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| Kentucky Water Science Center |
U.S. Geological Survey, Scientific Investigations Report 2006-5204
By Angela S. Crain
In cooperation with the Kentucky Department of Agriculture
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Nutrients, primarily nitrogen and phosphorus compounds, naturally occur but also are applied to land in the form of commercial fertilizers and livestock waste to enhance plant growth. Concentrations, estimated loads and yields, and sources of nitrite plus nitrate, total phosphorus, and orthophosphate were evaluated in streams of the Little River Basin to assist the Commonwealth of Kentucky in developing “total maximum daily loads” (TMDLs) for streams in the basin. The Little River Basin encompasses about 600 square miles in Christian and Trigg Counties, and a portion of Caldwell County in western Kentucky. Water samples were collected in streams in the Little River Basin during 2003-04 as part of a study conducted in cooperation with the Kentucky Department of Agriculture. A total of 92 water samples were collected at four fixed-network sites from March through November 2003 and from February through November 2004. An additional 20 samples were collected at five synoptic-network sites during the same period.
Median concentrations of nitrogen, phosphorus, and suspended sediment varied spatially and seasonally. Concentrations of nitrogen were higher in the spring (March-May) after fertilizer application and runoff. The highest concentration of nitrite plus nitrate—5.7 milligrams per liter (mg/L)—was detected at the South Fork Little River site. The Sinking Fork near Cadiz site had the highest median concentration of nitrite plus nitrate (4.6 mg/L).
The North Fork Little River site and the Little River near Cadiz site had higher concentrations of orthophosphate in the fall and lower concentrations in the spring. Concentrations of orthophosphate remained high during the summer (June-August) at the North Fork Little River site possibly because of the contribution of wastewater effluent to streamflow. Fifty-eight percent of the concentrations of total phosphorus at the nine sites exceeded the U.S. Environmental Protection Agency recommended maximum concentration limit of 0.1 mg/L.
Concentrations of suspended sediment were highest in the spring during runoff and lowest in the fall. The highest concentration of suspended sediment (1,020 mg/L) was observed at the Sinking Fork near Cadiz site. The median concentration of suspended sediment for all sites sampled was 12 mg/L. A nonparameteric statistical test (Wilcoxson rank-sum) showed that the median concentrations of suspended sediment were not different among any of the fixed-network sites.
The Little River near Cadiz site contributed larger estimated mean annual loads of nitrite plus nitrate (2,500,000 pounds per year (lb/yr)) and total phosphorus (160,000 lb/yr) than the other three fixed-network sites. Of the two main upstream tributaries from the Little River near Cadiz site, the North Fork Little River was the greatest contributor of total phosphorus to the study area with an estimated mean annual load of 107,000 lb/yr or about 64 percent of the total estimated mean annual load at the Little River near Cadiz site. The other main upstream tributary, South Fork Little River, had an estimated mean annual load of total phosphorus that was about 20 percent of the mean annual load at the Little River near Cadiz site. Estimated loads of suspended sediment were largest at the Little River near Cadiz site, where the estimated mean annual load for 2003-04 was about 84,000,000 lb/yr. The North Fork Little River contributed an estimated 36 percent of the mean annual load of suspended sediment at the Little River near Cadiz site, while the South Fork Little River contributed an estimated 18 percent of the mean annual load at the Little River near Cadiz site.
The North Fork Little River site had the largest estimated mean annual yield of total phosphorus (1,600 pounds per year per square mile (lb/yr/mi2)) and orthophosphate (1,100 lb/yr/mi2). A principal source of phosphorus for the North Fork Little River is discharge from wastewater-treatment facilities. The largest estimated mean annual yield of nitrite plus nitrate was observed at the South Fork Little River site. The North Fork Little River site had the largest estimated mean annual yield of suspended sediment (450,000 lb/yr/mi2).
Inputs of nitrogen and phosphorus to streams from point and nonpoint sources were estimated for the Little River Basin. Commercial fertilizer and livestock-waste applications on row crops are a principal source of nutrients for most of the Little River Basin. Sources of nutrients in the urban areas of the basin mainly are from effluent discharge from wastewater-treatment facilities and fertilizer applications to lawns and golf courses.
Abstract
Introduction
Purpose and Scope
Description of the Little River Basin
Geology
Streamflow
Land Use
Study Design and Methods
Sample-Site Selection and Sampling Frequency
Sampling Methods
Analytical Methods
Quality Control
Statistical Analysis of Nutrients and Suspended Sediment
Load-Estimation Methods
Sources of Nitrogen and Phosphorus
Nonpoint-Source Contributions
Atmospheric Deposition
Commercial Fertilizer and Livestock Waste
Nitrogen Fixation by Soybeans
Point-Source Contributions
Concentrations, and Estimated Loads and Yields of Nutrients
Concentrations
Spatial Variability
Seasonal Variability
Estimated Loads and Yields
Concentrations, and Estimated Loads and Yields of Suspended Sediment
Concentrations
Spatial Variability
Seasonal Variability
Estimated Loads and Yields
Conclusions
Acknowledgments
References Cited
Appendix 1: Statistical summary of concentrations of ammonia nitrogen, nitrite plus nitrate, total phosphorus, orthophosphate, and suspended sediment in the Little River Basin, Kentucky, 2003-04
1-5. Maps showing:
1. Location of the surface-water-sampling sites in the Little River Basin, Kentucky, 2003-04.
2. Surficial geology in the Little River Basin, Kentucky, 2003-04.
3. Location of sinkholes in the Little River Basin, Kentucky, 2003-04.
4. Location of surface-water samplings sites and graphs showing precipitation and daily mean streamflow at selected sites in the Little River Basin, Kentucky, 2003-04.
5. Land cover in the Little River Basin, Kentucky, 2001.
6-10. Boxplots showing:
6. Concentrations of nitrite plus nitrate, total phosphorus, and orthophosphate at all sampling sites in the Little River Basin, Kentucky, 2003-04.
7. Seasonal distribution of concentrations of nitrite plus nitrate for four fixed-network sites in the Little River Basin, Kentucky, 2003-04.
8. Seasonal distribution of concentrations of total phosphorus and orthophosphate for four fixed-network sites in the Little River Basin, Kentucky, 2003-04.
9. Concentrations of suspended sediment at all sampling sites in the Little River Basin, Kentucky, 2003-04.
10. Seasonal distribution of concentrations of suspended sediment for four fixed-network sites in the Little River Basin, Kentucky, 2003-04.
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Suggested Citation:
Crain, Angela S., 2006, Concentrations, and Estimated Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Kentucky, 2003-04: U.S. Geological Survey Scientific Investigations Report 2006-5204, 31 p.
For more information about USGS activities in Kentucky, visit the USGS Kentucky Water Science Center home page.
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