Physical-Chemical Controls of Dissolved Oxygen in a Gulf Coast Estuary, 1994 Environmental Conference Proceedings

A. W. Niedoroda, C. W. Reed, T. W. Gallagher, J. H. Price

A three-step process was used to evaluate the factors controlling water quality in Perdido Bay. These steps were to: a) develop an understanding of the physical and chemical processes of the estuary, b) evaluate the loading from point and non-point sources in the system, and c) use water quality modeling to quantitatively relate the measured data and to provide interpretation of the relative scale of the loads from the whole system.

Because Perdido Bay is relatively small, with the major river discharge entering at its head, it provides an excellent representation of a shallow Gulf Coast estuary. The results show that the bay is nearly always density stratified in at least some of its sub-reaches. Its hydrography varies between three distinct patterns depending on both long-period and event-scale changes in the river inputs. The prevalent strong density stratification, elongation of the bay across the dominant strong wind direction, and limited diurnal tide range all serve to inhibit vertical mixing leading to frequent occurrences of low dissolved oxygen in the bottom waters of the bay at varying times throughout the year.