Load calculations based on National 

Stream Quality Accounting Network 

(NASQAN) data appear to indicate that the 

Cumberland and Green River Basins in 

Kentucky have the highest annual yields of 

atrazine, simazine, and metolachlor runoff in 

the country. These yields represent from 9 to 

28 percent of the amount of these herbicides 

used in the Cumberland and Green River 

Basins on agricultural fields in 1997.

NATIONAL STREAM QUALITY 

ACCOUNTING NETWORK 

PROGRAM

The U.S. Geological Survey (USGS) 

operates streamflow and water-quality 

sampling sites in the Ohio River Basin as 

part of the NASQAN program. The load 

(the mass of material passing a fixed point 

per unit of time) of selected herbicides in the 

Ohio River Basin was calculated using 

NASQAN data for 1997–2000. The 

streamflow and sampling stations are located 

on the main stem of the Ohio River and some 

of its major tributaries (the Wabash and the 

Tennessee). The stations are located above 

the confluences of major tributaries with the 

Ohio River or where the water quality in the 

Ohio River is expected to change. 

DESCRIPTION OF THE 

STREAMFLOW AND 

WATER-QUALITY 

SAMPLING NETWORK

Five NASQAN sampling sites were 

selected in the Ohio River Basin to monitor 

the loads of materials within the basin (fig.1 

and table 1). Three sampling sites are located 

on the main stem of the Ohio River, and two 

sampling sites are on major tributaries to the 

Ohio River (the Wabash and the Tennessee). 

The Upper-Ohio River Basin is monitored at 

Greenup Dam, Kentucky (fig. 1, map 

number 1). Extensive coal mining is a major 

land-use activity in this part of the Ohio 

River Basin but the water quality in the Ohio 

River also is affected by agriculture, forest, 

and large urban areas such as Pittsburgh, 

Pennsylvania. The Middle-Ohio River Basin 

is monitored at Cannelton Dam, Kentucky 

(fig. 1, map number 2), and represents 

predominantly forest and agricultural land 

uses, although the large urban areas of 

Louisville, Ky. and Cincinnati, Ohio also 

affect water quality. The Wabash River Basin 

is monitored at New Harmony, Indiana 

(fig. 1, map number 3), and the land use is 

largely agriculture with about two-thirds of 

the basin being devoted to row crops. 

THE LOADS OF SELECTED HERBICIDES IN THE 

OHIO RIVER BASIN, 1997–2000

U.S. Department of the Interior USGS Fact Sheet 089-02

U.S. Geological Survey November 2002

Figure 1. Location of data-collection sites in the Ohio River 

Basin, 1997–2000.

Table 1. Data-collection sites in the Ohio River Basin, 1997–2000

[km2, square kilometers]

Map

number

(fig. 1)

Site 

number Site name Basin

Drainage 

area

(km2)

1 03216600 Ohio River at Greenup Dam, Kentucky Upper-Ohio 160,000

2 03303280 Ohio River at Cannelton Dam, Kentucky MiddleOhio250,000

3 03378500 Wabash River at New Harmony, Indiana Wabash 76,000

4 03609750 Tennessee River at Highway 60 near Paducah, 

Kentucky

Tennessee 106,000

5 03612500 Ohio River near Grand Chain, Illinois Lower-Ohio 527,000
The Tennessee River Basin—the largest Ohio 

River tributary basin—is monitored near 

Paducah, Ky. (fig. 1, map number 4). This 

site is located downstream of Kentucky Dam, 

and the flow is regulated. This site represents 

a large drainage area that reflects the effects 

of forest, agriculture, and highly urbanized 

land uses. The Ohio River near Grand Chain, 

Illinois (fig. 1, map number 5), integrates the 

effects of the many different types of land 

uses throughout the Ohio River Basin. 

All sites were sampled 12 to 15 times 

per year with an emphasis on spring highflow conditions. Samples were collected 

every 2 weeks during peak pesticide-runoff 

periods (April–June), but only once every 4 

to 6 weeks for all other months. Water 

samples were depth and width integrated and 

flow weighted as described in Edwards and 

Glysson (1988) and Shelton (1994). 

Pesticide samples were composited in a glass 

carboy, filtered immediately using a 

0.7-micrometer pore-diameter glass fiber 

filter, and shipped on ice to the USGS 

National Water-Quality Laboratory (NWQL) 

in Denver, Colorado.

LOAD OF ATRAZINE, 

SIMAZINE, AND 

METOLACHLOR 

The Ohio River Basin encompasses 

portions of 14 States (fig. 1) with an area of 

526,000 square kilometers. Every year 

millions of pounds of herbicides are applied 

to crops throughout the Ohio River Basin to 

increase crop production (Ohio River Valley 

Water Sanitation Commission, 1997) and for 

safety and aesthetic purposes in urban areas. 

Storm-water runoff transports some of these 

herbicides to streams, sometimes causing 

their concentrations to reach levels that may 

have adverse ecological effects. Some of the 

most commonly applied herbicides in the 

Ohio River Basin are atrazine, simazine, and 

metolachlor (Kentucky Natural Resources 

and Environmental Protection Cabinet, 

2000). All three herbicides are classified 

Federally as "restricted-use" herbicides. 

The mean annual load (1997–2000) for 

atrazine, simazine, and metolachlor was 

estimated by interpolating between 

measurements and determining a mean daily 

concentration. To calculate the mean daily 

load, the mean daily herbicide concentration 

was multiplied by the mean daily flow 

table 2. Herbicide concentrations reported as 

being below the laboratory-reporting limit 

were set to zero for the calculation of the 

mean daily load.

Yields are defined as the amount of load 

per unit area and are useful for comparing 

basins with varying land use and agricultural 

practices. Incremental yields of a specific 

subbasin were determined by subtracting 

upstream loads from the subbasin outlet load 

and dividing by the basin area (Hooper and 

others, 2001; Kelly and others, 2001). 

Incremental yields for atrazine are presented 

in figure 2. Estimated yields of atrazine, 

simazine, and metolachlor for the Ohio River 

Basin are presented in table 2. The estimated 

yields of these herbicides in the Lower-Ohio 

River Basin are the highest in the country.

LOWER OHIO LOADS

The Lower-Ohio River is made up of the 

Green, Lower-Ohio (also referred to as 

Tradewater River Basin), and Cumberland 

River (GLOC) Basins and some smaller 

basins in southern Indiana. This region has a 

complex environmental setting that is 

affected by various natural processes and 

human activities. The basins in the LowerOhio River region are characterized by karst 

topography (eroded limestone, which creates 

sinkholes, springs, and caves). Land use 

among these basins is primarily agriculture. 

Atrazine, metolachlor, and simazine 

were the most commonly used corn 

herbicides throughout the Lower Ohio 

during 1997 (Kentucky Agricultural 

Statistics Service, 1998) and are the three 

most frequently detected pesticides in the 

Lower-Ohio River Basin (Kelly and others, 

2001). Based on estimated-use data from 

1997 agricultural applications, a total of 

about 600,000 kg (kilograms) of atrazine, 

430,000 kg of metolachlor, and 50,000 kg of 

simazine were applied in the GLOC Basins. 

These estimates were calculated from 

agricultural inputs obtained by multiplying 

the pesticide application rates, the 

percentage of crop receiving pesticide 

application, and the county-level, cropacreage data from the 1997 Census of 

Agriculture (U.S. Department of Commerce, 

website: http://www.nass.usda.gov/census/). 

Pesticide application rates and treatment 

percentages were obtained from a 1997 

survey by the National Center for Food and 

Agriculture Policy (Gianessi and Marcelli, 

2000). Atrazine, metolachlor, and simazine 

are used in urban areas for non-selective 

control of vegetation in rights-of-way; 

however, there are no reliable estimates of 

application amounts. 

Table 2. Estimated mean loads and yields of atrazine, simazine, and metolachlor in the Ohio River Basin, 1997–2000

[Load in metric tons; yield in grams per square kilometer]

Basin

Herbicides

Atrazine Simazine Metolachlor

Load Yield Load Yield Load Yield

Upper-Ohio 7.68 48.2 1.42 8.93 3.82 23.9

Middle-Ohio 22.9 254 3.42 37.8 11.0 122

Wabash 61.2 806 5.16 67.8 25.6 337

Tennessee 6.54 61.7 .838 7.91 1.40 13.2

Lower-Ohio 107 1,120 14.2 148 38.9 406
Atrazine had the highest mean annual 

load from the Lower-Ohio River Basin with 

107 metric tons (table 2); this amount 

represented about 18 percent of the atrazine 

applied to agricultural land in the LowerOhio River Basin. This percentage is much 

higher than earlier estimates of atrazine 

(1.13 percent) transported from the LowerOhio River Basin (Battaglin and others, 

1993). Most literature indicates that losses 

on the order of 1 to 3 percent of the applied 

amount of herbicide can be expected. The 

percentage may increase to 5 or 10 percent 

during catastrophic events, such as a large 

rainfall event, soon after herbicide 

application. The percentage loss of simazine 

and metolachlor were similar to 

atrazine—28 and 9 percent, respectively. 

The large percent losses of atrazine, 

simazine, metolachlor estimated for the 

Lower-Ohio River Basin is unusual and a 

concern, and there is no immediate 

explanation for these losses. Possible 

explanations include unusually large rainfall 

events (there were some in 1997 and 1998), 

unusual agricultural practices or pathways 

for the movement of these herbicides 

(perhaps the karst topography), or 

measurement error. The load of herbicides 

from the Lower-Ohio Basin was not 

measured directly, but was estimated by 

subtracting the load from the Wabash, 

Tennessee, and the Middle-Ohio Basin from 

the load determined at the mouth of the 

Ohio. The difference was attributed to the 

GLOC Basins and the smaller basins in 

southern Indiana. These basins are the only 

other basins that discharge into the Ohio 

River between the two NASQAN Ohio River 

main stem sites (fig. 1, map numbers 2 and 

5). It should be noted that the load from the 

Tennessee River at Highway 60 near 

Paducah, Ky., site is probably low because of 

the diversion of water to the Cumberland 

River. Little information is available on the 

occurrence of herbicides in the streams of 

these basins; therefore, there is a need for 

measuring the load directly. In 2001, the 

NASQAN program redirected some 

resources to begin directly monitoring the 

Cumberland River and also established a 

sampling site on the Ohio River near 

Pittsburgh to further define the load of 

material from the Upper-Ohio River Basin.

Figure 2. Atrazine yield from National Stream Quality Accounting Network (NASQAN) subbasins, 

1997–2000.

Agricultural land use in the Lower-Ohio River Basin near Leavenworth, Indiana.
REPRESENTATIVE SAMPLING

The spatial variability of a constituent in 

a stream cross section is dependent upon a 

number of factors. If the constituent is in the 

dissolved phase, its distribution in the stream 

cross section depends upon how well mixed 

the stream is and the location of the source of 

entry of the constituent to the stream. If the 

constituent is associated with the particulate 

phase, in addition to the factors affecting 

constituents in the dissolved phase, there 

also is the vertical distribution caused by 

sinking of the particulate matter. This 

distribution has implications for the 

calculation of the constituent load. If the 

constituent concentration changes in the 

stream either horizontally or vertically, or 

both, then where and how the sample is 

collected will affect the concentration used 

to calculate the load.

The collection of a representative 

sample from the Ohio River near its 

confluence with the Mississippi River can be 

difficult (fig. 3). The concentration of 

constituents can vary considerably across the 

stream as the Cumberland and Tennessee 

Rivers enter the Ohio River from the south, 

and the Wabash River enters from the north 

above the sampling site. The water quality of 

the Wabash River reflects its intensive 

agricultural land use, whereas the Tennessee 

and Cumberland Rivers have more forest 

land use. This can be seen in the 

concentration of metolachlor in the Ohio 

River during July 1999 (figs. 3 and 4). The 

concentration of metolachlor in the stream 

nearly doubles from the south side of the 

river to the north side. These data were 

collected in July 1999 in an experiment to 

determine if representative samples were 

being collected on the Ohio River. Other 

herbicides show the same pattern and some 

the reverse (tebuthiuron), with high 

concentrations on the Kentucky side of the 

Ohio River. 

In order to ensure that a representative 

sample is collected, the NASQAN program 

collects all of its water samples using depthand width-integrating techniques and uses 

isokinetic (the velocity of the water into the 

sample bottle is the same as the velocity of 

the stream) sampling equipment.

REFERENCES CITED

Battaglin, W.A., Goolsby, D.A., and Coupe, R.H., 

1993, Occurrence and annual transport of 

agricultural chemicals in the Mississippi 

River, 1991-92, in Goolsby, D.A. and others, 

eds., Selected papers on agricultural 

chemicals in water resources of the 

Midcontinental United States: U.S. 

Geological Survey Open-File Report 93-418, 

p. 26-38.

Edwards, T.K., and Glysson, G.D., 1988, Field 

methods for measurement of fluvial 

sediment: U.S. Geological Survey Open-File 

Report 86-531, 120 p.

Gianessi, L.P, and Marcelli, M.R., 2000, Pesticide 

use in U.S. crop production 1997: 

Washington D.C., National Summary Report, 

National Center for Food and Agricultural 

Policy [variously paged].

Hooper, R.P., Aulenbach, B.T., and Kelly, V.J., 

2001, The National Stream Quality 

Accounting Network—A flux-based 

approach to monitoring the water quality of 

large rivers: Hydrologic Processes, v. 15, 

p. 1251-1269.

Kelly, V.J., Hooper, R.P., Aulenbach, B.T., and 

Janet, Mary, 2001, Concentrations and annual 

fluxes for selected water-quality constituents 

from the USGS National Stream Quality 

Accounting Network (NASQAN), 1996-

2000: U.S. Geological Survey WaterResources Investigations Report 01-4255, on 

line at <URL: http://water.usgs.gov/nasqan/

progdocs/wrir/index.htm>, accessed 

November 26, 2001. 

Kentucky Agricultural Statistics Service, 1998, 

Kentucky agricultural statistics 1997-1998: 

Louisville, Ky., 144 p.

Kentucky Natural Resources and Environmental 

Protection Cabinet, 2000, Pesticides in 

Kentucky Rivers: Frankfort, Ky., Division of 

Water, 89 p.

Ohio River Valley Water Sanitation Commission, 

1997, Herbicides in the Lower Ohio River 

Basin: Cincinnati, Ohio, 43 p.

Shelton, L.R., 1994, Field guide for collecting and 

processing stream-water samples for the 

National Water-Quality Assessment 

Program: U.S. Geological Survey Open-File 

Report 94-455, 42 p.

U.S. Department of Agriculture, 1997 census of 

agriculture, geographic area series, v. 1, 

U.S. summary and county level data: 

Washington, D.C., on line at 

<URL: http://www.nass.usda.gov/census/>, 

accessed December 11, 2001.

— Angela S. Crain

For more information contact:

NASQAN Mississippi River Basin Coordinator

308 South Airport Road

Pearl, MS 39208-6649

e-mail: rhcoupe@usgs.gov

URL: http://water.usgs.gov/nasqan

Printed on recycled paper

Figure 3. Schematic of the cross section of stream sampling on 

the Ohio River below Paducah, Kentucky.

Figure 4. Cross-sectional variability of 

metolachlor concentrations during July 

1999 in the Ohio River near Grand Chain, 

Illinois (map number 5).

U.S. Geological Survey personnel collecting 

water-quality samples on the Ohio River at 

Cannelton Dam, Kentucky (map number 2).