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- The Forecaster
YARMOUTH — About once a month for the past 25 years, Friends of Casco Bay staff have been visiting 10 sites around the bay by boat to collect water quality data.
The significant changes in Casco Bay have caused increasing concern over the last decade, particularly warmer water temperatures later into September over the past five or six years.
But monthly data collection wasn’t enough to gain an understanding of when and why these changes were occurring.
Enter the “Cage of Science,” a lobster-trap-like, first-of-its-kind contraption designed by research associate Michael Doan that was launched off Cousin’s Island in August 2016.
“To really document how things are changing, we needed … high-frequency data collection,” Doan said: a stationary device that could continuously measure water quality autonomously, rather than manually.
“We needed a place to house our (datasonde and partial-pressure carbon dioxide sensor),” Doan said. The datasonde is a multi-parameter monitoring instrument that monitors and records water temperature, salinity, dissolved oxygen, acidity, and depth, while the partial-pressure sensor adds a measurement of the water’s carbon dioxide levels.
The cage takes hourly measurements of each water-quality parameter, which are logged every two weeks when staff visit the site to replace the datasonde and prevent organism growth on the sensors.
The partial pressure carbon dioxide sensor is used to determine if there is an issue with acidity in the bay. Too much carbon dioxide absorbed from the atmosphere results in increased temperatures and acidity; nutrient pollution from run-off can also drive an increase in acidity closer to the bay’s shore.
Four basic measurements can determine water acidity: pH, carbon dioxide, dissolved inorganic carbon, and total alkalinity.
“If you can measure any two of those, you can calculate the other two,” Doan said. “Just by adding that carbon dioxide sensor, we now have all four full (carbon dioxide) parameters.”
With these hourly measurements, he said, Friends of Casco Bay has seen temperature and acidity changes in the water over as little 24 hours.
One of the major concerns with increases in ocean acidity is the effect it has on aquaculture. Doan said if water is too acidic, shellfish will have a harder time building their shells, which are made of calcium carbonate.
Doan said that they’ll need to monitor the cage for much longer than a year to really grasp a baseline for each measurement and see how water temperature and acidity are changing.
He said Friends of Casco Bay’s hope is to eventually add at least one more Cage of Science farther out in the bay.
“What we’re learned is every part of the bay is different, but they seem to be changing at the same rate,” Doan said. “We’re just really trying to track a baseline to see what the conditions are now. Year one is just the beginning of hopefully a very long-term data set.”
Michael Doan in Yarmouth with the “Cage of Science,” a device he designed for Friends of Casco Bay to take hourly measurements of water quality parameters such as temperature, salinity and acidity.