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Decades of Data: A Watershed Year for Science

This year we are marking two important milestones: our 30th season of monitoring the water quality of Casco Bay and the first full-year of having three Continuous Monitoring Stations in the water.

Staff Scientist Mike Doan says that both our Seasonal Sampling and Continuous Monitoring efforts are crucial to our mission to protect the health of the Bay. “Casco Bay covers more than 200 square miles of water,” he explains. “Our monitoring programs are designed to efficiently measure how healthy various parts of the Bay are while tracking how our waters are changing over time.”

“We are proud to say that we have stuck with science for the long-haul,” says Will Everitt, Executive Director of Friends of Casco Bay. “It takes tenacity to stick with any long-term project. It takes committed supporters and donors to ensure that we have the resources to continue this work year in and year out. If you are one of those supporters, thank you. You’ve helped us reach these milestones.”

The Casco Bay Estuary Partnership (CBEP), one of 28 federal National Estuary Programs, is among the many entities that put our data to use. “For three decades, Friends of Casco Bay’s monitoring efforts have provided a crucial part of the data used to understand the condition of Casco Bay,” says Curtis Bohlen, Director of CBEP. “The data are relied on by scientists and regulators alike. Friends’ thirty year history of monitoring the Bay provides a long term perspective crucial for understanding how the Bay is — and is not — changing.”

30 Years of Seasonal Sampling

Our Seasonal Sampling program continues to add to one of the most-important and long-term marine water quality data sets in New England. Data from this program helped to designate Casco Bay as a Federal No Discharge Area and upgrade Clean Water Act classifications for large areas of the Bay, ensuring our waters are better protected for years to come.

From May to October, Staff Scientist Mike Doan and Casco Baykeeper Ivy Frignoca take to our Baykeeper boat or truck and travel to 22 sites across the Bay.

“We are providing a health check-up for the Bay each day we are out there,” Mike explains. “Like a doctor checking your blood pressure, if we find an anomaly or problem, we can do more thorough investigations.”

365 Days of Continuous Data

Mike and Ivy use a scientific device that measures water quality characteristics called a data sonde to measure temperature, dissolved oxygen, pH, salinity, chlorophyll, turbidity, and water depth. They also collect water samples that we send to a laboratory to measure total nitrogen.

As of May 20, 2022, Friends has a full year of around-the-clock data from all three of our Continuous Monitoring Stations. In May 2021, we launched two new Continuous Monitoring Stations in Casco Bay, located off Harpswell to the east and in Portland Harbor to the west. These two Stations joined our original station off the coast of Yarmouth, near the coastal center of the Bay, first launched in 2016.

Mike designed our Continuous Monitoring Stations, which combine a data sonde with a sensor that collects carbon dioxide data. “We launched the stations to measure how the Bay is changing,” says Mike. “By looking at data collected every hour on the hour, we can better see through the noise of daily and seasonal changes, and understand how climate change may be impacting our waters. Having three stations up and running for more than a year now is giving us a clearer picture of what is happening in very different regions of the Bay.”

Our Continuous Monitoring Stations are maintained thanks to the generous support of the Casco Bay Estuary Partnership and the more than 700 Friends of the Bay who gave to our Climate Change and Casco Bay Fund.

Bay temperatures rise as oxygen levels dip

Friends of Casco Bay has been collecting water quality data on the health of the Bay for 29 years. A recent analysis of our seasonal long term dataset shows that water temperatures are on the rise in Casco Bay.

 

On average, water temperatures in Casco Bay are increasing at an approximate rate of 1°F every decade.*

“It’s alarming to see we’re going in the wrong direction,” said Staff Scientist Mike Doan. “There are so many ways that warmer water can impact the Bay. A primary concern is that warm water species are moving in and cold water species are moving out. Invasive green crabs, for example, thrive when the Bay is warmer. On top of species shifting, we are also looking at a system that is increasingly susceptible to nitrogen pollution. And that’s only the tip of the iceberg.”

When Mike says warmer waters make the Bay more susceptible to nitrogen pollution, he is thinking about how excess nitrogen can lead to lower levels of oxygen in the water. Nitrogen pollution comes from sources such as stormwater and wastewater treatment facilities. When excess nitrogen enters the Bay, it can spur the rapid growth of plant life and algae. When these plants inevitably decompose, they can consume so much of the oxygen in the water that aquatic animals like fish and shellfish struggle to breathe, and can even die.

On the whole, Casco Bay contains healthy levels of oxygen. However, water temperature and oxygen have an inverse relationship. Warm water holds less oxygen than cold water, and as water temperatures in the Bay rise, Mike has observed a corresponding decline in dissolved oxygen (a measure of how much oxygen is in the Bay).

 

On average, levels of dissolved oxygen are healthy in Casco Bay but are slowly decreasing at an approximate rate of 0.1 mg/L every decade.*

“There’s a very healthy amount of oxygen in the Bay right now, and the decline we’re observing is moving at a slow pace,” said Mike. “However, it’s important to keep our eye on this trend. As climate change causes the Bay to warm, oxygen levels will continue to decrease. With it, the impacts of nitrogen pollution and associated drops in oxygen will grow.”

Scientists up and down the New England coastline are reporting similar trends in temperature and dissolved oxygen. At Friends of Casco Bay, these trends are based on Mike’s analysis of a subset of 29 years of our seasonal sampling data. Specifically, Mike looked at data from three locations in the Bay that we access by boat near Fort Gorges, Clapboard Island, and in Broad Sound. At each of these sites we collect data at the water’s surface, and then every two meters down to the bottom of the Bay, to create a “profile” of the water column. Every one of these data points is included in Mike’s analysis, making him confident that these trends accurately reflect changing conditions in Casco Bay.

 

* The exact rates: water temperatures are rising at 0.99°F per decade and dissolved oxygen levels are decreasing at 0.091mg/L per decade.