When it comes to the overall health of an aquatic ecosystem, the amount of dissolved oxygen (DO) in the water is a good indicator. DO not only allows fish and other aquatic organisms to breathe, but also plays a crucial role in the breakdown and decomposition of organic pollutants that find their way into our waterways. DO levels usually range from 3 to 10 milligrams per liter (mg/L), with most aquatic life requiring greater than 5 mg/L to maintain a healthy and diverse population. Some of the factors that affect DO concentrations include water temperature, water depth and flow rate, and the amount of organic material present in the water.
The waters around the Port of Stockton have had historically low DO concentrations. This is due in large part to the geometry of the Deep Water Ship Channel and the low flows in the San Joaquin River. In an effort to promote a healthier waterway, the Port operates and maintains an aeration facility at the confluence of the Deep Water Ship Channel (DWSC) and the San Joaquin River. In an effort to promote a healthier waterway, the Port operates and maintains two aeration facilities that are used to add oxygen to the DWSC when DO levels are low.
One facility is located at Dock 20. This facility was constructed in 2007 by the California Department of Water Resources and is maintained and operated by the Port of Stockton. Its purpose is to add oxygen to the DWSC during periods when oxygen levels are low, most often in the summer and fall. The facility is capable of adding approximately 8,500 pounds of oxygen per day. It works by pumping water from the DWSC, injecting it with pure gaseous oxygen, and then sending the water below ground to a depth of approximately 200 feet.
The oxygen gas dissolves into the water and the high pressure created at that depth makes it possible to dissolve more oxygen than would be possible at ground level. The highly-oxygenated water is then returned to the DWSC thereby raising the dissolved oxygen concentration upstream and downstream of the facility. By increasing dissolved oxygen levels in the DWSC, the Port helps maintain a healthy ecosystem for fish and other aquatic species that depend on oxygen for survival.
The other facility is located at Dock 13 at the confluence of the Deep Water Ship Channel and the San Joaquin River. The facility (pictured) consists of two jet aeration devices that dissolve atmospheric oxygen into the water at a rate of approximately 1,000 pounds per day. The aerators work by pumping air to the bottom of the river, where streams of bubbles are injected into the water. As the bubbles rise to the surface, a portion of the oxygen they contain dissolves into the water. Throughout the year, the Port operates the aerators whenever DO concentrations drop below 5.2 mg/L. However, from August to November, that threshold is raised to 6.2 mg/L to benefit the winter-run of the endangered Chinook salmon that pass through on their way to spawn upstream. DO levels in the San Joaquin River are monitored daily by the Port of Stockton Environmental and Regulatory Affairs Department using a monitoring station that is maintained and operated by the California Department of Water Resources. Data are collected from this station every 15 minutes, and monitoring is updated every hour. Current data from the Rough & Ready Island station are available for viewing online at the Department of Water Resources California Data Exchange Center.
Although operation of the existing aerators do not completely eliminate the problem of low DO in the DWSC, it has been demonstrated that they are very effective in raising DO and episodes of critically low DO levels has been all but eliminated.