MOBILITY OF 137Cs, 10Be AND 210Pb IN SOIL AS

A FUNCTION OF THE SOIL TEXTURE,

ORGANIC MATTER CONTENT AND pH

F. DE TOMBEUR1, 2; S. CORNU2; D. BOURLÈS2; J. PUPIER2; I. LEFEVRE3; O. EVRARD3

Aix-Marseille Université,

CNRS, IRD, INRA,

13545 Aix en Provence,

France

(CEA-CNRS UVSQ), Université Paris-Saclay,

F-91198 Gif-sur-Yvette Cedex, France

INTRODUCTION Vertical matter transfer processes in soils and their dynamics are up to now poorly constrained although they are responsible for the temporal evolution of the ecosystem services of the soils through the redistribution of most of their components with depth, especially the finest ones responsible for the main properties of soil surface layers. In order to better constrain and quantify these processes, we developed a kinetic quantification of the involved transfers based on vertical profiles of 210Pb, 10Be, 137Cs and C isotopes in Luvisols. All these elements penetrate the soil system

Dedycas

CONCLUSION

This demonstrates that 10Be and 137Cs losses occur under soluble form in Podzol, especially those developed under more acidic forest cover. Soluble 10Be transfers are also evidenced in Andosol while they can be considered as negligible in Leptosol. For 210Pb (xs), soluble transfers are also probable for soils with pH less than 5.5 (Andosol and Ferralsol) and strong affinity for organic matter has been demonstrated. Thus, under acidic conditions and low < 2 µm fraction, soluble transfer cannot be neglected anymore. Reference: Campforts, B., et al., 2016. Earth and Planetary Science letters 439, 143-157.

< 2µm (g.kg-1)

pH

Podzol Leptosol Ferralsol Andosol Luvisol

Corn

OC (g.kg-1)

Forest

10Be (x108 atomes.cm-3)

137Cs (x10-3 Bq.cm-3)

210Pb (xs) (x10-3 Bq.cm-3) Scale for the litter

De

pth

(c

m)

Concentrations in 10Be as a function of the Kd<2µm (Campfort et al., 2016) obtained using the following equation:

KdClay=10a/(1+exp(-(b1+(b2*pH)))

with a=5.82 ; b1=-1.82 ; b2= 0.55.

While 10Be affinity for < 2 µm fraction is low in Podzol and Andosol, it is high in the Leptosol and intermediary in Luvisols. 0

5

10

15

20

25

30

35

0,00E+00 5,00E+04 1,00E+05 1,50E+05 2,00E+05 2,50E+05 3,00E+05

KdClay (Campfort et al., 2016 ; cm3.g-1)

Luvisols_MonsLuvisols_FeucherollesLuvisol_BoignevillesPodzol_ForêtPodzol_MaïsLeptosol_O3HPAndosol_Laqueuille

KdClay high affinity domain (Campfort et al., 2016)

Kd

Cla

y lo

w a

ffin

ity

do

mai

n

(Cam

pfo

rt e

t al

., 2

01

6)

Forest Corn

y = 3,063x - 128,08 R² = 0,9918

0

100

200

300

400

0 20 40 60 80 100 120 140 160OC (g.kg-1)

Leptosol_O3HP

y = 1,039x - 10,693 R² = 0,9908

y = 1,2325x - 77,837 R² = 0,966

y = 2,4995x - 28,887 R² = 0,957

0

20

40

60

80

100

0 20 40 60 80 100 120 140 160

Luvisol Feucherolles Forêt

Andosol

Ferralsol210Pb (xs) activities are a function of the organic carbon in most of the considered soils

y = 0,0084x + 0,9068 R² = 0,7802

y = 0,0117x + 0,8884 R² = 0,891

y = 0,0192x + 0,3907 R² = 0,8276

y = -0,0338x + 14,81 R² = 0,8561

0

5

10

15

20

25

30

35

0 100 200 300 400 500 600

10B

e (

*10

8a

tom

es

.gr-

1)

< 2µm (g.kg-1)

Luvisols Mons

Luvisols Feucherolles

Luvisol Boignevilles

Podzol Forêt

Leptosol

Andosol

10Be concentrations are correlated to the < 2µm fraction in Luvisols, are anti-correlated to that fraction in Andosol and unrelated to that fraction in Podzol and Leptosol.

Depth of the 137Cs peak is a function of the mean < 2 µm concentration

y = -14,54ln(x) + 90,72 R² = 0,9974

0

10

20

30

40

50

60

0 100 200 300 400 500 600

Mean content in <2µm fraction (g.kg-1)

21

0P

b (

xs

) (B

q.k

g-1

)

De

pth

of

th

e 1

37C

s p

eak

(cm

)

ISOTOPES DEPTH DISTRIBTION

IMPACT OF SOIL CHARACTERISTICS

De

pth

(c

m)

De

pth

(c

m)

De

pth

(c

m)

De

pth

(c

m)

De

pth

(c

m)

10B

e (

*10

8a

tom

es.g

r-1)

through its surface and are known to be poorly soluble under certain physicochemical conditions (low organic carbon (OC) content and neutral to basic pH, both conditions encountered in Luvisols) for which the elements are retained on the clay particles. Along the studied Luvisols, vertical profiles of these isotopes were fitted by a single advection - diffusion equation, demonstrating (i) that their soluble transfer could be neglected under the encountered pedological conditions, and (ii) the potentiality of the approach to trace vertical particle transfers in soils. The range of applicability of this type of approach was nevertheless not tested. In this work, we analyzed 210Pb, 10Be, 137Cs in soils exhibiting organic matter, pH and less than 2 µm fraction gradients (Podzol, and Andosol Ferralsol). Acidic soils and large organic matter contents were considered.

3 8

A

A/C

C

A

E

Bh

Bs

Bs/C

C

3 8

Ap

E

Bh

Bs

Bs/C

C

3 8

A

Bt1/Bt2

Bt3

C

Bt/C

0

50

100

150

200

3 5 7 9

A

C

B

3 8

A

B2

B1

3 8

0 100 200

A

A/C

C

A

E

Bh

Bs

Bs/C

C

0 50

Ap

E

Bh

Bs

Bs/C

C

0 50

A

Bt1/Bt2

Bt3

C

Bt/C

0

50

100

150

200

0 20 40

A

C

B

0 100 200

A

B2

B1

0 50

A

E

Bh

Bs

Bs/C

C

0 20 40

Ap

E

Bh

Bs

Bs/C

C

0 20 40

A

Bt1/Bt2

Bt3

C

Bt/C

0

50

100

150

200

0 200 400 600

A

C

B

0 500

A

B2

B1

0 500 0 500

A

A/C

C

-

-

-

-

-

-

-

-

-

-

-

-

A

E

Bh

Bs

Bs/C

C

0 5

Ap

E

Bh

Bs

Bs/C

C

0 5

A

Bt1/Bt2

Bt3

C

Bt/C

-10

40

90

140

190

0 2 4 6

A

C

B

0 5 10

A

A/C

C

0 10 20

0 5 10

A

E

Bh

Bs

Bs/C

C

0 5 10

Ap

E

Bh

Bs

Bs/C

C

A

Bt1/Bt2

Bt3

C

Bt/C

-10

40

90

140

190

0 5 10

A

C

B

0 10 20

A

B2

B1

0 5 10

A

A/C

C

0 100 200

Ap

E

Bh

Bs

Bs/C

C

0 20

A

C

B

0 20 40 60

A

B2

B1

0 50 100 150

A

A/C

C

0 50 100 150

A

Bt1/Bt2

Bt3

C

Bt/C

-10

40

90

140

190

0 10 20

A

E

Bh

Bs

Bs/C

C

0 100 200

0 20

Scale for the soil

-

-

-

-

-

-

-

-

-

-

-

-

1: Biosystem Engineering Department, Gembloux Agro-Bio Tech, Université de Liége, Passage des Deportés 2, 5030, Gembloux, Belgique 2: Aix-Marseille Université, CEREGE, UMR CNRS 7330, BP80, 13545 Aix-en-Provence, Cedex 4, France 3: Laboratoire des Sciences du Climat et de l’Environnement (LSCE/IPSL), UMR8212 (CEA-CNRS-UVSQ), Domaine du CNRS, F-91198 Gif-sur-Yvette Cedex, France