Long-term evaluation of eutrophication problem using multi-sensor satellite data along El-Max Bay, Alexandria coast and Abu-Qir Bay, Egypt

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Abstract

The Alexandria coastal water and Abu Qir Bay are subjected to Spatio-temporal variations in their primary productivity and physical-chemical properties both on a short and long-term basis because of continuous and ever-increasing discharge of organic and inorganic from urban supplies and sewage collection systems.
Chlorophyll-a (Chl-a) concentration, expressing phytoplankton biomass, is considered a good indicator of the water's trophic state. In the present study, the average daily, monthly, seasonal, and annual means of reading of Chl-a were obtained between 2000 and 2019 from multi-satellite sensors to characterize the Spatio-temporal variation of phytoplankton in the Egyptian coastal area.
 Our results showed that phytoplankton anomalies varied spatially and temporally. The study recorded a remarkable increase of Chl-a during the period from May to September (spring and summer) each year, summer readings were higher than spring. Annual Chl-a data showed an upward tow trend, the first was from the year 2000 to 2010, the second and the highest trend was from 2011 to 2019, occurs after the revolution of January 25, 2011. Overall, the study period of Chl-a reaches its maximum values (35 mg/m3) during 2015 at Abu Qir Bay and 40 mg/m3 at El-Max Bay during 2019. The Chl-a concentration was high and more pronounced near the outlets of the Egyptian coastal lakes and urban outfalls, especially at El-Max Bay and Abu Qir Bay compared to the Alexandria shore area. There was a very low positive correlation between the Chl-a and sea surface temperature (SST), on the other hand, the correlation between Chl-a and the diffuse attenuation coefficient KD_(490) seems to be strongly positive and it was strongest with Colored dissolved organic matter (CDOM), as well as the correlation between Chl-a and nitrate and phosphate was strongly positive.

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