Time series relationships between chlorophyll-a, physicochemical parameters, and nutrients in the Eastern Harbour of Alexandria, Egypt

The Eastern Harbour of Alexandria, on the Egyptian Mediterranean coast, is characterized by environmental complications due to different types of anthropogenic stressors associated with water dynamics inside the harbor as well as the rapid water exchange with the open sea. These conditions caused chronic eutrophication conditions, with variable levels in the long term. The present study followed daily some physicochemical parameters, nutrients, and phytoplankton biomass, for a complete year. The results indicate coincidence on the short-time scale between the nutrients, phytoplankton biomass, pH, and dissolved oxygen. Spearman's correlation illustrated strong positive correlations between algal blooms and both pH and dissolved oxygen. The present study recorded twelve separate algal blooms, with an average of chlorophyll-a > 16.7 μg/L, confirming the continuity of high eutrophication in the Eastern Harbour. The seasonal Mann-Kendall tests showed that summer attained significant increasing trends for chlorophyll-a, silicate, nitrite, and nitrate, while winter has a significant decreasing trend for chlorophyll-a and pH.