Short-Term Variability of Nutrients and Fecal Indicator Bacteria within the Gold Coast Seaway, Southern Moreton Bay (Australia)

Significant urban development surrounding the Gold Coast Broadwater and upper catchment has resulted in concerns about degrading water quality of the estuarine system. The Gold Coast Seaway plays an important role in the exchange of estuarine and oceanic waters influencing the intertidal waters of the region. Water quality within the Gold Coast Seaway and the immediately adjacent Broadwater was investigated three times at three sample depths at 13 sample locations. Conductivity, temperature, and depth casts, total (nitrogen and phosphorus) and dissolved inorganic (NOx and NH4+) nutrients, and fecal indicator bacteria were measured at hourly intervals to compare the water quality under different tidal conditions at each location. Hydrological data were also collected. From these measurements, the intratidal variability of the Seaway waters was determined. Observed current velocities ranged from 0.001 to 0.909 m s(-1) and 0.018 to 1.8 m s(-1) during neap and spring tide periods, respectively. Physical parameters and nutrient concentrations demonstrated typical cyclic variations, with the influence of tidal and diurnal cycles apparent. Near minimum and maximum concentrations were generally observed at high and low water, respectively, indicating the influence of oceanic water during flood tides and catchment waters during ebb tides. Significant correlations were observed between surface water salinity values and total nitrogen and phosphorus concentrations. Fecal coliforms and Enterococcus spp. concentrations were low (<60 colony-forming units per 100 mL(-1)), with no significant trends apparent between concentration and sample location, depth, or tidal phase.