Northern Georgia will soon have a new freshwater reservoir: Lake McIntosh. The proposed 650-acre lake will sit on the border of Fayette County and neighboring Coweta County, eventually providing more than 10 million gallons of drinking water per day.
But first, the Fayette County Water System must assure the United States Fish and Wildlife Service (USFWS) that endangered mussels living in the targeted creek will be safe.
To verify this, Atlanta-based CCR Environmental is conducting physical and biological analyses of Line Creek, downstream of the proposed reservoir. Part of this work will involve measuring dissolved oxygen levels, which is being done with a HOBO U26 Dissolved Oxygen data logger from Massachusetts-based Onset Computer Corporation.
The amount of dissolved oxygen in a body of water is an indicator of its health: high dissolved oxygen correlates with high biological productivity, and low dissolved oxygen means lower biological productivity. Because all animals, including mussels, require oxygen for respiration, dissolved oxygen is an important indicator of the relative health of an aquatic animal’s environment.
Under the Endangered Species Act, the USFWS requires consultation for any project that may affect federally-protected species or their critical habitat. The Lake McIntosh project was determined to potentially impact several federally-protected mussel species, including the oval pigtoe (Pleurobema pyriforme), shinyrayed pocketbook (Hamiota subangulata) and Gulf moccasinshell (Medionidus penicillatus).
According to CCR Aquatic Ecologist Chris Crow, the team previously measured dissolved oxygen in the field with hand-held probes. “Our option was to do it manually,” Crow explained, “meaning that once a week we had to go out to the site before dawn with a meter.” It is general practice to measure dissolved oxygen just before dawn, when levels are at their lowest.
The Onset dissolved oxygen logger is self-contained, and can be deployed and left to take measurements in a body of water, either fresh or saltwater, for weeks at a time. It records dissolved oxygen levels as often as the user chooses, and the data is time-stamped and downloadable to a laptop computer or a hand-held data shuttle device offered by Onset.
The logger was deployed in sandy-bottomed Line Creek with the help of a six-foot metal fence post. It was attached to the post with zip ties, and fit vertically into the U-shaped groove in the post.
“It’s important that the logger be placed in the deep part of the stream in a well-mixed area, with the sensor down low enough so it’s not going to expose the probe if the water level drops,” said Crow.
As expected, the collected data has shown that dissolved oxygen levels were lowest in midsummer, when the creek’s flow is lowest and temperature is highest.
“We can see the highs and lows, and can see the diurnal [day/night] cycle now, too,” said Crow. “It’s reassuring to confirm it’s there.”
The data will provide the dissolved oxygen information required by the Fish and Wildlife Service, and will help determine how reduced stream flow will affect dissolved oxygen – and by extension – the organisms in the stream. The data will also serve as baseline data for habitat comparison post-construction of the Lake McIntosh dam.