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Continuous Monitoring Station

Imagine working 24 hours a day, 365 days a year.

Friends of Casco Bay has two water quality monitors that do just that: a data sonde, an instrument that can measure several properties of water at once, and a separate device that measures carbon dioxide. They are anchored together in a re-purposed lobster trap on the ocean floor. The monitors collect data once an hour, every hour, year round. Appropriately, these hard-working, high-tech tools comprise our new Continuous Monitoring Station

Understanding a Changing Casco Bay

The steady flow of data that our Continuous Monitoring Station collects helps us detect and document how climate change and other emerging coastal stressors may (or may not) be affecting the Bay. Hourly data helps us identify daily, seasonal, and annual trends and better assess the extent to which ocean acidification may be impacting the water chemistry of Casco Bay.

By deploying a data sonde and a carbon dioxide sensor, we are able to collect hourly data on temperature, salinity, dissolved oxygen, pH, chlorophyll fluorescence, and carbon dioxide. These measurements can also be used to calculate additional parameters. By adding these additional parameters, we get a more complete picture of acidification in the Bay. Friends of Casco Bay also uses the Station to track invasive species.

This electronic station, located off Yarmouth near the center of the Bay, was launched in 2016 and is vital to monitoring the long-term health of our waters.

What We Are Learning

Research Associate Mike Doan has nicknamed the Continuous Monitoring Station our “cage of science.” Having more data on carbon dioxide, which has an impact on the acidity of our coastal waters, will aid not only our advocacy and education efforts, but also inform the work of other scientists, government officials, and activists working to protect Casco Bay.

Highlights from the first year of Continuous Monitoring Station

  • Lowest water temperatures usually occur in January; this year we hit 0oC in December.
  • Salinity in Casco Bay estuary is consistently around 30 parts per thousand (ppt). We did see not a lot of variability; spring snowmelt drops salinity to 25.
  • Dissolved oxygen (DO) is a solid indicator of nutrient pollution. We averaged 8 mg/L; higher concentration in winter; lower in summer; also saw the influence of spring phytoplankton blooms, which add oxygen to the water. Later in summer, there was decomposition of phytoplankton and algae, which pulls oxygen out of the water.
  • Chlorophyll fluorescence readings followed the text book consistency, with levels of healthy 3,4, or 5 micrograms per liter. We see evidence of spring blooms, which our monthly profile trips were not always able to capture consistently. Last year, abundant phytoplankton in summer resulted in a prolonged bloom through the summer, fall, and even into winter.
  • pH has been our primary measure of acidity before we had the pCO2 sensor; it follows the same trend as DO: higher in winter; drops off in summer driven by phytoplankton production. Photosynthesis adds oxygen and raises the pH; when there is more respiration adds more carbon dioxide to water in fall, pH falls.
  • PCO2 sensor: We were surprised at how low the values were: peaked in summer, drop off in winter. Mike noted that we will have a small gap in our data stream, as we have to send it to California for is annual recalibration.

    This is alarming: We need to know the calcium carbonate saturation state (Omega aragonite) in order to understand Coastal Acidification. Aragonite is what clams and other shellfish build their shells out of represents the Calcium carbonate saturation state. A level of calcium carbonate saturation state of 1.5 and above is critical for shell building. Below that, clams—particularly baby clams—cannot grow their shells; juvenile clam shells may dissolve back into the water. Most of the winter readings were below that level. Results were lower than what Mike would have expected. Colleagues are seeing the same thing.

Before our CMS, pH was our acidity indicator. Now that we have a pCO2 sensor, we can use aragonite and other parameters to assess coastal acidification.

More from our Continuous Monitoring Station

Spring starts early in Casco Bay!

February 15, 2018

  It may be hard to believe if you have spent any time outside this chilly winter, but spring likely has sprung in the waters of Casco Bay. By January, the lengthening daylight has jumpstarted the growth of phytoplankton, the single-celled plants that are the foundation of the ocean food… Read more

Continuous Monitoring Station

Monitoring a Changing Casco Bay 365 Days a Year

October 12, 2017

Covered with sea squirts, sea stars, and other marine hitchhikers, the newest member of our monitoring team looks like an abandoned lobster trap. It may be homely, but we are pretty impressed with what it does, collecting water quality data hourly, 24 hours a day, 365 days a year. It… Read more

Seastars on Continuos Monitoring Station

Keeping an eye on the Bay 24/7

January 20, 2017

Imagine working 8,760 hours a year. Friends of Casco Bay has two water quality monitors that do just that: a datasonde, an instrument that can measure several properties of water at once, and a specialized device that only measures carbon dioxide. They are anchored together on the ocean floor in… Read more

The Care and Maintenance of Our Submerged Monitors

Research Associate Mike Doan prepares our Continuous Monitoring Station for cleaning and re-calibration.

In order to ensure continuous data, we have multiple data sondes, which are swapped and refreshed every two weeks. When he arrives at the dock, Research Associate Mike Doan has less than an hour to reposition the alternate data sonde so that we don’t miss any of those 8,760 hours of information.

Mike hauls up the anchored devices, uploads data from the carbon dioxin sensor to his laptop, and scrapes off marine hitchhikers such as sea stars, tunicates, and algae. As he cleans sea life from the Station, Mike records any invasive species attached to our equipment. “It’s amazing how fast sea creatures occupy any available surface, including our instruments!” says Mike.

Before he leaves, he replaces the data sonde with the freshly calibrated one and lowers the entire Continuous Monitoring Station back onto the ocean floor. Such attention to detail provides quality assurance that the data is accurate.

We thank Casco Bay Estuary Partnership and our generous members for helping fund our Continuous Monitoring Station’s first year.