Benthic ostracods as environmental proxies in Nile Delta Coastal Lagoon

Abstract

The coastal Nile Delta wetlands are essential in the protection of the cultivated deltaic land against sea level rise and are major resources for biodiversity and fisheries productivity. The Manzala Lagoon ranks highly polluted among the lacustrine coastal environments of the Nile Delta of Egypt. The environmental quality of the lagoon plummeted a few decades ago with the increase in massive quantities of untreated mixed discharges (agricultural, industrial, and municipal). To evaluate the environmental status of the lagoon requires both geochemical analyses and bioindicators. Total organic carbon and concentrations of seven potentially toxic elements (Pb, Cu, Cd, Zn, Ni, Co, Fe) were determined in 25 sediment samples collected during summer 2014, from which three pollution indices were calculated (Contamination Factor, Degree of Contamination, and Pollution Loading Index). In addition, ostracod assemblages were assessed in the very-fine and fine sand-size fractions of the sediments. The lagoonal environment is characterized by low total dissolved solids, abundant organic matter, heavy metal contamination by Pb, Co, Ni, and especially Cd, and low diversity ostracod assemblages. Six fresh- and brackish water ostracod species were documented, but the assemblage was overwhelmingly dominated (>98 %) by stress-tolerant Cyprideis torosa. While this species correlated strongly with total dissolved solids and fine sediment textures, overall, the limited ostracod diversity and dominance of a stress-tolerant species reflects the compromised ecological quality of Manzala Lagoon.