Evaluation of the standing crop phytoplankton in some coasts of Alexandria, Egypt

ABSTRACT

The hydrographic conditions and phytoplankton communities of the four regions, namely, El-Agami, Kayet Bey, the E. H. And El-Shatbi were studied monthly from June 1991 to May 1992 in relation to the inland run off of sewage effluents and industrial wastes in the three latter regions, which create eutrophic conditions. The polluted regions of Kayet Bey, the E. H. and El-Shatbi are characterized by lower salinity, low dissolved oxygen, while the dissolved organic matter, total alkalinity and nutrient salts remained high and this was associated with high density of phytoplankton. On the other hand, El- Agami region which lies faraway from the effect of sewage pollution harbored lower density of phytoplankton which appeared more diversified. The phytoplankton composition in the investigated areas comprised 140 species, belonging to Bacillariophyceae [85], Dinophyceae [27], Chlorophyceae [14], Cyanophyceae [12], one Silicoflagellate and one Euglenophyceae. Although the communities were diversified by numerous species but the few of them formed the main bulk of the standing crop and these comprised Skeletonema costatum, Nitzschia closterium, Spirulina platensis and Asterionella japonica. The phytoplankton standing crop in Kayet Bey region attained higher density [105, 233 units L-1] than the other two polluted of the E. H. and El-Shatbi [70, 237 and 17, 443 units L-1] impacted by the highest amount of discharge of sewage water, while the minimum density was recorded at El-Agami region. Also, the seasonal variations of the phytoplankton communities in the polluted regions, controlled with the seasonal variations of the physicochemical conditions and they were more correlated to the amount of inland discharge. Generally, the present study indicated a high level of eutrophication, particularly at Kayet Bey due to the impact of big amounts of sewage effluents discharged into the area and they are usually loaded with high concentration of nutrient salt. Also, the richness in species was inversely proportional to the standing crop and the lowest number was recorded during the bloom times. Also, the dominant species all above consider as indicator for eutrophication and pollution, although the standing crop of phytoplankton was low compared to the other areas. It was recommended that sewage wastes must be treated before discharge into sea