Figure 1 Map of Lake Mariout showing the sampling sites
Related Figures (8)
Table 1: The seasonal range, mean +SD and annual mean of physicochemical parameters of Lake Mariout Water during 2014. Salinity plays an important role in biological processes affecting algal blooms, fish movements, shellfish productivity, and aquaculture. Different Tilapia species can be adapted according to water salinity in the range of 5-49%o (Abdel-Fattah 2006). Decrease in water salinity enhances the flourishment of macrophytes to cover wide areas of the Lake (Mamdouh ef al. 2001). The present data revealed wide variation in the level of salinity content (Table 1). Minimum salinity values were 0.39 followed by 0.43 at Nubaria drain (drinking water canal) in spring and autumn seasons respectively. The maximum salinity values were 7.4%o0 followed by 7.12%o at station VII in spring and summer seasons (Fig. 2). The salinity annual average was 3.70%o0 + 1.69%o0 (Table 1). Generally, these low salinity values indicate that; the water content in Lake Mariout was mean content of ammonium was 15.61 + 15.46 uM (Table 1). Nitrite (NO2/N): A minor constituent of DIN represents from 0.04 to 8.99% of DIN and is characterized as intermediate compound which could oxid ation of ammonium or reduction of nitrate and can be derived either from the be removed from solution during nitrogen assimilation by phytoplankton. It is recommended for the highest uction of Tilapia that NO2/N concentration in water should not exceed 0.06 mg/l (0.02 mg/l of NO2 form) (Rachman and Adi 2005). According to the obtained data of nitrite concentration, it is noticed that most stations are not suitable for Tilapias prod prod uction. Nitrite concentrations differed between near de pletion (0.05uM) followed by 0.08, 0.1uM at station X in all seasons of 2014, and 22.48 uM followed by 19.83 uM at station V in summer and autumn, respectively (Fig. 4). Annual nitrite average was 3.4343.38 uM (Table 1). The lowest nitrite concentrations values were observed in winter, while the highest values were noticed in autumn followed by summer season. This is mostly due to the high rate of nitrification processes where the level of NH," concentration was inversely proportion to this relation during this period of otndat Table 2: Carlson’s trophic state index values and classification of lakes According to seasonally calculated TRIX and Carlson’s trophic state indice values, the sites are ranked in a descending order from very high to moderate eutrophi: evel in most stations as shown in (Figs. 6 and 7); revealing the existence o unthropogenic pressure.
