TRACE ELEMENT IN DIFFERENT MARINE TRACE ELEMENT IN DIFFERENT MARINE SEDIMENT FRACTIONS OF THE GULF OF SEDIMENT FRACTIONS OF THE GULF OF

TUNIS: CENTRAL MEDITERRANEAN SEATUNIS: CENTRAL MEDITERRANEAN SEA

NoureddineNoureddine Zaaboub1*, Zaaboub1*, WalidWalid Oueslati2, Oueslati2, SaadiSaadi Abdeljaoued2, F. Javier Abdeljaoued2, F. Javier Huertas3, Alberto LópezHuertas3, Alberto López--Galindo3Galindo3

1 1 NationalNational InstituteInstitute of of ScienceScience and Marine and Marine TechnologyTechnology, , SalambooSalamboo, , TunisTunis, , TunisiaTunisia

2 2 ScienceScience UniversityUniversity of of TunisiaTunisia, Manar, , Manar, Tunis,TunisiaTunis,Tunisia3 Instituto Andaluz de Ciencias de la Tierra. CSIC 3 Instituto Andaluz de Ciencias de la Tierra. CSIC –– UGR. UGR. 18002 Granada, 18002 Granada, SpainSpain*nouri_zaaboub@yahoo.fr*nouri_zaaboub@yahoo.fr

Introduction

Grain size distribution of surface sediment

Mineralogy of different sediment fractions

Contents

Geochemistry of surface sediment fine fraction

Statistical analysis:PCA and Cluster analysis

Conclusion

Bizerte

Mediterranean sea

N

Tabarka

Jendouba

Ghardimaou

Oued

Medje

rda

Oued Zerga

Oued Silia

na

Oued TessaOued Mellégue

Oued Rhezla

SousseKairouan

Tunis

Gulf of Tunis

1

2

3

9

1018

17

16

2223

24

26

25

3031

32

34

38

33

39

40

41

42

47

48

49

Kallat AlAndalous

N

8

15

46

Lagune de Ghar El Melh

Introduction

In the North of Tunisia the major wind period ismarked by strong and frequent North Westdirection.

Outle t o f Mejerda River

Outlet fo Ghar le Melh Lagoon

Topography of the gulf of Tunis

Fig1: Study area and sampling sites of

surface sediment in the north of Tunisia

Tunisia

Algeria

100 Km0

3

567

11

12

18

19

21

27

28

29

35

36

37

43

44

45

50

51

52

Oued Mejerda

Gammart 0 5 Km

4

13

14

20

Kaliji Chenal

direction.

This wind engenders littoral currents, gyratingcurrent anticlockwise forms in the centre of thegulf, forming weak current in the central part.

Sediment dynamics along a littoral zone isclosely dependent on the direction and theintensity of the littoral currents.

The Gulf of Tunis is connected to two principalwater flows, the Mejerda River and the Ghar elMelh lagoon.

Silt

100

80

60

40

20

0

0

100

80

60

40

20

Clayey silt

Sandy silt

Silty c lay Silty sand

Clayey sandSandy c lay

Grain size distribution of surface sediment

The clayey silt and the sandy silt represent themain fractions.

We are interested in the fraction which is <63µmthat is often selected for geochemical analysis.

Fig 2: Ternary diagram of particle size fractions of surface sediment

SandClay100

0 20 40 60 80 100

0

Three surface sediment fine fractions areseparated (<2µ, 2-20µ, 20-63µ) for Major andtrace element.

The particles that are less than 2 µm constitutethe clay fraction, a fine silt fraction (2–20 µm)and a mixture of fine and coarse silt fractions(20-63 µm).

µmµm < 2< 2 22--2020 2020--63 63 Max 25 80 80Min 5 30 2

Average 16 60 19

Table 1: particle size fractions of surface sediment less than 63µm

Fig3: Distribution of fine fractions of surface sediment

45678910111213141516171819202122232425

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

0- 2µ 2-20µ-5

0

5

1015

202530

3540

4550

55

60

6570

75

80

85

20-63µ

Gha r El MelhLagoon

Mejerda

Rive

r

CanalKhalij

36.9

37

37.1

10 .2 10.25 10.3

36.9

37

37.1

36.9

37

37.1

10.2 10 .25 10 .3 10.2 10.25 10.3

Gha r El MelhLagoon

Mejerda

Rive

rCanalKhalij

Gha r El MelhLagoon

Mejerda

Rive

r

CanalKhalij

Fig3: Distribution of fine fractions of surface sediment in the outlet of Mejerda River

In the central zone, the clay and the fine silt fraction are dominant 75-95%.

The fine and coarse silt fraction is dominant in the coastal zone. However, in thecentral zone there is a punctual accumulation by the presence of a region of offshoreoutcrops.

CoastalCoastal zonezonesmectitesmectite IlliteIllite KaoliniteKaolinite ChloriteChlorite II-- SS quartzquartz

< 2 µm< 2 µm 2828 2525 34 55 88 7722--20 µm20 µm 3030 2424 3434 66 66 1313

2020--63 µm63 µm 1818 3333 3232 66 1111 2929Central zoneCentral zone

smectitesmectite IlliteIllite KaoliniteKaolinite ChloriteChlorite II-- SS quartzquartz< 2 µm< 2 µm 2323 2525 4040 55 88 7722--20 µm20 µm 2424 2525 3939 66 66 1515

Table 2: average of clay minerals and quartz in surfacialsediment

Mineralogy of different sediment fractions

22--20 µm20 µm 2424 2525 3939 66 66 15152020--63 µm63 µm 1212 3434 3737 66 1111 3030

Dominant phases are dioctahedral smectite, illite and kaolinite. Chloriteand interstratified illite-smectite are also present.

Smectite percentage is higher in the coastal zone compared to the centralone.

Quartz percentage is almost the same in the coastal zone and the centralzone.

Smectite and fine Quartz grainsize are accumulated in littoralzone and in the central part ofthe Gulf.

The distribution of smectite 31

322829

23

24Gha r El MelhLagoon

0- 2µ 2-2 0µ 20-63µ

44.55

5.56

6.57

7.588.5

99.5

1010.5

11

11.512

12.513

13.5

Quartz7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

6

8

10

12

14

16

18

20

22

24

26

28

30

32

34Gha r El MelhLagoon

Mejerda

River

CanalKhalij

Gha r El MelhLago on

Mejerda

Rive

r

CanalKhalij

Gha r El MelhLago on

Mejerda

Rive

r

CanalKhali j

Gha r El MelhLagoon

Gha r El MelhLagoon

36.9

37

37.1

36.9

37

37.1

36.9

37

37.1

10.2 10.25 10.3 10.2 10.25 10.3

Quartz Quartz

Fig 4: Distribution of quartz and smectite in different

grain size fration of surfacial sediment

The distribution of smectiteand fine particles of Quartzfollow the principal coastaldrift directions.

10.2 10.25 10.315

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Smectite9101112131415161718192021222324252627

67

8

9

10

11

12

13

1415

16

17

18

19

20

21

2223Lagoon

Mejerda

Rive

r

CanalKhali j

36.9

37

37.1

36.9

37

37.1

36.9

37

37.1

10.2 10.25 10.3 10 .2 10.25 10.3

Smectite Smectite

Ghar El MelhLagoon

Mejerda

River

Ghar El MelhLagoon

Mejerda

River

Geochemistry of surface sediment fine fraction

Total organic carbon shows a lowaccumulation in front of Mejerda Riverand Ghar El Melah Lagoon.

Most part of total organic carbon isconcentrated in the south part of the gulf.

Fig 5: Distribution of TOC and C/N in the surfacial sediment

Canal Khalij

TOCC/N

Canal Khalij

concentrated in the south part of the gulf.

The C/N ratio shows a terrestrial organicmatter influence mainly in front of GharEl Melh lagoon (16), Mejerda River (12)and in the south part of the gulf (17).

Table 3: Average of major element in surfacial sediment

(%)Si

O2

Al2

O3

Fe2O

3

MnO

MgO

CaO

Na2

O

K2O

TiO

2

P2O

5

SO3

< 2µm 45.91 22.69 8.87 0.02 2.08 0.95 0.29 2.55 1.22 0.17 0.23

2-20µm 51.33 20.32 7.88 0.02 1.85 0.85 0.26 2.26 1.09 0.15 0.25

20-63µm 59.62 17.35 6.39 0.02 1.61 0.75 0.23 1.97 0.95 0.13 0.21

The coarse fraction (20-63µm) in comparison to fine fraction (<2µm) is richerin SiO2 signifying the presence of non-clay minerals such as quartz confirmedby X-ray diffraction.

The reverse trend is noticed in Al2O3 and Fe2O3. The weight percentage ofMnO remains constant in both fractions with an average of 0.02%.

Table 4: Average of trace element in surfacial sediment

ppmC

l V Cr

Co Ni

Cu

Zn

Ga

Br

Rb Sr Y Zr

Nb I Ba

Pb

< 2µm 429 223 218 5 72 62 209 31 47 120 196 14 300 28 45 271 25

2-20µm 380 197 192 4 64 55 184 27 42 106 173 12 266 25 40 239 22

20-63µm 333 172 167 4 56 48 160 24 36 93 151 11 230 22 35 208 19

The distribution of Pb is homogenous in the threefractions.

Ghar El MelhLagoon

fractions.

A little accumulation of Pb is observed in the fine fraction(<2µm) in the outlet of Mejerda River (65ppm).

The repartition of Cu, Zn and Zr represent a relativeaccumulation in the fine fraction (<2µm).

Spacial distribution shows an accumulation of Zn in frontof mejerda river.

Zn

Pb

Mejerda

River

Canal Khalij

Ghar El MelhLagoon

Mejer da

R iver

Canal Khalij

PCA statistical analysis, identified threecomponents that explained 67%, 94% and 64% ofthe total variance respectively in the threefractions <2µm, 2-20µm and 20-63µm.

There is a clear affinity between total iron and agroup of trace elements except Pb (Group I). Thiselement is in association with Smectite in 2-20and 20-63µm fractions in respectively Group IVand III.

0.5 1.0

0-2µm

MnO

MgO Fe2O3Zn

Y

P2O5

Kaolinite

Br QuartzSr

V

TiO2

K2O

Cr

CuNi

Al2O3

GaRb

Nb

0.0

0.5

1.0

-1.0

-0.5

Compenm

en t 2

-1.0 -0.5 0.0Compenment 1

SiO2Smectite

PbNa2O

Zr

Ba

Cl

ITOC

0.0

0.5

1.0

ompenm

e nt 2

2-20µm

SmectitePb

Na2SO4

ZrY

Ba Fe2O3MgOZn

P2O5

MnO

Cl

Cu NiK2O

Al2O3

CrSr

Br

I

TiO2

NbRb

V

GaKaoliniteTOC

I

II

III

IV

I

II

IV

Statistical analysis

Fig6:Loading of the variables on the first two principal components

and III.

The association phenomena took place in theMejerda river and Ghar el Melh lagoon.

Mlayah and al [2009] have shown that suspendedparticles in rivers scarvege trace elements byferrous, manganese and phosphorous hydroxides.

A second group of trace element is associated toalluminosilicates in the three fractions (GroupII).

0.0

0.5

1.0

-1.0

-0.5

Compenm

ent 2

-1.0 -0.5 0.0 0.5 1.0

Compenment 1

20-63µm

SiO2

Smectite

Pb

Na2O

Zr Y

Ba

Fe2O3

MgO

ZnP2O5

MnO

Cl

Cu Ni

K2O

Al2O3Cr

Sr

Br

I

TiO2

Nb Rb

VGa

Kaolinite

TOC

Quartz

-1.0

-0.5

Co

-1.0 -0.5 0.0 0.5 1.0

Compenment 1

SiO2

GaKaoliniteTOC

Quartz III

I

II

III

The cluster analysis allows us to classify thesediments in terms of their inter-metallic andcomposition ratios.

In the fraction < 2µm, Group 1 is characterized by arelatively highest average metal concentrations Fe,Pb, Zn, Ni and Cr. Most of the sites of this group arein front of Mejerda river.

In coarser grain size sediment (2-20µm), Group 118

19

17

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N

2-20µm

Group1

Group2

Group3

Group4

1

2

3

9

10

11

16

22

Kallat AlAndalous

42

43

44

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N

2µm

Group1

Group2

Group3

Group4

Group5

1

2

3

567

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47

Mejerda River

Ghar El MelhLag oon

Ka lla t AlAnda lous

Gammart 0 5 Km

Cana l Kalij

Gha r El MelhLa goon

Fig7: Classification of the sites based on the cluster analysis

In coarser grain size sediment (2-20µm), Group 1contains an extended area of potential sources ofmetals contaminants in the region, mainly Zn, Cuand Pb.

In grain size fraction between (20-63µm) there areGroup 2 and 5 which form two areas: the northernarea (lowest metal average) and the southern one(high metal average).

1

2

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Kalla t AlAndalous

Gammart

N

0 5 Km

19

21

27

28

29

35

36

37

44

45

50

51

52Gammart

20-63µm

Group4

Group5

Group1

Group2

Group3

Group4

Group5

567

12

5 Km0

Me je rda River

Canal Kalij

Mejerda Rive r

Ghar El MelhLagoon

Canal Ka lij

Conclusion

Trace element reflects mining in the gulf of Tunis.

In the different fractions <2µm, 2-20µm and 20-63µm traceselements are associated to hydrogenous fraction from watersource outlet.

There is a week degradation of TOC, mainly in front of Ghar elMelh lagoon and in the Southern part of the Gulf.

Trace element areal accumulations are clearly Distinguishaccording to their grain size fractions by cluster analysis incoastal sites in front of Ghar el Melh lagoon and in front ofMejerda River.