Wastewater Discharge, Nutrient Loading, and Dissolved Oxygen Dynamics in a Shallow Texas Bay

In Oso Bay, a wastewater treatment plant acts as a source of eutrophication and may have measureable impact on the health of the bay. The objectives of this study were to create a model for modeling dissolved oxygen concentrations over time and to determine if eutrophication caused by the wastewater treatment plant is harmful to the bay. Continuous monitoring of environmental variables was carried out at 6 stations in Oso Bay over a 9-month period beginning in February and ending in December of 2013. Variables measured were water temperature (oC), pH, salinity (ppt), conductivity (mS), depth (meters), turbidity (nephilometric turbidity units), dissolved oxygen in both % saturation and concentration (mg/L), and chlorophyll-? concentration (?g/L). Grab samples of chlorophyll concentration (?g/L), total suspended solids (mg/L), and nutrient concentrations (?M) were also taken throughout the sampling period. Nutrients of interest were phosphate (PO_(4)), silicates (SiO_(4)), ammonium (NH_(4)), and nitrate+/-nitrite (NO_(x)). Hypoxia was observed at each of the stations in the bay and fluctuated on a diel cycle. Temperature, salinity, and temporal variability were significant factors in explaining the variance in dissolved oxygen concentrations (P < .0001) and were used to model dissolved oxygen variance (R^(2) = .7810). It is likely that the respiratory patterns of phytoplankton and bacteria also influence dissolved oxygen concentrations in Oso Bay, and that this is an indirect result of the discharge from the wastewater treatment plant.