By Joy Hampton
The Norman Transcript
NORMAN — An experimental prototype at Lake Thunderbird is making history and could provide solutions for troubled lakes everywhere.
Now in its third year, the Supersaturated Dissolved Oxygen System, or SDOX, is showing positive results.
Steven Cadenhead from the Oklahoma Water Resources Board reported the program’s success to the Central Oklahoma Master Conservancy District board on Thursday. The primary goal of the experimental project is to add oxygen to the bottom layer of lake water.
“We’re able to make a noticeable effect in a good chunk of the target area,” Cadenhead said. “There was a really good dispersal of oxygen in the target area.”
Organic matter and nutrients like phosphorous build up in the bottom of lakes. The organic matter uses oxygen as part of the decomposition process.
During the winter, the lake water is the same temperature, but as the upper portion of the lake water warms in the spring, the lake stratifies, isolating the bottom of the lake.
That isolation lets the decomposition of organics pull the oxygen from the lower depths. The lack of oxygen causes nutrients such as phosphorous to release from the sediment at the bottom of the lake.
In the fall as the water cools, that nutrient-rich, isolated water rises and feeds the algae. In addition to other problems, this algae is one of the primary contributors to taste and odor problems in Norman’s drinking water from the lake.
While recent TMDL studies by the Department of Environmental Quality map the amounts of nutrients like phosphorous that are feeding into the Lake Thunderbird watershed, COMCD did not wait for that study to take proactive action to improve water quality.
By working with BlueInGreen out of the University of Arkansas to install the SDOX system, the board hoped to improve the water quality of its municipal customers.
The start-up costs of the project were funded through the American Recovery and Reinvestment Act channeled through OWRB. COMCD pays for the oxygen and does maintenance on the system.
At this time, there is one treatment area by the dam, where the lake is deepest. By treating this problem area, the whole lake benefits, but this area is key because it’s also the location of the raw water intake for the lake’s municipal customers.
An original goal of the SDOX system was to increase dissolved oxygen in the lower strata of the lake without mixing upward. If mixing occurs, some of the oxygen is lost upward, instead of staying in the lower lake level where it’s needed most.
A secondary goal is to reduce the sediment phosphorous to prevent algae bloom and to reduce the total organic carbon in the lake.
A long-term goal is to lower drinking water costs and reduce taste and odor complaints by water consumers.
During the first two years, the program showed some success, but mixing of the layers occurred. However, the lake’s oxygen increased and broke the trend of rising levels of chlorophyll-a. Monitoring chlorophyll levels is a way to track algal growth.
BlueInGreen made some adjustments and solved the mixing problem. Even though the SDOX system was off during a portion of July for repairs, once it was operational, the improved oxygen levels quickly returned.
“It’s going to take us a while to lower that sediment oxygen demand,” Cadenhead said.
Compared to 2007, which was a similar year with a lot of inflow from rain, calculations showed the difference in oxygen levels this year as strongly improved.
The areas of anoxia (lack of oxygen) in the deep parts of the lake were the lowest ever calculated by OWRB.
The system pulls water from the depths, infuses it with oxygen and puts the water back at the same temperature so it stays at the same low level where the oxygen is needed. Because the oxygen is dissolved, saturating the water, it stays in place.
The SDOX prototype is the only system of its kind, but BlueInGreen will likely build on the success at Lake Thunderbird to set up other pilot projects, Cadenhead said.