Title : Impact of restoration project on water quality and macrophytes biodiversity of nile delta lake manzala, Egypt
Abstract:
Shallow lakes shift rapidly from clear-water conditions with abundant submerged aquatic vegetation to turbid-water conditions, dominated by phytoplankton, with poor water quality. Therefore, native vegetation in those lakes is severely degraded worldwide. Lake Manzala showed decrease in its water surface to 385 km2 in 2013. Evaporation due to rise in temperatures, globally, in addition to evapotranspiration caused by the increased area of water hyacinths and pollution hazards, all of which degrade the lake. Thus, detailed information about the long-term variability of aquatic plants, accompanied with water quality changes, can help investigate the potential driving mechanisms in order to mitigate the degradation. Seasonal long-term variability of macrophyte community structure in Lake Manzala was studied based on two periods: pre- and post-developmental planning, sustained by Egyptian Government in 2017. In addition, to the construction of a largest, Guinness recorded, waste treatment plant on the most and heavily polluted of all drains sources, Bahr El Baqar. Extinctions of native and/or excessive growth of macrophyte cause the biological diversity to descend, accompanied by heavy phytoplankton bloom. The free-floating vegetation Salvinia, Nympheae, Cyprus papyrus and other natives are extinct. Water hyacinths (Eichhornia crassipes) and water cress (Pistia stratiotes) were recorded in front of the heavily polluted drains from 2010 until 2022. The submerged grasses Echinochloa stagnina, Potamogeton pectinatus, the cattail Ceratophyllum demersum, and the cosmopolitan water nymphs Najas armata and N. flexilis were recorded in the middle-deepest part of the lake, known as the most productive area. Lake Manzala during years 2012, 13, 14, 15, and 16, i.e., pre-development, recorded the same vegetation as before, in addition to the water fern Azolla filiculoides and the perennial herb Runnunculus aquatilis (common water crowfoot) in front of polluted drains. This was accompanied with high organic matters, ammonia and low oxygen content, due to shallowness and high water temperatures. After the development project which started in 2017 and continued until 2021, water quality improved to moderate, while the community structure showed the presence of two free-floating species, four floating herbs, six submerged vegetation, and four emergent halophytes, in addition to one filamentous green alga, spreading along selected research locations. The submerged macrophyte, Potamogeton pusillus, and cosmopolitan Myriophyllum verticillatum were recorded in the vegetative part of the lake. They are capable of withstanding pollution hazards and acclimated to the changing quality of water. A newly recorded African aquatic subshrub, the creeping herb Alternanthera littoralis (red Hygrophila), the rhizome herb lakeshore bulrush, salt-tolerant Schoenoplectus lacustris sp., were recorded for the first time in front of polluted drains summer and winter 2019-2020. During 2022 still pollution indicators exist, waiting for renewable biodiversity with progress in wastewater treatment facilities.
