Classification of Spatial Variation Pattern for Identifying Pollution Sources: A Case Study on Sediment Contamination in Bizerte Lagoon, Tunisia

Mitsuo Yoshida 1 and RPP-SEPMCL2002 Shipboard Scientist Team 2
1 Institute for International Cooperation, Japan International Cooperation Agency (JICA)
10-5, Ichigaya Honmuracho, Shinjuku-ku, Tokyo 162-8433 JAPAN
Tel.: + 0081 3 3269 3851; Fax: + 0081 3 3269 6992
Yoshida.Mitsuo.2@jica.go.jp
2 Institut National de Recherche Scientifique et Technique (INRST)
B.P. 95, 2050 Hammam-Lif, TUNISIA

Abstract
The concentration of potentially toxic elements (PTEs) was measured for a total of 180 sediment samples collected from the Upper  Layer (surface sediments) and the Lower Layer (sediments repository) of lagoon bottom sediments distributed in the Bizerte lagoon, Mediterranean coast, northern Tunisia. The spatial variation pattern of PTEs contamination in the lagoon bottom sediments is classified into three types, Type I, II, and III. (i) Type I: A ‘peak’-shaped very high concentration part limitedly appears at several shoreline sites nearby the Menzel Bourguiba industrial zone. The  other sites show relatively homogeneous distribution with low concentration values.  This variation pattern implies that the contamination is caused by an effluent from the industrial zone, and the contamination has not widely spread toward the lagoon basin. Twelve elements are found in this type: Sb, As, Ba, Cd, Cu, Pb, Mo, Se, Ag, Tl, U, and Zn. Three heavy metals, Ba, Pb, and Zn, and two metalloids, As and Se, show toxic level of values above the regulation. (ii) Type II:  A ‘plateau’-shaped high concentration zone is present from south western part (Menzel Bourguiba, Tinja, and its north) to the west central part of the lagoon basin. The concentration significantly decreases eastward, southward, and northward. This ‘Plateau’ type pattern implies that the pollution source is the south western side of the lagoon, and the contamination migrates towards the central part of the lagoon. Seven elements are found in this pattern: Al, Cr, Co, Fe, Mn, Ni, and V. The concentration of five metals, Al, Cr, Co, Mn, and V, indicates above or around the criteria. (iii) Type III: The Hg concentration shows unique spatial variation of which higher values appear only near the south eastern shoreline of the lagoon basin. The Hg contamination is probably due to agricultural chemicals such as pesticides derived from the eastward-southward agricultural zone.

Keywords: sediment contamination, lagoon, potentially toxic elements, spatial variation

In: Caetano, M. and Painho, M. (eds). Proceedings of the 7th International Symposium on Spatial Accuracy Assessment in Natural Resources and Environmental Sciences, 5 – 7 July 2006, Lisboa, Instituto Geográfico Português

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