Phosphorus species in lake qarun sediments, a closed salty egyptian basin in the arid zone

The present Lake Qarun is an enclosed salty basin lying in the arid zone in the western desert of Egypt. Two peninsulas divide the lake into the eastern shallower basin and the western deeper basin. The lake water level, depending on the feeding drainage waters and evaporation rate, controls its area and volume. The distribution of phosphorus species in the lake sediments was studied for the first time to throw light on their contents in the sediments, as autochthonous phosphorus source.

The results of loosely sorbed phosphorus (NH₄ Cl-P), iron plus aluminium bound phosphorus (NaOH-P), calcium-bound phosphorus (HC1-P), organic and total phosphorus indicate that lake sediments were highly variable with respect to these parameters. The inorganic phosphorus (IP) was the abundant form adsorbed onto sediments. The NaOH-P was the most dominant species of the IP form. The highest contents of the three IP species were found in the southern lake region (NH₄ Cl-P) and in the middle region (NaOH-P) and in the northern region for the HC1-P. The highest values were found in the eastern with respect to NH₄ Cl-P and in the western for both NaOH-P and HC1-P. The horizontal distribution of IP showed a gradual decrease from south to north and from east to west, reflecting the importance of external loading and the nature of sediments favored the accumulation of phosphorus in the lake bottom. The increase in organic phosphorus (OP) in the southern and eastern regions reflects the remarkable increase in their fertility. Statistically, OP was highly correlated with different organic constituents and clay content of the sediments. The pattern of total phosphorus (TP) distribution illustrates that sedimentary TP was highly dependent on the TP in the lake water. The statistical associations indicate that IP and TP are dependent upon local sediment characteristics.