Relationship of salinity, temperature, pH, and transparency to dissolved oxygen in the Bouregreg estuary (Morocco): first results

Dissolved oxygen (DO) concentration is an essential indicator for assessment of estuary ecosystems. According to our knowledge, there is no research on the depth profiles of the DO and associated water quality variables of the entire Bouregreg estuary (Morocco). Water samples were collected from three stations at 0.5-m depth intervals during high and low tides (10/11/2021, 20/03/2022, and 02/07/2022). Our study shows that the DO concentrations ranged between 5.5 and 11.8 mg/l and demonstrated an inconsistent stratification pattern. When the tide was high and low in most of the study area, the bottom layer had a higher concentration of DO than the surface layer. There was a relatively high concentration of DO in the bottom layer of the estuary and a relatively low concentration in the surface layer of the estuary due to a high rate of freshwater flow on the surface (the release of Sidi Mohammed Ben Abdellah dam and the existence of estuarine gravitational circulation). Salinity, pH, water temperature, and water transparency ranged from 19.4 to 35.8 ppt, 7.0 to 8.7, 17 to 23 & DEG;C, and 16 to 21 cm, respectively, considering the depth profiles in the study area. The study provides scientific support for ecology operation and considerable advances in understanding the ecosystem dynamics of the Bouregreg estuary.