USGS

WATER-QUALITY ASSESSMENT OF THE OZARK PLATEAUS STUDY UNIT, ARKANSAS, KANSAS, MISSOURI, AND OKLAHOMA—ANALYSIS OF INFORMATION ON NUTRIENTS, SUSPENDED SEDIMENT, AND SUSPENDED SOLIDS, 1970-92

By Jerri V. Davis, James C. Petersen, James C. Adamski, and David A. Freiwald

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Abstract

Water-quality data collected during water years 1970-90 (October 1 to September 30) for 83 surface-water sites and during 1970-92 for 395 ground-water sites in the 48,000 square mile Ozark Plateaus study unit of the National Water- Quality Assessment Program were analyzed using selected descriptive and statistical methods. The water-quality data include nutrient (nitrogen and phosphorus), suspended-sediment, and suspended- solids data; and ancillary information on fertilizer use, animal waste, sewage-treatment plants, and land use.

Statistically significant differences existed in surface-water quality that can be attributed to physiography, land use, and other effects. The sites that were considered to be substantially affected by sewage-treatment plants had the largest concentrations of nutrients. Nutrient concentrations generally were larger at sites associated with agricultural basins than at sites associated with forested basins.

Statistically significant differences existed in the quality of ground water that can be attributed to hydrogeologic and land-use effects. Nutrient concentrations generally were largest where the water source is indicated to be shallow in origin and where parts of the hydrogeologic units are in agricultural land-use areas.

Water quality has changed at several surface- water sites since 1970. Nutrient concentrations appear to have increased at some sites and decreased at other sites. Causes of these apparent trends are not known, but many of the sites with apparent trends are in agricultural areas.

Surface-water loads of nutrients and suspended sediment were affected by several factors including streamflow, climate, drainage area, reservoir operation, and inputs from point and nonpoint sources. Annual loads were largest in large basins, with large inputs of nutrients or sediment during periods of high streamflows at locations where reservoir operation effects are not substantial.


TABLE OF CONTENTS

FIGURES
  1. Location of Ozark Plateaus study unit, major river basins, physiograhic areas, and hydrogeologic units
  2. Municipal sewage-treatment plant point-source discharges greater than 0.5 million gallons per day
  3. Location of selected surface-water sites with nutrient and suspended-sediment data
  4. Bar graphs showing monthly distribution of samples collected and analyzed for nitrite plus nitrate at selected surface-water sites for water years 1980-90
  5. Bar graphs showing number of samples for total phosphorus within deciles of daily mean discharge for water years 1980-90
  6. Map showing location of wells used in data analysis
  7. Map showing location of springs used in data analysis
  8. Bar graphs showing number of ground-water samples, by land use and site type, used in data analysis
  9. Bar graphs showing number of ground-water samples by confined and unconfined aquifers and temporal distribution
  10. Statistical distribution of well depth
  11. Statistical distribution of nitrite plus nitrate concentrations at surface-water sites for water years 1980-90
  12. Statistical distribution of ammonia concentrations at surface-water sites for water years 1980-90
  13. Statistical distribution of total ammonia plus organic nitrogen concentrations at surface-water sites for water years 1980-90
  14. Statistical distribution for total nitrogen concentrations at surface-water sites for water years 1980-90
  15. Statistical distribution for total phosphorus concentrations at surface-water sites for water years 1980-90
  16. Statistical distribution of orthophosphate concentrations at surface-water sites for water years 1980-90
  17. Statistical distribution of suspended-solids concentrations at surface-water sites for water years 1980-90
  18. Statistical distribution of nitrite plus nitrate concentrations at surface-water indicator and integrator sites in the Meramec, Osage, and White River Basins for water years 1980-90
  19. Statistical distribution of total phosphorus concentrations at surface-water indicator and integrator sites in the Meramec, Osage, and White River Basins for water years 1980-90
  20. Graphs showing relation of nitrite plus nitrate concentration to discharge at selected sites for water years 1980-90
  21. Graphs showing relation of total phosphorus concentration to discharge at select sites for water years 1980-90
  22. Statistical distribution of nitrite plus nitrate concentrations in ground water for water years 1970-92
  23. Statistical distribution of ammonia concentrations in ground water for water years 1970-92
  24. Statistical distribution of ammonia plus organic nitrogen concentrations in ground water for water years 1970-92
  25. Statistical distribution of total nitrogen concentrations in ground water for water years 1970-92
  26. Statistical distribution of total phosphorus concentrations in ground water for water years 1970-92
  27. Statistical distribution of orthophosphate concentrations in ground water for water years 1970-92
  28. Concentrations of nitrite plus nitrate for water years 1970-90 at selected surface-water sites
  29. Concentrations of ammonia for water years 1970-90 at selected surface-water sites
  30. Concentrations of total ammonia plus organic nitrogen for water years 1970-90 at selected surface-water sites
  31. Concentrations of total phosphorus for water years 1970-90 at selected surface-water sites
  32. Concentrations of orthophosphate for water years 1970-90 at selected surface-water sites
  33. Concentrations of suspended solids for water years 1970-90 at selected surface-water sites
TABLES
  1. Land-use percentage by physiographic area
  2. Annual nitrogen and phosphorus fertilizer use by major river basins, 1965 and 1985
  3. Animal waste nutrient contribution to the Ozark Plateaus study unit
  4. Major water-quality data sources available for the Ozark Plateaus study unit
  5. Summary by agency of the number of sites, collection methods, and frequency of water-quality samples used for analysis in this report
  6. Site and basin characteristics of surface-water sites in the Ozark Plateaus study unit
  7. Number of ground-water samples, by hydrogeologic unit, used in data analysis
  8. Statistical summary, by station, of discharge, nutrient, suspended-solids, and suspended-sediment data for surface water in the Ozark Plateaus study unit for water years 1980-90
  9. Statistical summary, by physiographic area and land use, of nutrient and suspended-solids data for surface water in the Ozark Plateaus study unit for water years 1980-90
  10. Statistical summary of nutrient data for ground water in the Ozark Plateaus study unit
  11. Ground-water samples with nitrate concentrations exceeding the maximum contaminant level
  12. Sites selected for examination of changes in water quality
  13. Ground-water sites with water-quality samples collected for more than 10 years
  14. Estimated annual inputs of nitrogen for selected basins
  15. Estimated annual inputs of phosphorus for selected basins
  16. Regression models used to estimate daily constituent loads at selected sites
  17. Estimated total nitrogen, total phosphorus, and suspended-sediment loads and yields at selected sites
  18. Annual mean streamflow for sites used for load estimation

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