An input/output flux for lead in a coastal bay off Alexandria region

Abstract

During 1987, seawater, rain, dust and drainage water samples were collected from Abu-kir bay (360 km2) east of Alexandria city to set up and evaluate the relative importance of different sources to the biogeochemical cycle of Pb in the bay. The mean total concentration of Pb in the bay water was 455 ± 180 and 785 ± 287 ng kg−1 during low and high flow periods, respectively. About 75 ±12% are in the particulate form. The bay receives annually about 8.12 ± 2.18 and 6.13 ± 1.06 ± of Pb through agricultural and industrial discharge. In addition, 0.48 ± 0.11 ± yr−1 and 0.23 ± 0.04 t yr−1 of Pb reaches the bay through wet and dry depositions, respectively. The outflowing surface water from the bay carries 15.4 ± 3.6 t Pb yr−1 to the southeastern Mediterranean waters. Data from sedimentation traps indicated that the bulk sedimentation rate in the bay was 95 ± 18 kg yr−1 elevating the concentrations of Pb in sediments to more than 64 μg g−1. The imbalance in the Pb flux (excess + 0.6 ± 0.08 t) indicates Pb accumulation in the water column. The apparent residence time of Pb in the bay is 62 ± 15 d. The assimilative capacity of Pb in the bay expressed in terms of Pb loading / in bay concentration amounted to 25 ± yr−1/ μg L−1. A 10% reduction in the present day load to the bay will yield a Pb concentration of less than 0.1 μg kg−1 after 11 to 12 yr.