Chapter One
On Knowing the State of the Bay

Priority Eleven: Dissolved Oxygen (DO)

Dissolved oxygen (DO) is generally high throughout the bay, averaging near saturation through large areas of open water. Exceptions to this are in poorly flushed tributaries subjected to runoff inflow and waste discharges. A remaining problem area is the upper Houston Ship Channel, which has improved from essentially zero dissolved oxygen twenty-five years ago, to levels that support an improving living community of fish and other organisms. In the upper Houston Ship Channel, oxygen remains most depleted in bottom waters.

 Ward and Armstrong (1992) have provided the most complete description of water quality status and trends characterizing dissolved oxygen conditions in Galveston Bay. In the Houston Ship Channel above Morgan's Point, deficits in dissolved oxygen (the increment below saturation level) range to seven parts per million. The concentration has been improving over the last two decades at about 0.1 mg/L/yr in the worst areas near the turning basin, and at a higher rate downstream nearer the open bay. Oxygen-demanding pollutants (BOD) remain highest in the upper Houston Ship Channel, but are declining commensurate with the improvement noted in DO levels.

 The bay's western, urbanized tributaries (e.g. Clear Lake, Buffalo Bayou) also remain problem areas. These waters receive the bulk of the bay's nonpoint source pollutants in runoff, and have the greatest frequency of fish kills related to oxygen depletion-particularly in areas with poor circulation. The DO deficit near the outlet of Clear Lake is increasing, in contrast to the improving trend in much of the estuary. On a smaller scale, marinas, particularly in Clear Lake, have clear localized problems associated with boat sewage and other wastes (see Problem 13).