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Category: Monitoring From the Baykeeper Boat

Science: We help you see what is going on beneath the surface of the Bay

Before we started monitoring the water quality of Casco Bay, no one knew how healthy or polluted the Bay actually was. Thanks to the data we have been collecting at dozens of shoreside and offshore sites, we can state that the water temperature of Casco Bay has risen by 2.5°F, on average, since 1993.

Our long-term data set is enhanced by our Continuous Monitoring Station that has been monitoring the health of the Bay hourly, 365 days a year, since 2016. Anchored below a pier in Yarmouth, it provides the frequent, high-volume stream of data necessary to accurately track changes that may impact the oysters, clams, lobsters, and eelgrass within the Bay.

“Climate change is happening so rapidly, we needed to add to the way we collect data,” observed Research Associate Mike Doan. Since July 20, 2016, our Continuous Monitoring Station has been gathering data around the clock, all year long. Each month, we post information on 10 measures that document water quality at our monitoring site in Yarmouth, near the coastal midpoint of Casco Bay. 

Our Monitoring Station is fondly nicknamed the “Cage of Science” because its high-tech sensors are housed inside a converted lobster trap. These instruments measure temperature, salinity, oxygen, pH, carbon dioxide, and more.

These data help us gain new insights—and new questions–on the health of the Bay. Others are finding these data useful, too. Scientists use our data to inform their own research. Policy makers refer to our data to support legislative action on climate change. Classroom teachers have their students analyze our data to launch discussions on what humans can do to improve water quality. Recently, we discovered that young visitors to the Children’s Museum & Theatre of Maine measure the temperature and salinity of the Museum’s touch tank and compare their readings to our real-world data on Casco Bay.

We have posted our data online for all to see. Visit cascobay.org to see for yourself how Casco Bay is changing month by month.

The news media have recently reported on our plan to expand our array of Continuous Monitoring Stations to get a better understanding of the dynamics of Casco Bay:

What’s green, microscopic, and makes ½ our oxygen?

July 1, 2020

What’s green, microscopic, and makes half of the oxygen we breathe? Phytoplankton, the tiny algae at the base of the food chain, that’s what! Measurements of chlorophyll — the green pigment that enables plants and algae to photosynthesize — provide an estimate of how much phytoplankton are in our coastal… Read more

30 years of success protecting the Bay

June 25, 2020

We were delighted to have more than 80 Friends of the Bay join us for our 30th Anniversary Members Annual Meeting on June 16. As Executive Director Cathy Ramsdell said during the event, we only wish we could have held it in person. If you missed the event — or… Read more

A Warm Winter and Spring

June 10, 2020

How warm was winter and spring on Casco Bay? Staff Scientist Mike Doan takes a look at our data. You can always see our Continuous Monitoring Station data here. Read more

Take a tour of our Cage of Science

May 14, 2020

What is this Cage of Science that Friends of Casco Bay keeps talking about? We invite you to join Staff Scientist Mike Doan out on Casco Bay for a short tour of our Continuous Monitoring Station. In this 2 ½ minute video, Mike shows off the high-tech components of the… Read more

Boom and Bust: How phytoplankton influence pH

April 9, 2020

When we look at our water quality data, we can see that some characteristics of the Bay influence other characteristics. In this example, large phytoplankton blooms have a big impact on the chemistry of Casco Bay. Ready for some Marine Science 101? In the graph below, we compare two types… Read more

We’re still monitoring the health of Casco Bay, and you can too

March 25, 2020

It is lonely out on the pier where Staff Scientist Mike Doan is collecting data on the health of Casco Bay — and he is playing it safe, taking his own selfie as seen here. We are continuing to monitor the health of Casco Bay. Our Continuous Monitoring Station is still… Read more

And how is your summer going?

Summer is going swimmingly here at Friends of Casco Bay, and we have a lot of good news to share:

  • Our priority legislative bill to create a state-level Climate Change and Ocean Acidification Council was incorporated nearly word-for-word into the Governor’s comprehensive Climate Change Council bill. An Act to Promote Clean Energy Jobs and to Establish the Maine Climate Council passed with strong bipartisan support. In recognition of her yeoman’s work on this issue, Casco Baykeeper Ivy Frignoca was invited to attend the bill signing by Governor Janet Mills on June 26th.


  • Our water quality sampling season is well underway, as we continue to add to our long-term dataset at 22 shoreside and deepwater sites around the Bay. You may see Research Associate Mike Doan and Casco Baykeeper Ivy making the rounds by land and by sea every few weeks from April through October.


  • Photo by Kevin Morris

    Since early June, Executive Director Cathy Ramsdell has been attending bi-weekly meetings of the South Portland Fertilizer Working Group to assist the City in drafting a fertilizer ordinance.


  • July 20 marks the third anniversary of the launch of our Continuous Monitoring Station in Yarmouth. Our Monitoring Station is fondly nicknamed the “Cage of Science” because its high-tech sensors are housed inside a transformed lobster trap. The instruments measure temperature, salinity, oxygen, pH, and carbon dioxide.
    Photo by Kevin Morris

    Together, they collect data once an hour, every hour, year round.  At this time of year, Mike has to scrape off a new array of marine hitchhikers whenever he hauls up the Cage of Science to download data.


  • ‘Tis the season to think about what not to put on your lawn! With five workshops behind her, Associate Director Mary Cerullo has scheduled another five BayScaping presentations for August and beyond. She is happy to talk with neighborhood groups about green yards and a blue Bay.


  • There has been such a demand by community groups to volunteer for coastal cleanups and storm drain stenciling projects that Community Engagement Coordinator Sarah Lyman and summer intern Alexis Burns have been very busy. They already have hosted seven events with 106 participants who collected an estimated 238 lbs. of trash and stenciled 238 storm drains!


  • Photo by Kevin Morris

    Our new pumpout boat, Headmaster, was launched on June 10th to pump raw sewage from the marine toilets of recreational boats. Captain Jim Splude, our congenial pumpout boat coordinator, can go about his business more efficiently now with a new boat that has more than twice the holding capacity of the old one.


  • Our Water Reporter volunteer project is expanding as we hoped and planned. Nearly 40 enthusiastic volunteers attended our Water Reporter training on June 24. Volunteers continue to sign up to keep watch over specific areas of the Bay.
    July 10 was the first anniversary of Friends of Casco Bay’s launch of the Water Reporter app. To date, 162 volunteers in this observing network have made more than 500 posts. We call that a great start!

Maine Coastal Observing Alliance releases new report

The Maine Coastal Observing Alliance (MCOA) announced the release of its new report on the region’s coastal water quality. MCOA was formed in December 2014 to coordinate a regional effort to monitor coastal waters, particularly estuaries, and detect trends such as those related to ocean acidification and nutrient loading. You can read the report here: http://www.damariscottariver.org/wp-content/uploads/2015/11/MCOA-report-Final-small-vers.-17nov15-2.pdf

Trends in Water Quality

Data collected over the past decade by Friends of Casco Bay has revealed a significant downward trend in pH in bottom water samples at our sentinel sites, as well as a marked difference in nitrogen concentrations between nearshore and offshore sites.

What’s a Sentinel Site?

Friends of Casco Bay’s staff scientists collect water quality data from the surface to the bottom year round at ten profile sites across Casco Bay. In some months, especially during the winter, bad weather prevents us from getting to all ten sites. Even so, as stalwart mariners, we have managed to visit three of the ten sites every month of the year for over 23 years. We call these sites our sentinel sites. We chose to analyze data from the bottom depths of these three sites, where conditions are less affected by wind, waves, and weather:

  • Broad Sound, our deepwater site
  • Clapboard Island, Falmouth, our “suburban” site
  • Fort Gorges, our “urban” site in Portland Harbor


pH Is an Important Factor

pH is a measure of the acidity or alkalinity of water. The pH scale is logarithmic, ranging from 0 to 14. Each whole pH value below 7 (neutral) is ten times more acidic than the next higher value. Though seawater at 8.2 is basic, the ocean’s chemistry is shifting toward the acidic side of the pH scale.

In coastal systems, many factors contribute to variations in pH. The major driver of pH change in seawater is the addition or removal of carbon dioxide. Carbon dioxide and water react to form carbonic acid. The more carbon dioxide, the more acidic the water (and the lower the pH), while the removal of carbon dioxide reduces acidity (and pH is higher). Carbon dioxide is added and removed from seawater in a number of ways, some of which are naturally occurring and some of which are exacerbated by human activity.


Dissolved Oxygen

Photo from the Times Record

Oxygen is essential to marine life. Friends of Casco Bay staff and volunteers test for dissolved oxygen, a measure of how much oxygen is available to marine life. Generally, dissolved oxygen values in Casco Bay are good. But not all areas of the Bay have healthy oxygen levels all the time. The lowest oxygen levels can be found during the early morning in the late summer at river mouths and narrow embayments. In these locations, Friends of Casco Bay has detected oxygen levels that would cause fish, lobsters, and other marine life to be stressed or killed. Low levels of dissolved oxygen in the water contributed to massive die-offs of pogies in the upper New Meadows River and Quahog Bay in the early 1990s. Long-time residents of eastern Casco Bay still remember the awful smell of rotting fish from those die-offs.


The pH of Water in Casco Bay Varies Between Night and Day

Algae can have a huge influence on pH levels in the water. On a daily basis, seaweed and phytoplankton photosynthesize, taking up carbon dioxide and releasing oxygen; this process causes pH to rise throughout the day. But at night, during respiration, algae take up oxygen and release carbon dioxide into the seawater, which lowers pH. These two processes generally result in lower pH in the morning, after a night of respiration, and steadily higher pH by late afternoon. Much of the variability of pH in Casco Bay can be explained by changes caused by photosynthesis during the day and respiration at night. Since oxygen is produced through photosynthesis and removed by respiration, we can see the dynamic in our data when we compare levels of dissolved oxygen in the water to pH: the higher the oxygen levels, the higher the pH; the lower the oxygen levels, the lower the pH. This data is available because of the efforts of our intrepid water quality volunteers, who sample both at 7 a.m. and then again at 3 p.m. on scheduled monitoring days.

The swing in pH from morning to afternoon—the diurnal difference—can be an indication of productivity. The more algae in the water, the greater the diurnal change. A healthy and productive water body will have a relatively modest change in pH from morning to afternoon, but a large swing in pH may indicate that a site is overly productive, or eutrophic. This happens when excess nitrogen over-stimulates algal growth.


The pH of Water in Casco Bay Varies Seasonally

The mean pH values in Casco Bay decline monthly between April and October. This reflects the shifting balance between algal productivity and respiration.

Seasonally, mean pH on a monthly basis drops over the course of the summer. Two dynamics are in play. As waters warm during the summer, mean pH values decline. In addition, algae blooms peak in the spring, then die and decompose through the summer into early fall. Bacteria responsible for decomposition respire and add carbon dioxide to the water and sediments. The overall effect is gradually declining pH values as we head into fall.


Our Staff Is on the Bay Year Round

Friends of Casco Bay staff scientists use our Baykeeper boat to sample our research sites monthly, all year long. By January, our vessel is usually the only boat left in the slips at Breakwater Marina, South Portland. Bundled up in work suits lined with flotation gear, Citizen Stewards Coordinator Peter Milholland and Research Associate Mike Doan shovel snow off the deck and leave early to complete the 75 nautical-mile circuit of the Bay by nightfall. Many winter mornings the air is colder than the ocean, creating a bank of sea smoke that wraps around the islands. The only other vessels encountered are commuter ferries, Coast Guard boats, and oil tankers, their bows caked with frozen sea spray. Our boat stops at each sampling station for about 20 minutes, long enough for hands to become numb. “It’s important to sample all year round in order to understand the overall health of Casco Bay,” explains Peter. By the time the crew returns to Breakwater Marina, the last rays of the setting sun momentarily blind them, a final reminder that nothing is easy on the water in winter. Yet, these stewards agree that being on Casco Bay at this time of year is magical.


Big Daily Swings in pH Can Spell Trouble

In coastal environments—like Casco Bay—there is a close link between pH and dissolved oxygen as algae add and remove oxygen from our marine waters through photosynthesis, respiration, and decay.
y = 32.1x – 151.1, R2 = 0.23*
*The trend lines of the graphs throughout this report illustrate the pattern of the data. The equation (y=) describes the trend line that best fits the data. The R2 value tells us how well the data fit around the trend line, indicating the reliability of the line.

While we expect pH to be variable, large changes in pH over the course of a day can be cause for concern. The average diurnal difference of pH in Casco Bay is about 0.1 pH units. However, some of our monitoring sites experience an average diurnal difference of as much as 0.3 units—this is a huge swing. This indicates that parts of the Bay could be eutrophic, meaning those regions will suffer from lower oxygen levels, increased carbon dioxide levels, increased acidity levels, nuisance algae outbreaks, and potential fish and shellfish die-offs.

Read the next section of the report The Double Whammy—Climate Change and Nitrogen Pollution