http:// a spatially-distributed model of pesticide leaching aaldrik tiktak

http://www.pearl.alterra.nl

A spatially-distributed model ofpesticide leaching

Aaldrik Tiktak



Outline of presentation

• Why spatially distributed modelling?• What is GeoPEARL?• How is a GeoPEARL assessment carried

out?• Which are the main model outputs?• Selected Results and Examples• Questions?• Overview of the User Interface


Why spatially distributed modelling in registration?

Explicit consideration of the variability of the leaching process:

• where are the vulnerable regions?• Are specific areas (e.g. drinking water

abstraction areas) sufficiently protected?

Leaching in the area of use

Leaching in drinking water abstraction areas


Why spatially distributed modelling in registration?

Explicit calculation of ‘realistic worst-case conditions’:

• calculation of percentiles of the leaching concentration in space

• more realistic choice of standard scenario’s, no need for safety factors in registration

Position ofthe DutchStandardScenario


What is GeoPEARL?

•GeoPEARL is a spatially-distributed model of pesticide leaching to the groundwater and surface waters in the Netherlands. The core of the GeoPEARL consists of PEARL itself.


The PEARL model - a 1D-column

preci pitat ion

irrigati on

t ranspirati onevaporat ion of

intercepted water

soilevaporat ion throughfall

f luctuati nggroundwater

level

soil waterf luxes

ponding

water uptakeby plant roots

seepage

lateral

discharge toditches and

f ield-drai ns

un

sa

tura

ted

zo

ne

sa

tura

ted

zo

ne

depositi on

applicat ion

dissipation at thecrop canopy

volati lisation

wash-of f

convect iondispersiondif fusion

pestic ideuptake

leaching

t ransform ation

solid-liquidgas

partit ioning

SWAPhydrology

PEARLpesticide fate

cropcalendar

heatf low

inject ion

surface

run-off


Position of column in landscape

field-ditches

water courses< 3m

water courses> 3 m

PEARL 1Dcolumn

Leaching into theregional

groundwater

Groundwater table

Drainage into localsurface waters


Why a complex model??????


The plot appraoch

•PEARL is run in a GIS context for a large number of unique combinations (plots) of soil, climate, land-use and hydrogeological units.


Derivation of the unique combinations:


• Lower boundary of SWAP is upper boundary of National Groundwater Model;

• Start with NAGROM and a simple unsaturated zone model;

• Adjust the boundary flux by running NAGROM and SWAP iteratively;

• Wait until convergence is reached.

Obtaining the lower boundary of SWAP:

• Lower boundary condition is a prescribed flux condition (so-called ‘Neumann condition’);


Plots are represented by a single vertical column:

A plot


Basic soil properties in GeoPEARL

Slightly acidicsandy soils (‘higher part’)

Clay soils with near neutral pH-values (‘lower part’)

Acidic peat soils

pH-KCl!!!!!


How are GeoPEARL assessments carried out?

• GeoPEARL is run for 250-6405 plots, depending on spatial detail wanted;

• The model is run for the area of potential usage only. This area is assumed equivalent to the area of the crop(s) for which a registration is requested;

• For each plot and crop-type, the model is run for 26, 46 or 66 years (FOCUS procedure);

• For each plot the median leaching concentration in time is extracted and put into a map.


To be specified by the user:

•Substance properties (start withstandard dossier)

•Application schedule

•Number of plots (i.e. spatial detail wanted)

•One or more crops for which a registration is requested


More attention for relationship between soil properties and substance properties:• DT50 in top-soil specified as a function of clay

content, pH and organic matter content

• KF specified as a function of organic matter and pH:

eqsoxsoxeqclayclayeqsiltsilteqsandsandeqomomeqFeqF KcKmKmKmKmKK ,,,,,0,,,

H-Ka-pH

ac

H-Ka-H

ac,,aceq,.

101

10

ppba

pppbabaeqomom

omF,eq

MM

MM

KKmK

max,50,50max,50,50

H,.,50

,50

max,50,50min,50

min,50,50min,50,50

)HH()()(if

DTDTDTDT

ppfmmfmmfDT

DTDTDTDT

DTDTDTDT

plotplot

rprlllromomomr

plot

plot

plotplot

or as a function of other properties:


More attention for relationship between soil properties and substance properties:


The target variable produced by the model:

•The 90th percentile in space and the 50th percentile in time of the leaching concentration at 1 m depth at the area of (potential) usage


Further model outputs:

•Maps and frequency diagrams of terms of the water balances

•Maps and frequency diagrams of terms of the substance balances, including the leaching, drainage and volatilisation fluxes

•Maps of percentiles and frequency diagrams of the leaching concentration in time

•Tables of balance terms


Example 1: Comparison of leaching of two substances

High pH

Vulnerable sandy soils

Ordinary substance pH-dependent sorption

Opposite spatial patterns!


Example 2: Comparison of drainage and leaching

Drainage fluxes are highest in clay and peat soils...

Leaching fluxes are highest in sandy soils...


Some conclusions from previous examples:

• Drainage fluxes are generally higher than leaching fluxes.

• For ordinary substances, drainage dominates in the peat and clay soils and leaching in sandy soils.

• The leaching pattern can be quite different for non-ordinary substances (e.g. substances with pH-dependent sorption)


GeoPEARL considers the area of potential usage:

• Pesticides are usually authorised for particular crops;

• The new decision tree therefore considers the area of potential usage, approximated by the area of crops for which a registration is requested

• GeoPEARL is distributed with a database of areas for 24 major crops

• All results are presented for the area of potential usage


GeoPEARL crops are not hydrologically different

• During the derivation of the UC’s, only four crops were included (grass, mais, potatoes and forest);

• For each plot, the dominant crop is used. Hydrological parameters are assigned to these crops;

• The 24 GeoPEARL crops are used for pre-processing only; i.e. for calculating the area of use.


Effect of area of use on pesticide authorisation (1)

Maize is grown on slightly acidic sandy soils

Potatoes are grownon light sandy claysoils and in ‘the Veenkolonien’


Effect of area of use on pesticide authorisation (2)

Substance with pH-dependent sorption behaviour

Light sandy claysoils and ‘the Veenkolonien’

Slightly acidic sandy soils


Effect of area of usage on authorisation (cntd.)

Unsafe in potatoes

Safe in maize


Some conclusions from previous section:

• GeoPEARL explicitly considers the variation of the leaching process, so that it is now possible to evaluate the leaching for different crop types

• Consideration of the area of usage can have a strong effect on the authorisation decision

• It is extremely important to investigate the relationship between pesticide properties and soil properties


GeoPEARL assessments versus assessment items

• A notifier may wish to register for several crops;

• For each crop, GeoPEARL must be run separately;

• Combination of crop and application scheme is an assessment item;

• The three items together form an assessment;

• The 90th percentile is calculated for the combination of the three crops, i.e. for the assessment.


The GeoPEARL database

Project

Assessment

SubstanceAssessment

item

Model control(number of plotsto be includedin assessment)

Crop forwhich a

registrationis asked

AnnualApplication

scheme

Parents andmetabolites

Applicationevent

Repeatinterval

of application

Generalsubstanceproperties

Sorptionparameters

Transformationparameters

Crop relatedparameters

Diffusion relatedparameters

1:n

1:n1:11:1

1:1 1:1 1:1

1:n

1:n

1:11:1

1:11:11:1


Reduction of computation time by using zones:

• To reduce the computation time, plots are taken together;

• Clusters of plots are called ‘zones’.

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

1 1 1 1

2 2 2

2 3 3

3 4 4 4 4

5 5 5

Plots Zones

Plot without relevant crop

Plot with relevant crop

SLICE


Slicing is done on the basis of ‘vulnerability’

• The normal Arc/Info slice operation clusters neighbouring cells;

• We cluster plots with adjacent vulnerability indexes;

• This will give a more reliable estimation of the 90th percentile, because we sample in each class of the cumulative frequency distribution.


The vulnerability index for ordinary substances:


How many plots must be included in an assessment?

almost nodifference

these two aredifferent!


More plots = more detail, but 250 plots is generally enough...

How many plots must be included in an assessment? (cntnd.)


250 plots is generally enough...

250 versus 6405 plots

0.00001

0.0001

0.001

0.01

0.1

1

10

0.00001 0.0001 0.001 0.01 0.1 1 10

GeoPEARL_6405 (ug/L)

Geo

PE

AR

L_2

50

(ug

/L)

0.00001

0.0001

0.001

0.01

0.1

1

10

0.00001 0.0001 0.001 0.01 0.1 1 10

GeoPEARL_6405 (ug/L)

Geo

PE

AR

L_2

50

(ug

/L)

spring

autumn


Some conclusions from previous section:

• The maximum number of zones is 6405 (which is equal to the number of plots);

• A first impression of the leaching pattern can be obtained with less plots (e.g. the 30 as used in this course);

• At least 250 plots are required for an accurate estimation of the 90th percentile. This is the minimum number for a final submission.


Other uses of GeoPEARL

•GeoPEARL has been combined with a database on pesticide usage in order to calculate the actual pesticide loads into surface waters and groundwaters.

• Evaluation of policy plans...

•A European version of GeoPEARL (called EuroPEARL) has been developed

• EU registration in zones...


EuroPEARL example: 80th percentile of the leaching concentration of FOCUS substance D

Hotspots occur everywhere in Europe

High leaching risk


Possible scales…

Catchment

EU


• A model is now available that can be used to assess the leaching into the groundwater and the drainage into surface waters at a regional-scale

• The model is operational for:• the Dutch registration procedure• evaluation of policy plans

Final remarks


The Graphical User Interface

GeoPEARLUser

Interface

GeoPEARLUser

Interface

GeoPEARLexecutable

GeoPEARLexecutable

XYWinviewer

XYWinviewer

GeoPearldatabase

GeoPearldatabase

ReportReport

MapsMaps

PEARLmodel

PEARLmodel


First install the program….

Download geopearl_1_1_1.exefrom the address

http://www.pearl.alterra.nl.

Archive this application

Logon with administrator rights

Run geopearl_1_1_1.exe to install GeoPEARL

Launch GeoPEARL to install Interbase

Logon with your own user name

Start using GeoPEARL; register at the PEARL website

If FOCUS PEARL 2.2.2 is installed:launch FOCUS PEARL as well


To be specified by the user:

•Substance properties (start withstandard dossier)

•Application schedule

•Number of plots (i.e. spatial detail wanted)

•One or more crops for which a registration is requested


Getting started with the User Interface

Add or edit a substance .Parameters must be given for parent substances and for metabol ites

Add or edit a substance .Parameters must be given for parent substances and for metabol ites

Add or edit app lication schemes.Each assessment item may have i ts own application scheme.

Add or edit app lication schemes.Each assessment item may have i ts own application scheme.

Use the wizard to generate assessments.An assessment consists o f a single substance and one or assessment items.

Use the wizard to generate assessments.An assessment consists o f a single substance and one or assessment items.

Review the input and correct where necessaryReview the input and correct where necessary

Select assessments for execution andpush the ca lcu late button to start the simulations

Select assessments for execution andpush the ca lcu late button to start the simulations

View reports, graphs and mapsView reports, graphs and maps


GUI step 1: Main form


GUI step 2: Edit substance properties


GUI step 3: Edit application schedules


GUI step 4: Run wizard, select substance and resolution


GUI step 5: Run wizard, select crops and applications (i.e. add items)


GUI step 6: Run GeoPEARL


The model is running….


GUI step 7: Select output - Assessment as a whole


GUI step 7: View output - Assessment as a whole


GUI step 8: Select output - Assessment item


GUI step 8: View output - Assessment item


GUI step 9: View report (assessment as a whole)


GUI step 10: Analyse the output

http:// a spatially-distributed model of pesticide leaching aaldrik tiktak

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