Assessment of Water Quality and Nutrient Dynamics in the Mediterranean Lagoon of El Mellah

Coastal lagoons are among the most productive yet vulnerable ecosystems worldwide, facing increasing pressure from human activities and climatic variability. This study evaluated the current physico-chemical status and organic pollution of Lake El Mellah, a Mediterranean lagoon in northeastern Algeria, to provide an updated baseline for environmental management. Water quality was assessed across 15 stations through monthly monitoring of temperature, pH, dissolved oxygen, and key nutrients (NO₃, NH₄, PO₄). Stream discharge and precipitation data were analyzed to interpret hydrological patterns. Results revealed strong seasonal contrasts, with winter rainfall and inflows sustaining higher water renewal, while summer stagnation promoted nutrient accumulation. Nitrate concentrations reached up to 62mg L⁻¹, reflecting agricultural influence, and orthophosphate levels peaked in summer, suggesting sediment release under low oxygen conditions. The organic pollution index indicated moderate to high organic loading, exceeding recommended limits for fishery waters at several sites. This study offers the first comprehensive, seasonally resolved assessment of Lake El Mellah’s nutrient and organic pollution dynamics, highlighting anthropogenic and hydrological drivers of eutrophication. Compared to previous work focused mainly on hydrobiology or biodiversity, this research integrates physico-chemical, hydrological, and pollution indicators, providing an essential reference for long-term monitoring and conservation of Mediterranean coastal lagoons.