Robert N. Lerch

Combining Long-Term Monitoring with Identification of Vulnerable Areas in

Restrictive Layer WatershedsRobert N. Lerch

Soil Scientist,USDA-ARS Cropping Systems & Water Quality Research

Unit, Columbia, MOARS Scientists: E. E. Alberts, C. Baffaut, W. W. Donald, F. Ghidey, A. T. Hjelmfelt, N. R. Kitchen, E. J. Sadler, K. A. Sudduth

Collaborators: P. E. Blanchard, Univ. of Missouri; M. L. Bernards, Univ. of NebraskaP. J. Shea, Univ. of Nebraska; M. Milner, Univ. of Nebraska

• Data Sources: multi-scale approach to monitoring herbicide transport– Regional: Northern Missouri/southern Iowa region (1997-1999)– Basin: Salt River Basin (2005-2010)– Watershed: Goodwater Creek Experimental Watershed (GCEW)

(1992-present)

• Identifying vulnerability in space and time– Direct Observation

Areal herbicide loss rates on a mass per treated area basis– Temporal Index

Development of a cumulative vulnerability index (CVI) for annual atrazine loads

– Process-Based Index Model Predicting the risk of pesticide transport temporally and spatially

Presentation Overview

Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO

• Grab samples were collected at 21 USGS hydrologic monitoring stations between April 15 and July 15 from 1997 to 1999.

• Watershed areas ranged from 210 to 18,000 km2; total area ~56,700 km2

• Samples were analyzed for 6 commonly used corn and soybean herbicides: acetochlor, alachlor, atrazine, cyanazine, metolachlor, and metribuzin; and 4 triazine metabolites: cyanazine amide (CYAM), deethylatrazine (DEA), deisopropylatrazine (DIA), and hydroxyatrazine (HA).

• Herbicide loads computed using linear interpolation of concentration data multiplied by daily discharge.


Regional-Scale Monitoring

Load Calculations Linear Interpolation

Con

cent

ratio

n ( g

/L)

0.1

1

10

100D

isch

arge

(m3 /s

)

0

50

100

150AtrazineDischarge

Date (month/day)


Land Use

Row Crops • Row crop intensity

ranged from 22% to 77% of the watershed areas from 1997-99

• Corn, soybeans, and sorghum account for essentially all row crop production in the region


Watershed VulnerabilityWatershed Vulnerability = ArealLoss on a Treated Area Basis*

*Average sum of 6 herbicides and 4 metabolites for 1997 to 1999

Hydrologic Soil Groups C and D


Herbicide Contribution to the Missouri and Mississippi Rivers

*Average of 1997-99

WatershedDrainage

Area Discharge ATR CYN ACET ALA METOL METR

-------------------- % of Missouri River at Hermann, MO ------------------------

MO River Tributaries 3.1 14.2* 38 37 30 12 21 55

--------------------- % of Mississippi River at Grafton, IL -----------------------

MS River Tributaries 3.4 3.2 7.4 9.1 2.3 7.5 5.4 40



Extent of Claypan Soils

Claypan Soils

Goodwater Creek Watershed

Salt RiverBasin

Major Land Resource Area 113Central Claypan Areas

33,000 km2 in MO and IL

Claypan Characteristics• Smectitic mineralogy (high shrink-swell

clays)• Near surface feature; top 1m of soil profile

• Very low saturated hydraulic conductivity (Ksat ~1 m/s)


Basin-Scale Monitoring• Salt River Basin

– ~6,500 km2 in area– Mark Twain Lake is major public water supply in

the region Serves ~42,000 people EPA 303(d) list for Atrazine until 2003

• 13 Sites Monitored from 2005-2011– Automated samplers for runoff events– Supplemental grab samples following events and

under baseflow– Discharge data from 10 USGS gauged sites– Rating curves to developed at 3 sites

• Measurements: – Discharge– Rainfall– Herbicides (atrazine, acetochlor, metolachlor,

metribuzin, selected atrazine metabolites)– Nutrients (total and dissolved N and P)– Sediment

Missouri

Salt R. Basin

Salt River Basin

Monitored Area

• Monitoring encompasses ~4,600 km2 (71%) of the Salt River basin.

• Individual watershed areas monitored represent 63 to 94% of the entire watershed areas.

Land-UseIn general, the larger watersheds (North, Middle, Elk and South Forks) have more grassland and forested areas and less cropland than the smaller watersheds

(44%)(33%)

(18%)

Watershed-Scale MonitoringGoodwater Creek Experimental Watershed (GCEW)

• Drainage area - 77 km2

72 km2 monitored 1st – 3rd order streams

• Flat to gently rolling topography (1-3% slopes)

• Claypan soilsRestrictive layer generally within top 25

cm of soil surfaceHigh runoff potential (HSG C and D)

• Surface water hydrology 39-yr record Discharge and Sediment Weather station and rainfall network

• Surface water quality 19-yr record Nutrients Herbicides

Goodwater Cr. Watershed



Day of Year150 155 160 165 170 175

Atra

zine

Con

cent

ratio

n (

g

L-1

)

0

10

20

30

40

50

60

Stre

am D

isch

arge

(L s

-1)

0

2000

4000

6000

8000

10000

Atrazine ConcentrationStream Discharge

Day of Year120 125 130 135 140 145 150

Atra

zine

Con

cent

ratio

n (

g

L-1

)

0

10

20

30

40

50

60

Stre

am D

isch

arge

(L s

-1)

0

2000

4000

6000

8000

10000

Day of Year120 125 130 135 140

Atra

zine

Con

cent

ratio

n (

g

L-1

)

0

10

20

30

40

50

60

Stre

am D

isch

arge

(L s

-1)

0

2000

4000

6000

8000

10000

1993

2001

2006

Atrazine ConcentrationsIn Goodwater Creek

• Persistent, high atrazine concentrations resulted in exceedance of EPA ecological criteria in 10 of 15 years (1992-2006)

• Pattern of high atrazine concentrations following spring runoff events suggested that interflow (flow over the saturated claypan) may be the cause

Surface Soil

Claypan

Interflow

Alluvial Aquifer

Alluvial Aquifer Recharge

StreamChannel

Surface Soil

Claypan

InterflowSeep

Surface Seep Recharge

SummitSide slopeToe slope



Goodwater Creek - Trends in Herbicide Loads

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

0

50

100

150

200

250

300

f(x) = − 3.26615357143 x + 66.8548952381R² = 0.264237317575991

Load

(kg)

y = -2.5x + 148r2 = 0.02

Atrazine MetolachlorMetolachlor Trend


Planting and Runoff Timing

Day of Year90 100 110 120 130 140 150 160 170 180 190 200 210 220

Cor

n Pl

antin

g Pr

ogre

ss (%

)

0

10

20

30

40

50

60

70

80

90

100

Stre

am D

isch

arge

(L s

-1)

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

Planting ProgressStream Discharge

1996

74

109

19

66

0.9

Critical Loss Period

Atrazine mass transported (kg)

Large runoff events during the critical loss period

Planting and Runoff Timing

Day of Year90 100 110 120 130 140 150 160 170 180 190 200 210 220

Cor

n Pl

antin

g Pr

ogre

ss (%

)

0

10

20

30

40

50

60

70

80

90

100

Stre

am D

isch

arge

(L s-1

)

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

Planting ProgressStream Discharge

2.0

1.0

0.6

1.2

Small runoff events at the end of the critical loss period

Critical Loss Period

Atrazine mass transported (kg)

2000



What Factors Control the Annual Variation in Atrazine Load?

Development of a Cumulative Vulnerability Index

)(

1

* ktLA

iii eEvDW

DWi = the daily weight; Evi = runoff event indicator, 0 if the daily discharge <10 mm/d and 1 if daily discharge was >10 mm/d; k = 0.0625/d; first-order rate constant for atrazine soil dissipation kinetics, Ghidey et al.(2005);t = time, in days; and LA = the length of time over which the daily weights were computed, chosen to be 100 days.

Daily Weight

LS

jjj DPDWCVI

1

*

Cumulative Vulnerability Index

CVI = cumulative vulnerability index;LS = the length of the planting season for a given year. DPj = the daily planting progress fraction; daily planting progress was used as a surrogate for herbicide application timing, and this data was obtained from weekly planting progress data for the northeastern crop reporting district (USDA-NASS, 1992-2006).



0.000 0.010 0.020 0.030 0.040 0.050

Ann

ual A

traz

ine

Load

(lbs

)

0

100

200

300

400

500

600

700

1992-2006 2007 and 2008Regression line,r2 = 0.63

2008

2007

The CVI accounts for:• Atrazine

application timing • Occurrence and

timing of runoff events

• Dissipation of atrazine in soils


Dry Year Wet Year



Generalized Cumulative Vulnerability Index

)(

11

*** ktLA

ii

LS

jj

WS

CSg eEvDP

ARACVI

Where:Acs = area planted to corn and sorghum;Aws = area of the watershed;R = atrazine application rate, assumed to be 1.63 kg/ha for this 4-year period;k = 0.06117 (Ghidey et al., 2010), first-order atrazine soil dissipation rate

Generalized Cumulative Vulnerability Index


Youngs Creek – June 2006 Runoff Event

Process-Based Index Model for Assessing Risk of Contaminant Transport

Flow-Chart of Process-Based Index Model

SSURGO –Soil and

Landscape Properties

by Soil Series (SS)

Soil and Hydrologic Weighting Functions

Herbicide and Soil Properties

Dissipation Functions

Sorption – Partition between

Solution and Sorbed Phases

Degradation – Applied to Solution

and Sorbed Compound

Landscape Risk

RiskSS = Remaining Herbicide(t)/Landscape

Risk

Three hydrologic transport pathways considered: leaching; solution runoff (SRO); and particle adsorbed runoff (ARO)

Watershed Scale Risk of Atrazine Transport in

Runoff Youngs Creek Watershed

Process-based index model that accounts for claypan hydrology Soil properties used to

assess risk (SSURGO) Includes spatial and

temporal risk Topsoil depth over

claypan and slope are key risk factors

Day 30

LowHighTransport Risk

Day 1Day 0.1

Day 7

6.02

4.29 2.92

6.84

Summary and Conclusions• Identified claypan and restrictive layer soils as being most

vulnerable to herbicide transport At the regional-scale, mass input of agricultural chemicals was

not the key factor controlling contamination of streams.

• Within a watershed, the CVI showed that annual variation in atrazine loads was a function of: Atrazine application progress (planting progress as surrogate) Occurrence/timing of runoff events Dissipation of atrazine in soils

• Process-based index model showed that slope and topsoil depth over the claypan were key landscape factors associated with atrazine transportTranslating Missouri USDA-ARS Research and Technology into Practice

A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO

Value of Monitoring Data• Provides needed information about the scope and

seasonality of contaminant transport, leading to the development of hypotheses and practical solutions– CVI explains annual variation in atrazine transport

Directly applicable to 3.3 Mha in the Central Claypan Areas and applicable to portions of another 15 Mha within the Corn Belt

– Process-based indices can predict risk of pesticide transport across the Corn Belt

• Monitoring informs policy– Identification of vulnerable areas for targeting conservation

practices (NRCS, SWCDs)– Effectiveness of conservation practices (NRCS, SWCDs)– Re-registration of atrazine by EPA

Possible label restrictions for restrictive layer soils


Documents

Robert N. Lerch