United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30613
Research and Development
EPA-600/S3-82-032 Sept. 1982
Project Summary
Field-to-Stream Transport of
Agricultural Chemicals and
Sediment in an Bowa
Watershed: Part I. Data
Base for Model Testing
(1976-1978)
H. P. Johnson and J. L. Baker
Data on the field-to-stream transport
of sediment and chemicals from an
agricultural watershed were collected
in a three-year study to provide
information for testing and evaluating
mathematical models under develop-
ment for predicting agricultural non-
point source pollution. These models
are prepared as tools to evaluate the
effectiveness of different farm man-
agement practices in controlling
losses of nutrients, pesticides, and
sediment in field drainage to receiving
waters. In the study, data were
collected for small corn, soybean, and
pasture fields; for two larger mixed-
cover watersheds; and at three drain-
age-stream sites.
During the study (1976-1978),
annual rainfall (753 mm) and stream-
flow (124 mm) averaged a little below
normal. Sediment losses were also
low because of a lack of intense rains,
averaging 2.6 t/ha from row-crops
and 0.9 t/ha from the watershed as a
whole. Soluble chemical losses (NH4-
N, NO3-IM, PO<-P, Cl and TDS) in
surface runoff were less than that
deposited with rainfall. Because IMO3-
N, Cl and TDS were concentrated in
subsurface drainage, losses from the
watershed as a whole due to stream-
flow (surface plus subsurface drainage)
were significantly larger than losses
from surface runoff alone.
Average annual pesticide losses
from the field were least for the
shortest-lived herbicide (0.2% of that
applied) and greatest for the most
persistent (1.6%). No runoff event
occurred within a week of application.
On the basis of percentage applied,
losses or export from the watershed as
a whole were about 25% of the losses
from the two individual fields studied.
With the exception of the strongly
adsorbed paraquat, at least 80% of the
losses occurred in the water phase as
opposed to that adsorbed on sediment.
This Project Summary was developed
by EPA's Environmental Research
Laboratory. Athens. GA, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
Concern about potential pollution
from agricultural land drainage and
associated land erosion has increased
due to some recent trends in agriculture.
Increases in intensive row-crop farming,
higher fertilizer application rates, and
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larger areas treated with pesticides tend
to increase the nonpoint source pollution
potential. Other trends, however, such
as increasing use of conservation tillage
and less persistent pesticides, should
reduce the pollution potential from
agricultural lands.
During the past decade, environ-
mental scientists and engineers have
accepted simulation modeling as a
technique for predicting effects of
weather and management changes on
the quality of agricultural drainage
water. Using relatively limited site-
specific information, simulation models
can provide required water quality
management information, for the con-
trol of nonpoint pollution in a specific
watershed. These models, however,
must be calibrated and verified using
data from carefully monitored water-
sheds. Although some water flow and
quality data are often available from
either small areas, e.g., plots, or large
river systems, comprehensive data sets
that define areal and temporal changes
from the field to the stream are rare.
The primary objective of the study
summarized here was to collect data on
stream hydrology and on sediment,
nutrient, and pesticide transport from
field to stream for intensively cropped
agricultural watersheds, ranging in size
from a few hectares to about 50 km2,
and at the same time provide additional
understanding of the physical and
chemical processes occurring that
influence chemical losses.
The study area was located in the
Dipper portion of the Four Mile Creek
watershed in northwest Tama County,
Iowa (Figure 1). Data were collected for
the crop years 1976 to 1978, for small (5
to 6 ha) pasture, corn and soybean
fields, for two larger mixed-cover
watersheds, and at three stream stations.
Soil profile sampling on the three fields
was performed to determine the amounts
(concentrations) and location (depth of
migration) of nutrients and pesticides as
a function of time.
Results
Table 1 presents a summary of
inventory data for the Four Mile Creek
watershed for the three years of the
study and includes data from a previous
study (1970) for comparison. It is
obvious that the watershed was being
more intensively farmed during this
later study, with 55% of the area m corn
and 22% in soybeans, with nearly all the
row-crops receiving herbicides. In
addition, 73% and 97% of the corn was
A Gaging Station
• Rain Guage Location
•°- Weather Station
Field
Site 2
Figure 1. Four Mile Creek watershed instrumentation.
Table 1. Four Mile Creek Watershed Inventory
1970
1976
1977
1978
Corn (% area )
fertilized (%)
N (kg/ ha)
P205 (kg/ ha)
herbicide (%)
insecticide (%)
Soybeans (% area)
fertilized (%)
P20s (kg/ha)
herbicide (%)
40
87
115
59
71
54
17
10
69
75
55
98
159
55
99
58
20
12
49
94
54
97
166
62
98
80
24
24
58
95
55
97
174
57
98
80
22
14
55
97
the pasture, which averaged 9 mm/yr of
treated with insecticides and fertilizer,
respectively. Nine herbicides accounted
for over 95% (by mass) of the herbicide
used; five insecticides accounted for
over 98% of the insecticides. About 1%
of the watershed was terraced; a few
farmers used conservation tillage,
contouring and strip-cropping. Table 2
presents a summary of precipitation,
flow, sediment and soluble chemical
data. Precipitation during the study
averaged 92% of normal; in one 12-
month period, the study area received
only 56% of the average annual precipi-
tation. Average annual stream-flow
from the whole watershed was 124
mm, 26 mm below the long term
average of about 150 mm. Surface
runoff from the two, small, row-cropped
fields averaged 36 mm, of which over 50
was snowmelt The same was found for
surface runoff. Annual sediment yield
from the pasture, soybean and corn
fields averaged 0.03, 1.3 and 4.5 t/ha,
respectively. Sediment loss or export
from the whole watershed of 50 km2,
averaged 0.9 t/ha. No really severe
storms occurred during the study
period.
In general, concentrations of NH4-N
and PC>4-P were higher in surface runoff
water than in subsurface drainage; the
reverse was found for N03-N, Cl and
TDS. Average surface runoff losses
from pasture, corn, and soybean fields
of all dissolved chemicals were less than
the amounts deposited by precipitation.
The amounts of NOa-N, Cl, and TDS lost
annually with the streamflow which
included shallow subsurface drainage
and base flow as well as surface runoff,
were equal to or greater than the
amounts deposited in precipitation
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Table 2.
Nutrients and Sediment in Precipitation, Surface Runoff. Tile, and Creek Flow
Precip.
Year
1976
1977
1978
Amount
mm
554
828
878
NHA-N
ppm kg/ha
.78
.87
.78
4.20
7.20
6.85
NOyN
ppm kg/ha
0.8
1.0
0.8
4.1
8.3
6.8
P04-P
ppm kg/ha
.054
.028
.063
.290
.230
550
Cl
ppm kg/ha
1.5
1.5
2.0
8.2
12.5
17.6
TDS Sediment
ppm kg/ha ppm kg/ha
33
51
50
179 — —
420 — —
439 — —
Runoff
Corn:
Site 2
Site 1
Site 2
1976
1977
1978
51.3
11.9"
47.3
.42
2.66
.43
.22
.32
.20
5.3
0.7
3.0
2.7
01
14
.047
.819
.112
024
097
.053
2.1
7.6
1 7
1.1
0.9
0.8
165
134
58
85
16
27
10210 5387
43373 5558
5173 2488
Soybeans:
Site 1
Site 2
Site 1
1976
1977
1978
58.6
0.9
46.4
.09
.06
.24
.05
.11
3.5
0.2
1.7
2.1
0.8
.029
046
.349
.017
<001
.162
7.3
0.9
8.0
43
<0 1
37
134
83
80
78
1
37
4739
20457
1869
2779
180
867
Pasture:
Site 3
1976
1977
1978
13.1
6.1
.20
.62
.54
.03
.05
.03
0.8
04
05
0.1
1 154
898
1.051
.151
.078
.064
4.0
1.7
3.2
0.5
0.1
02
133
56
89
17
5
5
305
312
79
40
27
5
Tile drainage
Intra basin
Site 7§
284 ha
Site 8§
149 ha
1976
1977
1978
7376
7377
7S7S
7376
7377
7375
6.7
2.6
32.7
89
9.2
42.0
.11
.13
.10
.02
1 00
.22
.71
.32
.02
.30
10.2
14.0
13.4
0.5
3.0
<0.1
1.0
.069
.116
.102
.173
1.361
.004
.437
0.9 <0.1
3.7 1.5
.174 .016
.570 .240
144
20.2
17.9
3.6
90
2.3
10.0
0.1
2.9
0.2
4.2
330
352
312
108
148
68
115
3
47
6
48
992
585
7966
2029
26
188
736
852
Creek
Site 6§
345 ha
Site 5§
3575 ha
Site 4
5055 ha
1976
1977
1978
1976
1977
1978
1976
1977
1978
13.1
69.9
250.5
13.5
52.1
203.5
122.7
43.6
197.4
.02
.14
.15
.02
.40
.38
24
.23
.37
<01
.10
.38
<01
.21
.77
.29
.10
.74
5.8
11.2
11.3
5.8
11.6
12.5
7.9
10.0
11.0
0.8
7.8
28.3
0.8
6.1
255
9.7
4.4
21.6
.029
.201
149
.027
.299
.161
066
.114
.107
.004
.141
.374
004
.156
.328
.081
050
.212
11.0
12.0
13.2
179
23.1
17.1
12.1
17.3
15.3
1.4
84
33.0
2.4
12.1
34.7
148
7.6
30.1
317
306
280
349
434
308
277
330
278
42
214
703
47
226
627
333
144
549
59
602
793
52
182
793
1274
171
509
8
421
1988
7
95
1614
1564
74
1004
*40% of this runoff occurred within 24 h of fertilizer application and incorporation.
t-4 very localized rain caused 98% of this runoff.
§0nly one sample taken on sites 7 and 8; limited number on sites 5 and 6 since flow monitoring began 5/29/76 for these sites.
(particularly greater for NOa-N). The
amounts of NH4-N and PO4-P lost with
the annual stream flow were still less
than the amounts deposited with
precipitation. Concentrations of N and P
associated with sediment were some-
what dependent on the concentrations
of sediment in runoff; the higher the
sediment concentration, the lower the
nutrient concentration in the sediment.
On average, about 2 kg of N and 1 kg of P
were lost per tonne of sediment
The herbicides alachlor, metribuzin,
and paraquat were soil applied without
incorporation at planting to the soybean
field. Similarly, propachlor, cyanazine
and paraquat were applied to the corn
field. Spray, filter paper, and soil tests
were run to determine the amounts
actually applied. At no time during the
three-year study did a runoff event
occur within one week of application,
and therefore, runoff losses were low
As shown in Table 3, losses ranged from
0% to 3.2% of the herbicide applied The
least losses occurred with the shortest-
lived herbicide, propachlor; the greatest
losses occurred with the longest-lived
herbicide, paraquat Soil core samples
taken during the growing season, in
addition to providing information on
persistence, showed that the pesticides
essentially remained in the top 7.5 cm of
the soil With the exception of the
strongly adsorbed herbicide, paraquat,
over 80% of the herbicide runoff losses
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Table3.
Year
1976
1977
1978
Percentage of Applied Herbicides Lost
Site Alachlor Metribuzin
field
4 mi watershed
field
4 mi watershed
field
4 mi watershed
0.5
0.1
0.0
0.0
0.3
0.1
0.7
0.1
0.0
0.0
04
0.1
Propachlor
0.2
0 1
0.0
0.0
0.3
0.1
Cyanaz/ne
1.0
0.1
0.005
0.0
0.8
0 1
Atrazine
_
0.2
0.0
0.0
0.3
Paraquat
3.2
1.0
02
00
1.4
0.1
occurred in the solution phase. Losses
of the herbicides with streamflowfrom
the whole watershed, on a percentage
of applied basis, were about 25% of the
edge-of-field losses.
Stream cross sectional areas were
measured at several pointstodetermine
what portion of the total sediment load
could be attributed to bank erosion
and/or channel degradation Compari-
son to areas measured in a previous
study indicated that about 25% of the
sediment transported from the water-
shed came from the channel.
Conclusions
• Snowmelt can be a significant
portion of annual surface runoff
(averaged about 50%).
• Recent tillage is an important
factor affecting rainfall-runoff
amounts.
• Good rainfall distribution data,
areally and with time, are critical to
runoff modeling.
• Rainfall-runoff and sediment losses
from grassland are very low (sedi-
ment yield was less than 50 kg/ha
yr'1).
• For row-cropped watersheds, sedi-
ment sizes and concentrations in
runoff increase with rainfall inten-
sity.
• On a relative basis, sediment size
was coarsest in runoff directlyfrom
the field and finest after passage
through a good grassed waterway.
• Streambank erosion can account
fora significant portion of sediment
yield from the watershed (up to
25%).
• Soluble nutrient amounts deposited
in precipitation are significant (and
in this study are larger than)
relative to losses in surface runoff.
• Significant portions of NH4-N and
PO-t-P losses can occur with snow-
melt (in one year 75%).
• Annual NO3-N losses, associated
primarily with subsurface drainage,
can be significant (up to 22 kg/ha).
• Concentrations of PO4-P can exceed
1.0 ppm in runoff where animal
wastes, decaying vegetation and P
fertilizer are deposited on the soil
surface
Nutrient losses associated with
sediment usually exceed those
associated with water.
Pesticide losses are usually less
than 1% of that applied if a runoff
event does not occur within one
week of application.
With the exception of very strongly
adsorbed pesticides, the great bulk
of pesticide loss takes place in
solution
The limited data indicate a signifi-
cant attenuation of losses between
field and stream.
Work on methods of chemical
application to improve efficiency of
use and to decrease losses to
surface waters is needed
Means to implement improved
agronomic management practices
relative to chemical use (amount
and timing) and their application
methods need to be devised (similar
to the means of implementation of
soil conservation practices)
H. P. Johnson andJ. L. Baker are with Iowa State University, Ames, IA 50011.
Charles N. Smith is the EPA Project Officer (see below).
The complete report, entitled "Field-to-Stream Transport of Agricultural
Chemicals and Sediment in an Iowa Watershed. Part I: Data Base for Model
Testing (1976-1978)," (Order No. PB 82-254 046; Cost: $40.50. subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
College Station Road
Athens, GA 3O613
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Information
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