U.S. Department of the InteriorU.S. Geological Survey

Charles G. Crawford and Robert J. Gilliom

National Water-Quality Assessment Program

Pesticide National Synthesis Project

Estimating pesticide concentrations in U.S. streams from watershed characteristics and pesticide properties: WAtershed Regressions for Pesticides (WARP)

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Too few available monitoring data to meet need

Prohibitively expensive to sample everywhere

What is WARP?

WARP relates pesticide concentrations in streams to watershed characteristics using an empirical regression approach

Independent models are developed for selected concentration percentiles

Why do we need WARP?

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POTENTIAL PREDICTORS: Explanatory Variables Evaluated

Pesticide Use

Physical Basin Characteristics

Other Basin Characteristics

Agricultural Management Practices

Soil Properties (STATSGO)

Hydrologic Parameters

Weather/Climate

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In the WARP models atrazine concentration is a function of:

(+) atrazine use intensity (use per unit area),

(+) rainfall erosivity factor from Universal Soil Loss Equation (USLE),

(+) soil erodibility factor from USLE,

(+) area of drainage basin,

(-) percentage of total stream flow derived from Dunne overland flow

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Watershed characteristics help us predict pesticideconcentrations in streams

NO MODEL

0.0001

0.01

1.0

100.0R-square = 0.00

MODEL WITH ONLY USE INTENSITY

0.0001

0.01

1.0

100.0R-square = 0.59

FULL MODEL

0.0001

0.01

1.0

100.0

0.0001 0.001 0.01 0.1 1.0 10.0 100.0

R-square = 0.73

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PREDICTED ATRAZINE CONCENTRATION

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By combining models for the nine percentiles we can predict the annual distribution of pesticide concentrations

Concentrationexceeded

for 21 days

Concentrationexceeded

for 60 days

0.01 0.1 1 100

20

40

60

80

100

CU

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IVE

PE

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(PE

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IS E

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ATRAZINE CONCENTRATION

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36 pesticides were used to extend atrazine models for use with multiple pesticides

Surface and Foliar Applied HerbicidesAcetochlor Metolachlor

Acifluorfen Metribuzin

Alachlor Nicosulfuron

Bentazon Norflurazon

Bromoxynil Oryzalin

Chlorimuron ethyl Pronamide

Cyanazine Propachlor

Fluometuron Terbacil

Linuron

Insecticides and FungicidesBenomyl Oxamyl

CarbofuranPhorate

Ethoprop Propargite

FonofosPropiconazole

Methomyl Terbufos

Methyl parathion

Incorporated HerbicidesButylate Pebulate

EPTC Triallate

EthalfluralinTrifluralin

Herbicides applied to paddysPropanil Thiobencarb

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The WARP atrazine models are adjusted for multiple pesticides by

a factor based on the Surface Water Mobility Index (SWMI)

a factor based on vapor pressure

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USES: National extrapolation

Estimate exposure in streams

Guide monitoring design

Identifying at risk populations

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Predicted 95th percentile carbofuran concentration

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Probability that 95th percentile chlorpyrifos concentration exceeds 4-day moving average ambient water-quality criteria for aquatic life

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Predicted annual mean atrazine concentrations

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WARP model limitations

Existing WARP models are for flowing waters only (not reservoirs)

We can only predict where we have delineated watersheds

No co-occurrence of multiple pesticides

Can’t incorporate factors for which there are no data (i.e. buffer strips)

Can’t address factors that significantly change the relationships underlying WARP models without new data

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Summary

Statistical models have been developed to predict pesticide concentrations at unmonitored streams

These models allow us to extrapolate our limited monitoring data to unmonitored locations so we can:

• Estimate pesticide exposure in streams

• Identify areas of concern for future monitoring

• Identify populations where pesticide exposure through source waters may be of concern

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For more information:

USGS NAWQA program:

http://water.usgs.gov/nawqa/

NAWQA pesticide national synthesis project:

http://ca.water.usgs.gov/pnsp/

WARP atrazine models:

http://pubs.usgs.gov/wri/wri034047/