Anthropogenic pressures reshaping the ecosystem of Burullus lagoon (Nile Delta): Diatom evidence of post-Aswan Dam perspective

The Nile Delta is extremely vulnerable due to scarce freshwater input under an arid climate setting. Lagoonal eco-setting has been aggravated by remarkably low sediment and water from the Nile River, but high wastewater discharge since the Aswan High Dam was emplaced in 1964. The ecological response in such environmentally-restrained lagoons has gained increasing global concern. This study thoroughly examines the spatial distribution of diatom communities in Burullus lagoon, aiming to track post-dam drivers behind. Multiple geo-biological approaches were used to analyze sediment-water samples covering the entire lagoon. Ecological affinity of diatom saw two diagnostic assemblages: the I at western lagoon and two ends with purely freshwater/marine species; and the II at eastern lagoon with mixed brackish species. While the muddy sediment had a good preservation of diatoms, higher abundance and diversity were recorded at the lagoon ends. Freshwater species of the western lagoon were correlated with higher anthropogenic discharge. This is manifested by the dominant Stephanocyclus meneghinianus , associated with the organic carbon-rich habitat there. Water pollution has also screened out pollution-tolerant freshwater species, represented by Navicula aegyptiaca . Marine-brackish communities, noted as Podosira stelligera , were dominant in the northeast-central lagoon, reflecting much seawater introduced recently into the lagoon via a hydro-engineering project. Our data further suggested that both higher chlorophyll a and total alkalinity, vs. lower diatom abundance in the central lagoon, imply algal blooming resulted from other phytoplanktonic populations, rather than diatoms. Moreover, eutrophication has led to diatom communities with more pennate species of benthic and epiphytic nature in Burullus. The quantitative relationship established between altered diatom communities and anthropogenic forcings provides countermeasures against challenges from environmental stresses.