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.
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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)
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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)
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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).
Cumulative Vulnerability Index
Cumulative Vulnerability Index
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
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
Dry Year Wet Year
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO
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
Translating Missouri USDA-ARS Research and Technology into Practice A training session provided by USDA-ARS-CSWQRU, 10-11 October 2012, Columbia, MO