Environmental Impacts on Egyptian Delta Lakes’ Biodiversity: A Case Study on Lake Burullus

The Nile Delta lakes are proximate reservoirs of the Nile water flowing to the Mediterranean Sea. They play an important role in the nation’s economy, not only because of producing more than 40% of the nation’s fish catch but also for being resting areas for migrating birds. Moreover, they have an ecological importance due to a variety of biodiversity inhabiting the lakes and their hydrologic attributes. The expansion of agricultural reclamation after 1950 led to an increase in the amount of agricultural drainage to reach more than 4,000 million cubic meters which caused shifting in the biodiversity of the Lake Burullus. Therefore, the levels of salinity in the Lake Burullus decreased to reach 4.01‰ in 2015 which led to the fact that the freshwater biota became more predominant in the food web of the lake. In addition, the levels of nutrients derived from agricultural drains to the water body of Lake Burullus increased especially after 2001. Despite the gradual increase in fish production in the lake from 7,549 tons in 1963 to about 63,000 tons in 2015, the environmental factors also affected the variety of fish production causing the fish production in the lake to shift from marine species to freshwater fishes, and therefore, the diversity of marine fishes declined in the lake such as Dicentrarchus labrax, which has declined from 2,375 tons in 1991 to 346 tons in 2014, and some of these species have disappeared such as Argyrosomus regius and crab. As a result, the fisheries were shifted from mullet-based fish (marine) to tilapia-based fish (freshwater), while the production of mullets in the lake was declined from 44.7% in 1963 to 15.9% in 2015. On the other hand, the production of tilapia sharply increased from 42.8% in 1963 to 72% in 1992 and then decreased to around 62.1% in 2015. Environmental conditions of Lake Burullus results an increase and more abundance of freshwater aquatic macrophytes species while reduction of other species to one or two populations with few individuals on the shores of the Lake.