatrazine, and simazine. Maximum concentrations ranged from 0.003 to 1.0 microgram per liter. The occurrence and distribution of pesticides were related to land use. Percent agricultural land use was greater for samples with pesticides detected than for samples with no pesticides detected. Pesticides were detected more often in samples from springs than in samples from wells. The occurrence of pesticides also was related to seasonality and chemical characteristics, such as solubility and persistence, of the compounds.


TABLE OF CONTENTS

ILLUSTRATIONS
  1. Location of Ozark Plateaus study unit, physiographic areas, and surficial extent of hydrogeologic units
  2. Generalized land use in the Ozark Plateaus study unit
  3. Location of springs and wells in the Ozark Plateaus study unit sampled for the study-unit survey, the poultry and cattle land-use studies, and the small-watershed study
  4. Boxplots showing distribution of spring discharge and well depth of sites sampled for the study-unit survey, and the poultry and cattle land-use studies
  5. Boxplots showing distribution of agricultural land use and forested land cover within probable recharge basins of springs and within 1-mile radius of wells sampled for the study-unit survey, and the poultry and cattle land-use studies
  6. Map showing concentrations of nitrite plus nitrate in ground-water samples collected from springs, domestic wells, and monitoring wells
  7. Boxplot showing distribution of nitrite plus nitrate concentrations in ground-water samples collected for the study-unit survey, and the poultry and cattle land-use studies
  8. Graph showing relation of nitrite plus nitrate concentrations to agricultural land use and forested land cover for ground-water samples from (a) springs and domestic wells, (b) springs and domestic wells, (c) springs, and (d) domestic wells
  9. Graph showing relation of nitrite plus nitrate concentrations and dissolved oxygen in ground-water samples from domestic wells
  10. Boxplot showing distribution of ammonia concentrations in ground-water samples collected from springs, domestic wells, and monitoring wells
  11. Boxplot showing distribution of orthophosphate concentrations in ground-water samples collected for the study-unit survey, and the poultry and cattle land-use studies
  12. Map showing locations of sampled springs, domestic wells, and monitoring wells with detectable concentrations of pesticides
  13. Boxplot showing relation of agricultural land use and forested land cover to pesticide detections in ground-water samples
  14. Boxplot showing relation of spring discharge to pesticide detections in ground-water samples from agricultural areas overlying the Springfield Plateau aquifer
TABLES
  1. Summary of number and type of ground-water sampling sites for each network component in the Ozark Plateaus study unit
  2. Statistical summary of nutrient data for filtered ground-water samples in the Ozark Plateaus study unit collected during 1993-95
  3. Concentrations of nitrite, nitrite plus nitrate, ammonia, and ammonia plus organic nitrogen in filtered samples collected from monitoring wells in April and July 1995 during the small watershed study
  4. Number of pesticide detections and range of concentrations

U.S. Department of the Interior, U.S. Geological Survey
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Last modified: Thursday, September 01 2005, 05:14:33 PM
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