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The Manzala Lagoon in Egypt's Nile ' »el-ta has become a sediment sink of reduced area and depth, with increased contaminant levels. Loss of much-needed fresh to brackish water reserves and decreased fish catches have serious ramifications. Herein, maps of temporal and regional sediment distributions in Manzala incorporate petrological and statistical analyses of 200 surficial and short core samples. These provide baseline information needed to help implement protection measures for this vital wetland. Four periods are considered: 1920s, 1940s, ~ 1965, and 1990. Important depositional changes between 1940s and ~ 1965 resulted from anthropogenic effects on this quasi-closed lagoon system, including industrial buildup, wetland conversion to agricultural land, and irrigation waterway development. Further modification from ~ 1965 to 1990 is associated with closure of the Aswan High Dam, continued construction of waterways that discharge waste water into lagoon margins, and marine incursion into the northern lagoon. If current practices continue, the lagoon could be reduced to about one-third of its present area by 2050 AD.

The concentration of rare-earth elements and yttrium (REY) was investigated in dissolved phase, suspended particulate matter, and seafloor sediments of the western coastal area of the Gulf of Thailand. The samples show Eu and Gd positive anomalies in the shale-normalized REY patterns, especially in the suspended particulate matter. On the other hand, a very high REE content was detected in the coastal waters, probably due to the weathering produced by the Mae Klong river waters on rare-earth element (REE)-rich accessory minerals coming from terrains and mineral deposits cropping out in the studied area. The shale-normalized patterns of yttrium and REE estimated for the dissolved phase show an enrichment of medium rare-earth elements (MREE), characteristic of extensive water-rock interactions and weathering occurring in the continental environment. The REE concentrations of suspended particulate, normalized to the REE concentrations in each sediment sampled from the tidal flat, show the same behaviour of the experimentally determined apparent REE bulk distribution coefficients [1] for pH values ranging from about 5.5 to 6.2. Since the REY concentration of the water masses is controlled by the oceanographic features of the studied area, riverine inputs, and ionic straight, we suppose that the dissolved phase represents a mix of truly dissolved and colloidal pool (<0.2 µm) in which REY were enriched during the rock-water interactions of continental environment. In the estuarine system, the salt-induced coagulation of colloidal pool takes place and an authigenic fraction of suspended matter is formed, assuming the typical REE behaviour due to rock-water interactions.

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