Seasonal variations in physicochemical and nutrient parameters of Apalachicola Bay, Florida, and their implications to estuarine water quality and ecosystem health

This study investigated seasonal variations in physicochemical and nutrient parameters in Apalachicola Bay, Florida to determine their impact on the quality of estuarine water. In winter and spring 2024, water samples were sampled using 14 georeferenced sites. Water samples were measured in place where the temperature, dissolved oxygen (DO), pH, salinity, turbidity, specific conductance (SC) and the total dissolved solids (TDS) were measured, whereas ammonium, nitrate, and phosphate were analyzed in the laboratory. The results showed that water quality varied significantly between seasons, with higher salinity (0.070–28.50 ppt vs. 0.05–13.4015.87 ppt), temperature (28.25–29.51 °C vs. 13.40–15.87 °C), and specific conductivity (0.130–44.27 mS/1 cm vs. 0.09–11.78 mS/1 cm) were greater in spring compared to winter (p < 0.05). The concentrations of nutrients demonstrated a clear seasonal distribution, with nitrate levels of 0.99200 mg/L in winter and 0.14214 mg/L in spring, and ammonium levels of 0.0051.73 mg/L in winter and 0.041.73 mg/L in spring, having a site-specific distribution. Phosphate was below the limits of detection in several sites during winter but was consistently detected during spring (0.00120.517 mg/L). The turbidity was consistently greater than the standards of the U.S Environmental Protection Agency (5 NTU), especially in the winter (2.21 - 41.50 NTU). Water quality was classified as poor in both seasons with the winter at a CCME WQI of 30.25 and spring at 17.59 and shown to have guideline breaches on a large scale, especially on dissolved oxygen, specific conductivity, turbidity, and nutrient parameters. Correlation analysis showed a strong positive relation between the parameters of ionics (r = 0.995–0.999, p < 0.001) in both seasons with seasonal changes in nutrient-sediment relations. The findings indicate that Apalachicola Bay is susceptible to eutrophication and that it needs extensive monitoring and spatially sensitive watershed management measures to accommodate high salinity, TDS, turbidity, and nutrient loads especially in spring.