GEOCHEMISTRY OF MAJOR AND MINOR ELEMENTS FROM SUR- FACE SEDIMENTS OF LAKONIKOS GULF, GREECE

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1 GEOCHEMISTRY OF MAJOR AND MINOR ELEMENTS FROM SUR- FACE SEDIMENTS OF LAKONIKOS GULF, GREECE Karageorgis, A.P., Kanellopoulos, Th.D., Papageorgiou, A., Taxiarchi, M., Kambouri, M. Institute of Oceanography, Hellenic Centre for Marine Research, Abstract The Gulf of Lakonikos is a relatively unexplored marine area in SE Peloponnissos, which receives freshwater from Evrotas River. In order to investigate potential anthropogenic impacts in the area, a grid of twenty-nine surface sediments were recovered from the northern sector of Lakonikos Gulf from shallow waters up to 200 m depth. Sediments were analyzed for their grain-size properties as well as for major and minor elements, which were determined with X-ray Fluorescence methods. The seabed of the Gulf is covered by sandy sediments, which gradually become finer towards the deeper waters. The spatial distribution of major and minor elements and also their ratios relatively to Al revealed that the coastal sediments are rich in Si, probably originating from excess detrital quartz. Heavy metal contents present low values suggesting that the area is unaffected by anthropogenic activities, at least as far as it concerns inorganic pollutants; however, this argument would be strengthened if local pre-industrial sediment was made available for the calculation of enrichment factors. Correlation analysis showed that the majority of the elements have terrigenous origin, i.e. aluminosilicate minerals, except for Ca and Sr, which represent the autocthonous biogenic fraction. Keywords: geochemistry, sediment, heavy metals, Lakonikos Gulf, Greece. 1. Introduction The Gulf of Lakonikos is located in the SE Peloponnissos and the study area concerns its northern sector, where water depths are generally less than 200 m. The Lakonikos Gulf is a N-S asymmetric graben, with a tectonic horst occurring within (Papanikolaou et al., 2001). The Gulf receives freshwater from the Evrotas River (catchment area 2,825 km 2, major branch length 82 km) and also from smaller rivers, e.g. the Vasilopotamos R. The Evrotas River drains mainly limestones and dolomites, metamorphic formations, flysch, marl sandstones and conglomerates, as well as recent Pleistocene-Holocene alluvial deposits. In the coastal area a long (~15 km) sandy beach prevails, and the coastal plain belongs to NATURA network protected areas. A few small towns and ports are situated along the coast, from west to east Gytheio is the largest port (population ~5000), Ai Giannakis fishing port, and Elia port (Fig. 1). The industrial activities in the area are very few; the most important include juice factories, a slaughterhouse, a meat processing factory, and mostly oil-mills and oil factories. In terms of pollution sources, except for the aforementioned agricultural activities the untreated domestic effluents are the most important. A previous comprehensive oceanographic study in the area (HCMR, 1992) showed that the Gulf is unaffected by the various human activities as far as it concerns heavy metal enrichment. The aim of the present work concentrates on the study of surface sediments grain-size, their geochemistry and element interrelationships, as well as the identification of the current status of the Gulf in terms of potential heavy-metal pollution. 2. Methods A set of 29 surface samples were obtained from the northern sector of the Lakonikos Gulf during June 2008 (Fig. 1). Sampling stations coordinates and water depths are shown in Table

2 9 th Symposium on Oceanography & Fisheries, Proceedings, Volume Ι 2.1 GRAIN-SIZE ANALYSIS Sediments were wet-sieved through a 63 µm sieve in order to separate the sand fraction. The remaining silt and clay fractions were analyzed in the Micromeritics Sedigraph 5100 X-ray analyzer, and subsequently silt and clay weight percentages were calculated. The sediments have been classified according to Folk (1974) (Table 1). 2.2 GEOCHEMISTRY OF MAJOR AND MINOR ELEMENTS Major elements were determined in fused beads and minor elements in pressed powders. The analysis was performed in a Philips PW-2400 X-ray wavelength spectrometer equipped with a 3 kw Rhodium tube. The preparation of fused beads where as follows: 0.5 g of sample were mixed with 5.5 g of flux (67:33 Lithium Meta-Borate, Lithium Tetra-Borate), 0.5 g of Lithium carbonate, and 0.5 g of ammonium nitrate. A few drops of LiBr were used as non wetting agent. The fusion took place in Pt crucibles and moulds, in a Claisse device. Pressed powders were prepared using 5 g of grinded sediment, well mixed with 1.5 g of wax (Hoechst Wax-C). The mixture was pressed in a 31 mm Al cup (20 ton, 20 s) employing a Herzog HTP-40 hydraulic press. Minor elements were determined using the Pro-Trace software of Panalytical, which uses a special set of 25 multi element high precision standards for calibration. Fig. 1: Study area location and sampling stations grid. 3. Results and discussion Grain size analysis results (Table 1) showed that the sand content varies significantly in the Gulf sediments (Fig. 2). Higher sand values are present in the near-shore sampling stations, especially in the NW part of the Gulf (maximum value 96.7% at station L2), whilst lower values (<10%) are present offshore (minimum value 0.03% at station L4). Reversely, fine sediments (silts and clays) predominate in the deeper part of the Gulf, and mainly lower than the 20 m isobath. Summary statistics for major and minor elements in the surface sediments of the Lakonikos Gulf are presented in Table 2. Calculation of correlation coefficients between major and minor elements distinguished three element groups: (a) Si; (b) Al, Ti, Fe, K, Na, Mg, P, Mn, V, Cr, Co, Ni, Cu, Zn, and Pb; and (c) Ca and Sr. Silicon values in the Lakonikos Gulf sediments are rather high (max 35.4%), whereas Si/Al ratio (Fig. 2) exhibits values up to 10, much higher than 3 which is the mean Si/Al value in marine sediments (Turekian and Wedepohl, 1961; Bostroem et al., 1972). The high Si/Al ratio together with the high correlation coefficient between Si and sand content (r = 0.875), imply that Si is related to terrestrial input of quartz. The spatial distribution of Si/Al ratio is fairly similar to the sand distribution, with increased values in the shallower sampling stations and decreased values (<2) in the southern -224-

3 Table 1: Sampling sites location, grain size distribution and sediment classification (Folk, 1974). Station Longitude Latitude Depth (m) Sand (%) Silt (%) Clay (%) Classification L muddy sand L sand L mud L mud L mud L mud L clayey sand L clayey sand L sandy mud L silt L mud L mud L mud L mud L mud L sandy silt L muddy sand L sandy mud L silt L silt L mud L mud L mud L sandy silt L silt L sandy mud L muddy sand L sandy mud L sandy silt stations (Fig. 2). Zirconium, though moderately correlated with Si (r = 0.514), seems to follow the distribution of the latter and, thus, we may add it in the group of terrigenous, coarse-grained fraction. Besides, zirconium is probably in the form of heavy mineral zircon (Zr[SiO 4 ]). Table 2: Summary statistics (min, max, standard deviation, mean, and median) for major/minor elements in surface sediments from the Lakonikos Gulf (n = 29). Element minimum maximum SD mean median Si Al Ti Fe K Na Ca Mg

4 9 th Symposium on Oceanography & Fisheries, Proceedings, Volume Ι Element minimum maximum SD mean median P V Cr Mn Co Ni Cu Zn As Sr Zr Pb The second element group represents clearly the terrigenous fine-grained aluminosilicates. Correlation coefficients of Al against all elements are high, e.g. Al:Mn r = and for many elements the relationship is almost linear (r > 0.950). Elements of this group are negatively correlated to sand values. The spatial distribution of Al (Fig. 2) follows the increase offshore percentages of the silt and clay component. This is a common distribution pattern, where particle size decreases with depth, as coarser material settles nearshore and finer silt and clay particles settle in deeper waters, where wave and current activity decreases. The spatial distribution of V/Al, Mn/Al, Co/Al, Ni/Al, Cu/Al, Zn/Al, As/Al, and Pb/Al increase with depth, showing their relationship with aluminosilicate minerals (e.g. Cu/Al and Zn/Al; Fig. 2). Elements of the third group (Ca, Sr) are exceptionally well-correlated (r = 0.938) revealing their common origin, i.e. biogenic carbonates. Ca and Sr are common substitutes due to their similar ionic radii (Broecker and Peng, 1982). Calcium spatial distribution patterns show values increasing from Fig. 2: Spatial distribution of sand dry weight %, Si to Al ratio, Al dry weight %, Cu and Zn ratios to Al (x10-4 ) and Ca dry weight %

5 the western sector of the Gulf towards the east (Fig. 2). Comparison between the spatial distribution of various elements (i.e. Fe, Mn, Cr, Ni, Zn, Co, Cu, and Pb) between this study and a previous one by Voutsinou et al. (1992) showed that the general pattern of higher values in the deeper sectors of the Gulf is predominant in both cases. These findings suggest that during the past decades the Gulf has not been affected by human activities, although agriculture has been more intensive and some industrial units have been installed. Nevertheless, the area could be affected by organic pollutants, i.e. pesticides and fertilizers used in agriculture. In order to better elucidate the possibility of heavy metal enrichment, it is recommended to use enrichment factors, using as reference local pre-industrial sediment (Loring and Rantala, 1992). Since such sediment was not available from the Lakonikos Gulf, we used a deep core sediment from the neighboring Messiniakos Gulf as reference; the estimated enrichment factors were ~1 for all heavy metals determined. 4. Conclusions The geochemical analysis of the northern Lakonikos Gulf sediments showed that the distribution of major and minor elements is mainly controlled by the grain size of the sediments, while the Gulf is generally unaffected by any human influence. The agricultural activity in the adjacent plain, the Evrotas River discharges as well as the small streams inputs in the area, have insignificant impact in the marine environment, in terms of potential heavy metal enrichment. Similarly, the domestic effluents of Gytheio town and other smaller settlements do not contribute to heavy metals in the Gulf. However, it is possible that the morphology of the Gulf and wind-driven SE prevailing currents (HCMR, 1992) may contribute to the removal of any minor anthropogenic-induced material to the open sea. 5. References Bostroem, K., Valdes, O. & Riera, M., Geochemical history of South Atlantic Ocean sediments since late Cretaceous, Marine Geology, 12: BROECKER, W.S. & PENG, T.H., /Tracers in the Sea/. Columbia Univ., 690 pp. FOLK, R.L., /Petrology of sedimentary rocks/. Hemphil Publ. Co., Austin, Texas, 182 pp. HCMR, Oceanographic study of the Lakonikos Gulf. Friligos (Ed.), HCMR Technical Report, 111 pp (in Greek). Loring, D.H. & Rantala, R.T.T., Manual for the geochemical analyses of marine sediments and suspended particulate matter. Earth Science Reviews, 32: Papanikolaou, D., Metaxas, C. & Chronis, G., Neotectonic structure of the Lakonikos Gulf. Bulletin Geological Society of Greece, 34 (1): Turekian, K.K. & Wedepohl, K.H., Distribution of the elements in some major units of the earth s crust, Geological Society American Bulletin, 72: Voutsinou, F., Georgakopoulou-Grigoriadou, E., Psillidou-Giouranovits, R., Fragoudaki, S. & Ladopoulou, M., Geochemistry of surface sediments in the Lakonikos Gulf. p In: /Oceanographic study of the Lakonikos Gulf/, N. Friligos (Ed.), HCMR Technical Report (in Greek)