Assessment of Primary Production in an Estuarine Environment: The Case of the Oum Er Rbia Estuary (Atlantic Coast, Morocco)

Variations in primary production in relation to selected physicochemical and biological parameters of the Oum Er Rbia River estuary were measured monthly from November 2018 to January 2020 at two stations using the clear and dark bottle method. Gross primary production (GPP) ranged from 9.28 to 467.07 mg C/m3/h; net primary production (NPP) ranged from 3.09 to 248.13 mg C/m3/h; and respiration (R) ranged from 4.03 to 262.73 mg C/m3/h. GPP, NPP and R are lowest in summer, increasing to peak in spring. In summer and winter, significantly positive correlations were observed between GPP and NPP on the one hand, and phaeopigments on the other. In summer, there is also a significant positive correlation between respiration and dissolved oxygen concentration. In winter, significant negative correlations were found between conductivity and salinity, on the one hand, and GPP, and in summer and winter, on the other, with NPP. Spatial and seasonal variations in productivity depend on the environmental and meteorological conditions at each station, including water temperature, salinity, conductivity, nutrient inputs and light availability.