Coastal water quality in the northern part of the Persian Gulf: spatial and temporal variations

The coastal swimming waters of Bushehr province in southern Iran, located in the northern region of the Persian Gulf, face persistent microbial and chemical contamination. This study aimed to evaluate the water quality of six beaches across five cities in Bushehr province. Water samples were collected, and physicochemical, microbial, and chemical parameters were analyzed following standard protocols. Nutrient concentrations, including nitrate, nitrite, phosphate, silicate, ammonia, total nitrogen, and total phosphorus, were found to range between 157.94 and 444.39 µg/L, 3.91 and 7.99 µg/L, 1.74 and 5.17 µg/L, 63.52 and 132.09 µg/L, 0.07 and 0.24 µg/L, 1158.00 and 2317.22 µg/L, and 39.57 and 59.49 µg/L, respectively. The mean concentrations of polychlorinated biphenyls (PCBs) varied seasonally, ranging from below the limit of quantification (< LOQ) to 0.98 ng/L in summer and < LOQ to 0.29 ng/L in winter. Microbial analysis indicated that the 95 th percentile values for total coliform, fecal coliform, and intestinal enterococcus bacteria ranged from 1080 to 1590 MPN/100 mL, 125 to 206 MPN/100 mL, and 12 to 49 CFU/100 mL, respectively, in the studied swimming areas. Based on the water quality index (WQI), these waters are categorized as "medium" quality, with WQI values ranging from 65.6 to 69.9. Multivariate analysis identified strong correlations between BOD, COD, intestinal enterococcus, total coliform, ammonium, and nitrate levels at Siadat Park, a site with untreated wastewater discharge and the highest recorded pollutant concentrations. Considering the high recreational activity at these beaches and the potential health hazards, implementing effective management and communication strategies is essential. Such measures would improve beach safety and reduce the transmission of waterborne pathogens. These findings provide a baseline for future research and offer guidance for management planning in coastal swimming areas of the Persian Gulf.