Water-Quality Assessment of the Ozark Plateaus Study Unit, Arkansas, Kansas, Missouri, and Oklahoma-Nutrients, Bacteria, Organic Carbon, and Suspended Sediment in Surface Water, 1993-95
By JERRI V. DAVIS and RICHARD W. BELL
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Abstract
Nutrient, bacteria, organic carbon, and suspended-
sediment samples were collected from
1993-95 at 43 surface-water-quality sampling
sites within the Ozark Plateaus National Water-
Quality Assessment Program study unit. Most
surface-water-quality sites have small or medium
drainage basins, near-homogenous land uses (primarily
agricultural or forest), and are located predominantly
in the Springfield and Salem Plateaus.
The water-quality data were analyzed using
selected descriptive and statistical methods to
determine factors affecting occurrence in streams
in the study unit.
Nitrogen and phosphorus fertilizer use
increased in the Ozark Plateaus study unit for the
period 1965-85, but the application rates are well
below the national median. Fertilizer use differed
substantially among the major river basins and
physiographic areas in the study unit. Livestock
and poultry waste is a major source of nutrient
loading in parts of the study unit. The quantity of
nitrogen and phosphorus from livestock and poultry
wastes differed substantially among the river
basins of the study unit's sampling network.
Eighty six municipal sewage-treatment plants in
the study unit have effluents of 0.5 million gallons
per day or more (for the years 1985-91).
Statistically significant differences existed
in surface-water quality that can be attributed to
land use, physiography, and drainage basin size.
Dissolved nitrite plus nitrate, total phosphorus,
fecal coliform bacteria, and dissolved organic carbon
concentrations generally were larger at sites
associated with agricultural basins than at sites
associated with forested basins. A large difference
in dissolved nitrite plus nitrate concentrations
occurred between streams draining basins with
agricultural land use in the Springfield and Salem
Plateaus. Streams draining both small and
medium agricultural basins in the Springfield Plateau
had much larger concentrations than their
counterparts in the Salem Plateau. Drainage basin
size was not a significant factor in affecting total
phosphorus, fecal coliform bacteria, or dissolved
organic carbon concentrations. Suspended-sediment
concentrations generally were small and
indicative of the clear water in streams in the
Ozark Plateaus.
A comparison of the dissolved nitrite plus
nitrate, total phosphorus, and fecal coliform data
collected at the fixed and synoptic sites indicates
that generally the data for streams draining basins
of similar physiography, land-use setting, and
drainage basin size group together. Many of the
variations are most likely the result of differences
in percent agricultural land use between the sites
being compared or are discharge related. The relation
of dissolved nitrite plus nitrate, total phosphorus,
and fecal coliform concentration to
percent agricultural land use has a strong positive
2 Water-Quality Assessment-Nutrients, Bacteria, Organic Carbon, and Suspended Sediment in Surface Water, 1993-95
correlation, with percent agricultural land use
accounting for between 42 and 60 percent of the
variation in the observed concentrations.
TABLE OF CONTENTS
- Abstract
- Introduction
- Description of the Ozark Plateaus Study Unit
- Hydrology
- Climate, Population, Land Use, and Water Use
- Nitrogen and Phosphorus Fertilizer Use
- Animal and Municipal Sources of Nutrients
- Description of Surface-Water-Quality Sampling Network
- Basic-Fixed and Intensive-Fixed Sites
- Synoptic Sites
- Assessment of Conditions
- Study Approach
- Nutrients
- Dissolved Nitrite Plus Nitrate
- Total Phosphorus
- Fecal Indicator Bacteria
- Organic Carbon
- Suspended Sediment
- Summary
- Selected References
FIGURES
- Location of Ozark Plateaus study unit, major river basins, and physiographic areas
- Land use in the Ozark Plateaus study unit
- Municipal sewage-treatment plant point-source discharges greater than 0.5 million gallons per day
- Location of sampling sites comprising the surface-water sampling network
- Graphs showing number of samples for total phosphorus within deciles of daily mean discharge for water years 1993-95
- Boxplots showing statistical distribution of dissolved nitrite plus nitrate concentrations at selected surface-water fixed sites for water years 1993-95
- Graphs showing comparison of dissolved nitrite plus nitrate data collected at fixed and synoptic sites May 1994 and 1995 and August or September 1994
- Graph showing relation of dissolved nitrite plus nitrate concentrations to the percentage of agricultural
land use
- Map showing areal distribution of median dissolved nitrite plus nitrate concentrations at fixed and
synoptic sites for water years 1993-95
- Graphs showing relation of dissolved nitrite plus nitrate concentrations to discharge at fixed sites for water years 1993-95
- Boxplots showing statistical distribution of total phosphorus concentrations at selected surface-water fixed sites for water years 1993-95
- Comparison of total phosphorus data collected at fixed and synoptic sites May 1994 and 1995 and August or September 1994
- Comparison of instantaneous discharge at fixed and synoptic sites May 1994 and 1995 and August or September 1994
- Relation of total phosphorus concentrations to discharge at fixed sites for water years 1993-95
- Relation of total phosphorus concentrations to the percentage of agricultural land use
- Boxplots showing statistical distribution of fecal coliform counts at selected surface-water fixed sites for water years 1993-95
- Comparison of fecal coliform data collected at fixed and synoptic sites May 1994 and 1995 and August or September 1994
- Relation of fecal coliform counts to discharge at fixed sites for water years 1993-95
- Relation of fecal coliform counts to the percentage of agricultural land use
- Boxplots showing statistical distribution of dissolved organic carbon concentrations at selected surfacewater fixed sites for water years 1993-95
- Boxplots showing statistical distribution of suspended-sediment concentrations at selected surfacewater
fixed sites for water years 1993-95
TABLES
- Land-use percentage by physiographic area
- Annual nitrogen and phosphorus fertilizer use by major river basins, 1965 and 1985
- Animal waste nutrient contribution to the study unit
- Estimated contributions of nitrogen and phosphorus in animal waste to selected sampling sites within the study unit surface-water sampling network
- Site and basin characteristics of sampling sites within the sampling network
- Statistical summary of discharge, nutrient, indicator bacteria, dissolved and suspended organic carbon, and suspended-sediment data for surface-water fixed sites in the Ozark Plateaus study unit for water years 1993-95
- Median fecal coliform to Escherichia coli ratios at fixed sites for water years 1993-95
- Median dissolved organic carbon to suspended organic carbon ratios at fixed sites for water years 1993-95