Spatio-temporal nutrients variability in the Oualidia lagoon (Atlantic Moroccan coast)

This work focuses on the water column biogeochemical cycle of the Oualidia lagoon (Moroccan Atlantic coast). The study of the biogeochemical cycle requires the evaluation of nutrients distribution, the factors controlling this process and their influence on different compartments of the lagoon environment. Water samples were collected fortnightly from March 2011 to August 2011, at six stations distributed throughout Oualidia lagoon. The physico-chemical parameters measured (temperature, salinity, dissolved oxygen) and nutrients (orthophosphate, nitrite and ammonium) showed seasonal and spatial variation with a gradient between upstream and downstream of the lagoon: diminution of the temperature, dissolved oxygen, nitrite, orthophosphate and ammonium and augmentation of the salinity throughout the lagoon. The highest nutrient values (NH4+ = 76.87 ?mol.l-1 to station S4, PO43- = 89.38 ?mol.l-1 to station S4, NO2- = 17.74 ?mol.l-1 to station S5) are generally from the middle to the upstream of the lagoon. Inversely the lowest values (NH4+ = 0.31 ?mol.l-1 to station S1, PO43- = 0.10 ?mol.l-1 to station S1, NO2- = 0.03 ?mol.l-1 to station S1) are located downstream, where the dilution of nutrient-rich originating in upstream (continental and vegetable crops inputs) are diluted by the high penetration of marine waters.