Impact of drain water on water quality and eutrophication status of Lake Burullus, Egypt, a southern Mediterranean lagoon

Abstract

The ecological and biological status of Lake Burullus was examined in 2006 to determine its water quality and eutrophication status in response to the quality and quantity of drain water entering it. The lake suffers from excessive nutrient concentrations. Chlorophyll a showed wide variations over the sampling period with maximum levels (85–122 mg m⁻³) in the western part in response to the nutrient-rich water inputs from the surrounding farmlands. Nutrients were at maximum levels in the southern and western parts of the lake, which were affected by wastewater discharged into the lake through the drains system. A dense (up to c. 8 × 103 cells ml⁻¹) and more diverse phytoplankton community (about 160 taxa) was found, with a four- to eight-fold increase in species abundance compared to that over the past two decades. Low Secchi transparency (0.15–0.50 m) and high total suspended matter were recorded when phytoplankton was abundant. According to the trophic state index, Lake Burullus could be classified as hypereutrophic with bad to very bad environmental conditions. A degree of nitrogen (N) limitation was recorded, possibly favouring N-fixing cyanobacteria, amongst which toxic species can exist. Lake restoration is recommended through drastic reduction of the external N and phosphorus loads by regulating effluents from fish farms and domestic and industrial sources.