Séverine Le Dizès Environment and Emergency Operations Division Department for the Study of Radionuclide Behavior in Ecosystems Environmental Modelling

Séverine Le Dizès

Environment and Emergency Operations Division Department for the Study of Radionuclide Behavior in Ecosystems Environmental Modelling Laboratory

Cadarache, St Paul-lez-Durance, France

September 28th, 2009

TOCATTA : Transfer Of Carbon 14 And

Tritium in Terrestrial and Aquatic environments

EMRAS II, Paris, 09/28/2009

Plan

vPresentation of VATO

vConclusions & perspectives

vPresentation of TOCATTAØConceptual model

ØMathematical model


C and H specificities

Presentation of TOCATTA

1. Integration of these radionuclides to living organic matter

2. Carbon14 and Tritium transfers within biotic compartments occur in the form of :§ Organic matter and carbon dioxide (for 14C)§ Organic matter and tritiated water (for tritium)

Ø More specifically, dynamic modeling of 14C and 3H in plants requires knowledge of plant growth dynamics

Ø 14C and 3H modeling (stocks, fluxes, residence time) does require dynamic models of biomass evolution (plant, animal and/or microbial)

All these chemical forms are directly related to biomass (spatial and temporal growth), unlike other radionuclides


Current 14C and 3H modeling in TOCATTA


§ Multiple source term kinetics : normal / accidental modes

§ Main environmental media : agricultural systems (soil, plant & animals)

§ Atmospheric and/or liquid releases

§ Temporal scales :ü Daily time stepü During one or several years

§ Dose man calculations through ingestion of contaminated foodstuffs (SYMBIOSE)


Diffusion 14CO2

HTOvapor

PrecipitationSource

HTO

14CO2

NetPrimaryProduction

Foliar absorption

Evapotranspiration

irrigation

Root absorptio

n

14C pathways 3H pathways 14C and 3H pathways

infiltration

Microbial activity

HTO

14Corganic

Évaporation HTO

OBT

translocation

Literfall

HTO

Biological decay


Conceptual model Presentation of TOCATTA

Plant

(Organ)

OrganicMatterRadioactiveDecayBiologicalGrowth

Grazing*

RestOfPlant

NetPrimaryProductionDiffusion

RestOfWorld

Ø Carbon 14

Plant

(Organ)

WaterRadioactiveDecay

BiologicalDecay

Grazing*

OrganicMatterRadioactiveDecayBiologicalGrowth

Grazing *

RestOfPlant

FoliarAbsorptionWetInputPlantTranslocationRootUptakeTranslocation

NetPrimaryProduction

RestOfWorld

Ø Tritium

*For grass only

Winter cerealsSpring cereals

Fruit vegetable

Root vegetables

Leaf vegetables

Grass

Winter cerealsSpring cereals

Fruit vegetable

Root vegetables

Leaf vegetables

Grass

Mathematical model (1)



§ First order differential equations

)14141414(1

]14_[ ._

.RadP

GraP

DiffSP

NppP

OmPSP TCTCTCTCCC

dt

d

§ Mass conservation balance of pollutant in each compartment

§ Example : Transfer of 14CO2 from Air to Grass :

NetPrimaryProductionDiffusion GrazingRadioactiveDecay

Plant dry density

Logistic or exponential model

Mathematical model (2)



Air

AirP

Gro

OmPNppP CC

CCCC

dt

dTC

]12_[

]14_[]12_[14 _

Air

_

][

]3_[][

H

DIFDHCpH

dt

dTOBT P

fPAirHTO

P

Gro

OmPNppP

Assumptions :

1. Use of a daily time step (current version)

2. Isotopic equilibrium between newly created plant biomass and surrounding air, at each time step

3. Growth curves are logistics (cereals) or exponential (grass, leaf-, fruit- or root vegetables)

4. Isotopic discrimination factor for tritium entering plant organic matter


VATO

VAlidation of TOcatta

Presentation of VATO

Séverine Le Dizès1, Denis Maro2 & Didier Hébert2

1IRSN/DEI/Environmental Modelling Laboratory/Cadarache, St-Paul-lez-Durance

2IRSN/Laboratory of Continental Radioecology/Cherbourg-Octeville


Goals

v Estimate fluxes of 14C and 3H in a grassland ecosystem (Raygrass), in relation with : - 14C and 3H concentrations in air,- Climate conditions,- Land use (grazing, maïze silage and hay).

v Study transferts of 14C and 3H to cows and cowmilk in function of the alimentary diet.

In order to validate the TOCATTA model



Agenda Carbon 14

2007-2009 : Transfers between air, grass and soil

Tritium

2010 : Measurement (speciation of 3H releases in air)

2009-2010 : Transfers to cow

2008-2009 : Model-measures comparisons

2010 : Publication

2010-2011 : Transfers between air, rain water, grass and soil2012 : Transfers to cow

2012 : Publication

2011-2012 : Model-measures comparison


Wind conditions 2008 - "Omonville La Petite". Wind speed (m.s-1) and Direction (°)

0

2

4

6

8

10360

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

320

340

fréq dir (%)

Site location


« Atelier Nord » : a well located experimental site, considering the most frequent wind directions

Important concentrations in the environment


Important releases of 14C and 3H by the AREVA NC La Hague reprocessing plant

Experimental design


Continuously Recording Field Monitor for Krypton-85

10 m mast with sonic anemometer (turbulence)

Weather station

LabMeteorological data acquisition

CO2 measurement acquisition (LICOR 7000)

Fram

Grass (Raygrass)

14C trapping device (bubbe gas through soda)



1. Use of a daily time step

3. Air concentration data are measured each monthØ Daily air concentration inputs are assumed to be constant over the month

2. Grass growth is linear based on monthly dry weight dataØ Estimation of a daily growth rate

Main assumptions of the plant submodel

EMRAS II, Paris 09/28/2009

Comparison of measured and calculated 14C specific activities

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

01/08/06 09/11/06 17/02/07 28/05/07 05/09/07 14/12/07 23/03/08 01/07/08

Bq

/kg

C

Air

Measured Grass Zones1&2

Measured Soil Zones1&2

Uncontaminated Soil

Uncontaminated Grass

Simulated Grass Zones1&2


Measured Grass 14C activities > Measured Air 14C activities

> Simulated Grass 14C activities


Two ways of improving the comparison between modeled/measured activities :

1. Regarding the model itself : the specific activity concept is adapted for chronic releases

Need to improve the model in terms of kinetics to adapt it to time varying releases and meteorology

Use of an hourly-based growth model for grass in function of local meteorological data

2. Regarding the 14C releases : the atmospheric 14C concentrations are measured on a monthly basis

Need to improve the calculations in terms of kinetics (e.g. every hour)


Use of the hourly 85Kr data



A model of grass growth

Johnson et al. (1983) A model of Grass Growth, Ann. Bot. 51, 599-609.Johnson and Thornley (1983) Vegetative crop growth model incorporating leaf area expansion and senescence, and applied to grass, Plant, Cell and Environment 6, 721-729.

§ A compartmental model based on an hourly time step

Storage dry weight, WS

Light interceptionPhotosynthesis

Root growth and maintenance

Structural dry weight, WG

Growth respiration, Rg

Maintenance respiration, Rm

Senescence

Growth, G

SGdt

dWG

RmYGPdt

dWS

/

SGdt

dL

)/1( WsWm



Calculation of atmospheric 14C on an hourly basis

Krypton 85 : a good indicator of 14C atmospheric dispersion over a short periodicity

05000

1000015000200002500030000350004000045000500005500060000650007000075000

Heure T.U.

ac

tiv

ité

en

Bq

/m3

Samedi 30 Septembre 2006 LB111 (Atelier Nord)

Moy. mobile sur 10 pér. (Samedi 30 Septembre 2006 LB111 (Atelier Nord) )

param étres d'é talonnage:bdf: 26 cpscoefficient: 612 (4 com pteurs)

Hourly 14C atmospheric concentration


Comparison of measured and calculated aboveground dry matter



Comparison of measured and calculated 14C specific activities



ConclusionsPresentation of VATO

§ To adapt the model to time varying releases and meteorology, an hourly time-step is required :

§ The VATO projects supports the approach to use plant physiological parameters within 14C (and tritium) models

Ø To estimate 14C air concentration inputs to the model, based on hourly 85Kr data

Ø To simulate photosynthesis and plant growth dynamics


PerspectivesPresentation of VATO

§ To adress dynamic modeling of 14C and 3H in plants, ongoing effort should be addressed to improve the modelling of photosynthesis and dry matter production

§ Concerning 3H modelling in case of time varying releases and meteorology, it is also necessary to consider most of the relevant water transfer processes with a dynamic approach based on a short time step.

§ Use of PASIM*, a biogeochemical grassland ecosystem model that simulates fluxes of C, N, water and energy at the soil-plant atmosphere interface.

*Riédo et a., 1998. A Pasture Simulation Model for dry matter production, and fluxed of carbon, nitrogen, water and energy. Ecol. Model. 105, 141-183.

A collaboration starts in October with INRA (Clermont-Ferrand).


Compartment models (1)

Advantages

ü Simple structure (e.g. Model of Johnson, 2 compartments)

ü Generic, flexible : can be used to test scenarios

ü Simple ordinary differential equations

ü A simplification of the mathematical model (variables are represented as singli scalars instead of spatially distributed fields)


Compartment models (2)

Drawbacks

ü Can not be spatially explicit (e.g.PaSim : no spatial heterogeneity)ü The model parameters are less likely to be physiological (constant coefficients)

Thank you for your attention !

Documents

Séverine Le Dizès Environment and Emergency Operations Division Department for the Study of Radionuclide Behavior in Ecosystems Environmental Modelling