Changes of nutrient salts deposited in the burullus lagoon, egypt: Effects of human activity over the past century

：Burullus Lagoon is a a high，closed lagoon at the mouth of the Nile River，whose nutrients were mainly from the Nile. It is a critical area for studying how the changes in the Nile Basin has affected the lake environment of the Nile estuary after the Aswan Dam was built. This study investigated the changes of²¹⁰Pb dates，grain size，total or⁃ ganic carbon（TOC），total nitrogen（TN），total phosphorus（TP）and biogenic silica（BSi）in the B1 core from Bu⁃ rullus Lagoon，combined with historical data，to reveal the changes of nutrient salts in estuarine lakes and the impact of these changes on the ecological environment following construction of the Aswan Dam. The results showed that： （1）The content of depositional TOC，TN and TP increased from bottom to top，indicating that although the Aswan Dam led to a sharp decrease in nutrient flux，the TN/TP concentration in the downstream lakes did not decrease due to the greatly increased TN/TP flux discharged by human activity downstream of the dam. Also，TN/TP was less than 16，indicating that the lake was still P-restricted.（2）However，BSi and BSi/TOC generally decreased from bottom to top，indicating that the reduction of water and sediment caused by the Aswan Dam has led to a decrease in the bio⁃ mass of diatoms and the ratio of total primary productivity in the lake. The ecological environment of the lake tends to be deteriorating.