A short-term water-quality study on Bayou Casotte and Bayou Chico on the Mississippi Gulf Coast was conducted on July 25-27, 1978. The results of the study indicated that the chemical and physical properties and range of concentrations of several dissolved constituents in both estuaries varied during a tide cycle primarily as the result of the interaction of freshwater and wastewater inflow with the saline Gulf waters.
The water quality condition of both estuaries generally was good and the low 5-day biochemical oxygen demand in the estuaries indicated that excessive oxygen demand was not exerted during the study. The 5-day biochemical oxygen demand generally was less than 3.5 milligrams per liter. Dissolved-oxygen concentrations decreased with depths and the lowest concentrations occurred below 30-foot depths in Bayou Casotte. Oxygen levels at shallow depths generally were less in Bayou Chico than in Bayou Casotte. Dissolved-oxygen concentrations in Bayou Casotte ranged from 0.7 to 7.7 milligrams per liter at high tide and from 2.5 to 8.2 milligrams per liter at low tide. In general, phosphorus and nitrogen species were present in comparatively high concentrations in both estuaries; were higher at low tide that at high tide; and were highest in Bayou Casotte upstream of Bayou Casotte harbor. Concentrations of the nitrogen species during a tide cycle generally were lower at the mouth of Bayou Casotte than at the mouth of Bayou Chico. Fecal bacteria at most sampling sites were generally in concentrations indicative of recent manmade pollution.
