Seasonal variation of physicochemical and bacteriological parameters of the coastal waters of the southern area of Monastir Bay affected by urban discharges

To evaluate the impact of anthropogenic activities and climate change on the water quality of Monastir Bay, monthly monitoring of physico-chemical and bacteriological parameters was conducted out in eight stations located in the southern part of the coastal waters during 2019. The obtained results showed severe fluctuations, both spatially and temporally, in temperature (from 9 °C to 33 °C), salinity (between 37.9 and 45.9 practical salinity units (psu), turbidity (between 0.18 and 8.5 nephelometric turbidity units (NTU), and pH (8.11 and 9.15). Oxygenation is quite variable, with total or partial anoxia recorded in certain areas of the bay, especially in the end of spring and in summer. Organic nitrogen and phosphorus concentrations were significantly higher in the North Bay than in the South. Mineral nitrogen at most stations was dominated by ammonium, indicating an imbalance in the nitrogen cycle. Chlorophyll a concentrations were above 20 µg/L in some stations, with two peaks, one in spring and a second in autumn. The bacteriological analysis showed a predominance of salt-tolerant bacteria and the presence of fecal contamination, especially near urban wastewater discharge zones. Analysis of variance confirms that this ecosystem is strongly influenced by anthropogenic inputs. The trophic index shows that more than 30% of the samples analyzed correspond to eutrophic waters. The high anthropogenic inputs combined with the limited current are responsible for the degradation of this ecosystem. The results obtained in this study constitute a database for the development of an ecological restoration strategy.