Chapter 18
Field and Model Estimates of Pesticide Runoff from Turfgrass 1
2
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W. D. Rosenthal and B. W. Hipp 1
Texas Agricultural Experiment Station, Temple, TX 76502 Texas Agricultural Experiment Station, Dallas, TX 75252 2
Environmental awareness of surface runoff water quality is increasing. A study was conducted to analyze the impact of different turfgrass fertilizer and pesticide management systems on runoff water quality. A hydrologic and water quality model, Erosion Productivity Impact Calculator (EPIC), was used to estimate pesticide and nutrient concentrations in runoff from turfgrass on a Houston Black Clay. Nutrient and pesticide concentrations in the surface runoff increased significantly for highly maintained turfgrass systems. A larger fraction of the amount applied was observed in runoff for the moderate application rate treatments. Simulated results are being validated from measured runoff of turfgrass plots at Dallas, TX.
Pesticide and nutrient pollution in surface runoff from urban landscapes is becoming an increasingly important environmental issue. There has been an increase in the number of reports of urban surface runoff with detectable levels of pesticides and nutrients (7). Highly maintained turfgrass areas, as found on golf courses, may have surface runoff with detectable amounts of pollutants (2). In addition, common rules associated with fertilizing lawns (e.g. watering immediately after fertilizer application) may in fact be detrimental to runoff water quality. As a result, management practices to reduce surface runoff nutrient and pesticide concentrations need to be evaluated. Two ways to evaluate management practices are monitoring and simulation modeling. Numerous research projects have been conducted evaluating the effect of urban cultural practices on surface water quality (5,4). Evaluations of different management treatments through monitoring will take time and money. In addition, several models (e.g. SWRRBWQ, EPIC, QUAL-TX) have been developed to simulate surface water quality for extreme events (5). However, a combination of monitoring and modeling has not been used to evaluate management practices in different soil and climatic environments. Our objective was to (I) develop and monitor surface runoff water qualityfromturfgrass plots subjected to different management levels, and (2) simulate extreme runoff conditions for the above management scenarios. The EPIC (Erosion Productivity Impact Calculator) 0097-6156/93/0522-0208$06.00/0 © 1993 American Chemical Society
Racke and Leslie; Pesticides in Urban Environments ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
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ROSENTHAL & HIPP
209 Estimates of Pesticide Runoff from Turfgrass
model was developed to monitor erosionfromplots and small fields. This model was selected because it can simulate the fate of many pesticides simultaneously and quantify runoff magnitude for small areas.
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MATERIALS AND METHODS Model Description. A detailed description of the EPIC model and its capabilities was given by Williams et al. (5, 6). The model simulates hydrologie processes, plant growth, and pesticide/nutrient fate based on tillage, environment, and other management practices. The pesticide fate components were recently incorporated from the GLEAMS model (7). A mass balance approach accounts for pesticide fate. Key pesticide inputs into EPIC include pesticide name, application date and rate, effective killing efficiency, adsorption coefficient for organic carbon, half-life in the soil and foliage, water solubility, and washoff fraction. Pesticide fate output information includes pesticide quantities in surface runoff, adsorbed to the plants and each soil layer, degraded on the plant and in the soil, leaching out of the root zone, and lost in eroded sediment. The amount and concentration in surface runoff is primarily a function of the half-life of the pesticide, soil adsorption, chemical characteristics, chemical placement, and application amount Turfgrass Plot Description. Twenty-four 2.5 X 3.7 m turfgrass plots were installed in 1990 at the Texas Agricultural Experiment Station in Dallas. Four management treatments were imposed on the plots and replicated six times. These included a highly maintained, medium-high maintenance, medium-low maintenance, and xeriscape (low) maintenance systems (Table I). Ornamental plants with a bark mulch surface were installed on 1/3 of the area in each plot. Bermudagrass (Cynodon dactylon) was planted in the medium and highly maintained treatments; whereas, Buffalograss (Buchloe dactyloides) was planted in the low maintenance plots. The plots were mowed every 7-14 days. Each plot was on a 2% slope of Houston Black clay soil and fitted with gutters on the downslope side that funnelled runoff water to collection samplers. Water quality could be monitored through periodic sampling during a runoff event. The amounts of chemicals applied to the plots for each treatment are given in Table I and are representative of common practices on turfgrass. Surface runoff was collected and sampled for N0 " and PO4 , but Diazinon (Spectracide), which was applied once in 1991, was not analyzed in the surface runoff. 2
3
Model Simulation. The same four treatments and nutrient and pesticide application amounts and dates were simulated using the EPIC model (Table I). Additional insecticides and pesticides were simulated. Application dates and amounts were inputs into the model (Table II). The model was run under one scenario: using the model weather generator to simulate 30 years of representative weather data for Dallas, TX. Other inputs were representative of soil, plant, and atmospheric conditions for Dallas, TX. RESULTS Field. Nitrate concentrations were significantly different for the various treatments. Surface runoff from early irrigations had higher NO3" concentrations in the runoff than later irrigations. Irrigations on the same day as fertilizer applications on 3 June had
Racke and Leslie; Pesticides in Urban Environments ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
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PESTICIDES IN URBAN ENVIRONMENTS
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Table I. Experimental Design of Turfgrass Runoff Study Treatment Low
Medium-Low
Medium-High
High
Maintenance
Maintenance
Maintenance
Maintenance
150
250
975
73
145
290
Irrig. (mm) Fertilizer (kg/ha) # Fertilizer App. Insecticides
None
(kg/ha)
Chlorpyrifos (2.2) or Carbaryl (1.1) or
Chlorpyrifos or
Chlorpyrifos or
Carbaryl (1.1) or
Carbaryl (1.1) or
Diazinon (6.0) # Insecticide App. Herbicides (kg/ha)
None
Diazinon (6.0)
Diazinon (6.0)
1
1
None
2,4-D (1)
2,4-D (1)
or
or
Dicamba (.5)
Dicamba (.5)
or
or
Atrazine (1.5)
Atrazine (1.5)
1
1
# Herbicide App.
Table II. Peak Diazinon Concentrations (ppb) for May-October Treatment
May
June
July
August
September
October
High
102
40
70
3
4
3
Medium High
400
335
60
5
3
2
Medium Low
400
390
72
16
12
0.7
Racke and Leslie; Pesticides in Urban Environments ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
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Estimates of Pesticide Runofffrom Turfgrass
average ΝΟ3· levels of 15-16 ppm for the highly and medium high maintained treatments, which is above the recommended EPA threshold level. Subsequent irrigations had decreasing NO3" levels (Figure 1). Another scenario was to determine the nitrogen concentration in a runoff producing storm late in the growing season. On 22 October 1991, ten cm of water was applied to all plots. The mean runoff for the highly maintained treatment was 2.47 cm; the low maintenance treatment had only 0.25 cm of runoff (LSD.o5=1.5 cm). Concentrations of nitrate in the runoff were 5 ppm for the highly maintained treatment and 0.3 ppm for the low maintenance treatment. Additional runoff had lower NO3' concentrations in runoff for the highly maintained treatment. The low maintenance treatment had a consistent 0.3-0.4 ppm NO3- (LSD.o5=2.2 ppm) concentration in the runoff throughout these irrigations (Figure 1). This level represents background Ν concentrations in the surface soil layer and organic matter. These were the only two runoff events during 1991. Model. Nitrogen and pesticide concentrations were highest for the highly maintained and medium-high treatment (Tables II, III). These values were significantly higher for precipitation amounts immediately after application. Concentrations for medium low treatments were even greater than the high and medium high treatments. Of the six pesticides analyzed, atrazine and diazinon had the longest continuous period with concentrations above the EPA Lifetime Health Advisory Level (Diazinon~0.6 ppb; Atrazine 3 ppb). Atrazine had a maximum surface runoff concentration of 919 ppb; diazinon concentrations in surface runoff were as high as 400 ppb. Ranges of monthly quantities of atrazine and diazinon were 1 to 47 g ha and 1 to 26 g ha , respectively. Monthly nitrate levels averaged 1 ppm to 390 ppm for the highly and low maintained treatments (Table ΠΙ). These results contradict those of Watschke (2). He found that the concentration of pesticides did not exceed the EPA threshold the majority of the time. The difference could be explained by the differences in soil type. Watschke (2) used sand as the soil medium. In the present study, the soil was Houston Black clay, which has a slow infiltration rate (0.1 cm hr ). With the slower infiltration rate, measurable surface runoff is more likely to occur. 1
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1
DISCUSSION In spite of the fact that simulated results indicate there may be occasions when nutrient and pesticide concentrations in surface runoff from a single lawn exceed the EPA threshold level, the combined water concentration within the urban system may be diluted to the point of having combined concentrations less than the threshold. The EPA found that pesticides and nutrients were present in urban runoff, but were not as prominent as metals such as lead (1). Further studies are needed using other pesticides to determine the degree of dilution and fate in the urban system. Additional studies with the turfgrass plots will be conducted in the future. Volatilization of the pesticide is one factor not accounted for in EPIC. Thatch may also serve as an adsorption medium for the pesticide. This may account for some quantity of pesticide lost for these pesticides.
Racke and Leslie; Pesticides in Urban Environments ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
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212
PESTICIDES
IN URBAN
ENVIRONMENTS
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Nitrogen Concentration (ppm) Ε
α Δ
5
• Δ
CL CL C Ο
2?
3
c
•
s
-
Δ
CD ο Ο
Ο
ϋ Ζ
1
* I 0.5
9
* I 1
I
1.5
Ο ι 2
2.5
Accumulated Runoff (cm) High •
Med. High Δ
Med. Low Ο
Low *
Runoff from 10 cm irrigation
Figure 1. Nitrogen concentration as a function of accumulated surface runoff from the turfgrass plots at Dallas.
Table III. Peak Nitrate Concentration (ppb) in Runoff Treatment
January February March April May June July August September October November December
High
Medium High
Medium Low
Low
18 19 14 142 226 63 70 137 44 9 5 10
2 13 9 131 18 59 14 276 1 1 3 5
1 8 8 3 88 39 309 11 636 1 2 3
1 5 6 2 4 4 2 1 1 1 1 2
Racke and Leslie; Pesticides in Urban Environments ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
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Estimates of Pesticide RunofffromTurfgrass 213
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LITERATURE CITED 1. U. S. Environmental Protection Agency. 1983. Final Report of the Nationwide Urban Runoff Program. 2. Watschke, T. L., S. Harrison, and G. W. Hamilton. USDA Green Section Record. 1989, (May/June), 5-8. 3. Morton, T. G. A. J. Gold, and W. M . Sullivan. J. Environ. Qual. 1988, 17, 124-130. 4. Petrovic, A. M . J. Env. Qualit. 1990, 19, 1-14. 5. Williams, J. R., C. A. Jones, and P. T. Dyke. Trans. ASAE. 1984, 27, 129-144. 6. Williams, J. R., C. A. Jones J. R. Kiniry, and D. A. Spanel. Trans. ASAE. 1989, 32, 497-511. 7. Leonard, R. Α., W. G. Knisel, and D. A. Still. Trans. ASAE. 1987, 30, 1403-1418. RECEIVED
October 30,
1992
Racke and Leslie; Pesticides in Urban Environments ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
