TRACE ELEMENT IN DIFFERENT MARINE SEDIMENT FRACTIONS OF THE GULF OF TUNIS: CENTRAL MEDITERRANEAN SEA

Noureddine Zaaboub1*, WalidOueslati2, SaadiAbdeljaoued2, F. Javier Huertas3, Alberto LópezLópez--Galindo3Galindo3 1 NationalInstitute of Science and Marine Technology,Technology , SalambooSalamboo,, Tunis,Tunis , Tunisia 2 Science University of Tunisia,Tunisia , Manar, Tunis,Tunisia 3 Instituto Andaluz de Ciencias de la Tierra. CSIC ––UGR.UGR. 18002 Granada, Spain *[email protected] Contents

Introduction

Grain size distribution of surface sediment

Mineralogy of different sediment fractions

Geochemistry of surface sediment fine fraction

Statistical analysis:PCA and Cluster analysis

Conclusion Introduction

Outlet fo Ghar le Melh Lagoon

Outle t o f Mejerda River

Mediterranean sea

Bizerte N

Tabarka Gulf of Tunis Topography of the gulf of Tunis 46 38 N Lagune de Ghar ezla Oued Zerga 39 47 Oued Rh Tunis El Melh 30 31 Ghardimaou 22 40 a n a li a i 23 48 rd Jendouba S je 32 ed d M e ed u u O 41 In the North of Tunisia the major wind period is O 15 24 Kallat Al 33 Oued Tessa Andalous 16 Oued Mellégue 8 25 1 9 17 42 49 marked by strong and frequent North West Sousse 34 Kairouan 2 10 26 18 3 11 35 43 4 19 27 50 direction . Oued Mejerda 5 12 6 13 20 Tunisia 28 36 7 14 Algeria Kaliji Chenal 21 44 51 This wind engenders littoral currents, gyrating 29 37 45 0 5 Km 52 Gammart current anticlockwise forms in the centre of the 0 100 Km gulf, forming weak current in the central part. Sediment dynamics along a littoral zone is Fig1: Study area and sampling sites of closely dependent on the direction and the surface sediment in the north of Tunisia intensity of the littoral currents. The Gulf of Tunis is connected to two principal water flows, the Mejerda River and the Ghar el Melh lagoon. Grain size distribution of surface sediment

Silt 0 100

The clayey silt and the sandy silt represent the 20 80 main fractions. 40 60 Clayey silt Sandy silt 60 40 We are interested in the fraction which is <63µm Silty c lay Silty sand that is often selected for geochemical analysis. 80 20

Sandy clay Clayey sand 100 0 Clay 0 20 40 60 80 100 Sand Three surface sediment fine fractions are separated (<2µ, 2-20µ, 20-63µ) for Major and Fig 2: Ternary diagram of particle trace element. size fractions of surface sediment

Table 1: particle size fractions of The particles that are less than 2 µm constitute surface sediment less than 63µm the clay fraction, a fine silt fraction (2–20 µm) and a mixture of fine and coarse silt fractions µmµm < 2< 2 22--2020 2020--6363 (20-63 µm). Max 25 80 80 Min 5 30 2 Average 16 60 19 25 Ghar El Melh Ghar El Melh 80 Ghar El Melh 85 24 Lago on Lago on Lago on 80 23 75 75 22 70 21 70 65 37.1 20 37.1 37.1 65 19 60 60

18

a 55 55

a

a

17 d

r

d

d

r

r

r

r 50

r

e 50

j

e

e

16 e

j j

e

e

e

v

v e e

v

i 45 i

i 15 45

M

R

R

R M 14 M 40 40 13 35 37 37 12 35 37 30 Ca nal 11 Ca nal 30 Canal 25 Khalij 10 Khalij Khalij 25 20 9 8 20 15 10 7 15 6 5 10 5 2-20µ 0 36.9 0- 2µ 36.9 36.9 20-63µ 4 5 -5 10.2 10 .25 10 .3 10.2 10.25 10.3 10 .2 10.25 10.3

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 the central zone there is a punctual accumulation by the presence of a region of offshore outcrops. Mineralogy of different sediment fractions

Table 2: average of clay minerals and quartz in surfacial sediment Coastal zone smectite Illite Kaolinite Chlorite II--SSquartz < 2 µm 2828 2525 34 55 88 77 22--2020 µm 3030 2424 3434 66 66 1313 2020--6363 µm 1818 3333 3232 66 1111 2929 Central zone smectite Illite Kaolinite Chlorite II--SSquartz < 2 µm 2323 2525 4040 55 88 77 22--20 µm 2424 2525 3939 66 66 1515 2020--6363 µm 1212 3434 3737 66 1111 3030

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

Smectite percentage is higher in the coastal zone compared to the central one.

Quartz percentage is almost the same in the coastal zone and the central zone. 0- 2µ 2-20µ 20-63µ

13.5 Ghar El Melh Ghar El Melh 21 Ghar El Melh 34 Lago on 13 Lago on Lago on 20 Smectite and fine Quartz grain 12.5 32 12 19 30 11.5 37.1 37.1 18 37.1 28 11 17

size are accumulated in littoral 10.5 26

a a

10 16 a 24

d

d

r

r

d

r

r

r

e

r

e j

j 9.5

e

e

e j

15 e 22

e

v e

v

i

e i

9 v

i

M

zone and in the central part of R

R

M M 14 R 20 8.5 8 13 18 37 7.5 37 37 the Gulf. 12 16 Ca nal Ca nal Ca nal 7 Khalij Khalij 6.5 11 Khalij 14 6 10 12 5.5 9 10 5 Quartz 4.5 Quartz 8 Quartz 8 36.9 4 36.9 7 36.9 6 10.2 10.25 10.3 10.2 10.25 10.3 Ghar El Melh Ghar El Melh 32 29 Ghar El Melh 24 Lago on Lago on 31 28 Lago on 23 27 30 22 The distribution of smectite 26 21 29 25 37.1 37.1 37.1 20 28 24 19 27 23 and fine particles of Quartz 18

22 26 a

d 17 21 r

25 r

e j

20 e 16

e v

24 i R follow the principal coastal 19 M 15 23 18 14 22 37 37 17 37 13 21 16 drift directions. Ca nal 12 15 20 Khalij 11 14 19 10 13 18 9 12 17 11 8 16 7 Smectite 36.9 Smectite 10 Smectite 36.9 15 9 36.9 6 10.2 10.25 10.3 10.2 10.25 10.3 10 .2 10.25 10.3

Fig 4: Distribution of quartz and smectite in different grain size fration of surfacial sediment Geochemistry of surface sediment fine fraction

Total organic carbon shows a low Ghar El Melh Ghar El Melh accumulation in front of Mejerda River Lagoon Lagoon

and Ghar El Melah Lagoon.

a

a d

r

d

er

r e

Most part of total organic carbon is r

e

ej

j v

e i

e

v

R

M

i R concentrated in the south part of the gulf . M

Canal Khalij Canal The C/N ratio shows a terrestrial organic Khalij matter influence mainly in front of Ghar C/N El Melh lagoon (16 ), Mejerda River (12 ) TOC and in the south part of the gulf (17 ).

Fig 5: Distribution of TOC and C/N in the surfacial sediment Table 3: Average of major element in surfacial sediment SO3 CaO K2O SiO2 TiO2 MnO MgO P2O5 Na2O (%) Al2O3 Fe2O3 < 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 richer in SiO2 signifying the presence of non-clay minerals such as quartz confirmed by X-ray diffraction.

The reverse trend is noticed in Al2O3 and Fe2O3. The weight percentage of MnO remains constant in both fractions with an average of 0.02%. Table 4: Average of trace element in surfacial sediment I V Y Sr Zr Cl Cr Br Ni Pb Zn Ba Ga Co Cu Rb Nb ppm < 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

Ghar El Melh The distribution of Pb is homogenous in the three Lagoon fractions .

a

d

r

r

e

j

e

e

v

i A little accumulation of Pb is observed in the fine fraction M R Canal (<2µm) in the outlet of Mejerda River (65ppm). Khalij Zn The repartition of Cu, Zn and Zr represent a relative

Ghar El Melh accumulation in the fine fraction (<2µm). Lagoon

Spacial distribution shows an accumulation of Zn in front a

d

r

r

e

j

e

e

v

i of mejerda river. M R

Canal Khalij

Pb 1.0 0-2µm Zr Ba MnO Y Statistical analysis 0.5 Na2O MgO Fe2O3 I Pb Zn Cu P2O5 Smectite SiO2 Cl Ni

2

IV K2O

t

n PCA statistical analysis, identified three e 0.0 Cr

m

n Al2O3

e p Quartz components that explained 67%, 94% and 64% of m Br TiO2 o I Sr C TOC V II -0.5 Nb the total variance respectively in the three Rb Kaolinite III Ga fractions <2µm, 2-20µm and 20-63µm. -1.0 -1.0 -0.5 0.0 0.5 1.0 Compenment 1

1.0 MgO 2-20µm There is a clear affinity between total iron and a Ba Fe2O3 Zn Zr I K2O Y P2O5 Cu Ni Al2O3 group of trace elements except Pb (Group I). This 0.5 MnO II Na2SO4 Cr Cl Sr Br element is in association with Smectite in 2-20

2 TiO2

t Pb n I e Smectite 0.0 m Nb n V and 20-63µm fractions in respectively Group IV

e

p Rb

m IV Ga o TOC Kaolinite C SiO2 and III . -0.5 Quartz III

-1.0 The association phenomena took place in the -1.0 -0.5 0.0 0.5 1.0 Compenment 1 Mejerda river and Ghar el Melh lagoon. 1.0 20-63µm Ba I Br

0.5 Zr Fe2O3 I K2O Y MnO Mlayah and al [2009] have shown that suspended Sr II Na2O Zn P2O5 Quartz Kaolinite TiO2

2

t MgO Ni n Cu particles in rivers scarvege trace elements by

e Nb 0.0 Cr Rb

m

n SiO2 TOC Al2O3

e V

p Pb Ga ferrous, manganese and phosphorous hydroxides.

m o Smectite C Cl -0.5 III A second group of trace element is associated to

-1.0 -1.0 -0.5 0.0 0.5 1.0 alluminosilicates in the three fractions (GroupII). Compenment 1 Fig6:Loading of the variables on the first two principal components 38 2µm Ghar El Melh 39 47 Lag oon 30 31 22 40 N 48 23 32 41 Group1 24 Kallat Al 16 33 Anda lous 25 Group2 The cluster analysis allows us to classify the 1 9 17 42 49 34 2 10 26 18 sediments in terms of their inter-metallic and 3 Group3 11 35 43 19 27 50 Mejerda River 5 12 6 Group4 composition ratios. 28 36 7 21 44 Cana l Kalij 51 Group5 37 29 45 0 5 Km 52 Gam m art In the fraction < 2µm, Group 1 is characterized by a relatively highest average metal concentrations Fe, 38 2-20µm Gha r El Melh 30 39 47 Lagoon 31 Pb, Zn, Ni and Cr. Most of the sites of this group are 22 40 N 48 Group1 23 32 41 in front of Mejerda river. 24 Kallat Al 33 Group2 And alous 16 25 49 1 9 17 42 34 Group3 2 10 18 26 3 11 35 43 Group4 In coarser grain size sediment (2-20 µm), Group 1 19 27 50 Me jerda River 5 12 6 36 Group5 7 28 contains an extended area of potential sources of Canal Kalij 21 44 51

29 37 45 0 5 Km 52 metals contaminants in the region, mainly Zn, Cu Gam m art and Pb.

38 20-63µm 47 Ghar El Melh 30 39 Lagoon 31 In grain size fraction between (20-63µm) there are 22 40 N Group1 48 23 32 24 41 Group2 Group 2 and 5 which form two areas: the northern Kallat Al 33 16 Andalo us 25 1 9 17 42 49 Group3 34 area (lowest metal average) and the southern one 2 10 26 18 3 11 35 Group4 43 50 19 27 (high metal average). Mejerda River 5 12 6 28 36 Group5 7 21 Canal Kalij 44 51 29 37 45 0 5 Km 52 Gam mart Fig7: Classification of the sites based on the cluster analysis Conclusion

Trace element reflects mining in the gulf of Tunis.

In the different fractions <2µm, 2-20µm and 20-63µm traces elements are associated to hydrogenous fraction from water source outlet.

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

Trace element areal accumulations are clearly Distinguish according to their grain size fractions by cluster analysis in coastal sites in front of Ghar el Melh lagoon and in front of Mejerda River.