Changes in Sedimentary Biogenic Elements in the Burullus Wetland, Egypt: Impact of Human Activities Over a Century

Burullus, a highly enclosed wetland at the mouth of the River Nile, receives biogenic elements primarily from the Nile River and serves as an ideal area for studying how changes in the watershed, particularly since the construction of the Aswan Dam, have impacted the estuarine lakes' environment. This study aimed to reveal the differences in nutrient salt levels in the estuarine lakes before and after the Aswan Dam's construction, as well as addressing the effects of these changes on the ecological environment through 210Pb dating of Burullus Lagoon B1 cores, combined with testing and analyzing the total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and biogenic silica (BSi), alongside the historical data. Theresults showed that sedimentary TOC, TN, and TP contents generally increased from bottom to top. This indicatesthat despite the significant reduction in nutrient fluxes due to the Aswan Dam, nitrogen (N) and phosphorus (P) concentrations in downstream lakes did not decrease owing to the substantial increase in N and P inputs from human discharges downstream, and that sedimentary TN/TP ratios were all below 16, suggesting that the lakes remained phosphorus-limited. While, the biogenic silica (BSi) and the BSi/TOC ratio both showed a decreasing trend from bottom to top, indicating that the reduction of water and sediment caused by the Aswan Dam has led to a decline in diatom biomass and their overall contribution to primary productivity in the wetland, suggesting that the ecological environment may deteriorate over time.