Aluminium in the South-eastern Mediterranean Waters off the Egyptian Coast

Abstract

Seasonal and spatial distribution of dissolved and particulate aluminium (Al) in the coastal waters overlying the continental shelf in the south-eastern Mediterranean waters off the Egyptian coast (29°45′E–33°30′E) were studied. Dissolved silicon (Si), and dissolved and particulate iron (Fe) were also studied simultaneously. Elevated concentrations were recorded in the inshore waters affected directly by the continental runoff and indirectly by the circulation pattern in the area.The concentration of dissolved Al varied from 0·021 to 0·732 and 0·003 to 0·127μmol in the nearshore (<50m depth) and offshore waters, respectively, while particulate Al ranged between 0·025 and 3·35, and 0·012 and 0·096μmol in the corresponding zone, respectively. The distribution of Fe seemed to be in parallel with Al. The concentration of dissolved Fe varied from 0·009 to 0·244 and 0·001 to 0·041μmol in the inshore and offshore waters, respectively. Its particulate form varied from 0·0001 to 1·66 and 0·01 to 0·22μmol in the corresponding zones, respectively. The concentrations of both metals in the particulate form are highly variable ranging from about 26 to 95% for both Al and Fe, and the particulate species are mostly abundant. Variations in the Fe/Al ratio probably reflect the horizontal transport and flux of Al from the different land-based sources, and the condition of the area. The atmospheric flux of Al represents about 75% of the present load. The predicted values of the freshwater end-member was calculated from the relationship with salinity, and estimated to be at 10m depth and 15km seaward.