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Category: Seasonal Sampling

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.

What did we see on the Bay this summer?

Last week over 165 Friends of the Bay joined Casco Baykeeper Ivy Frignoca and Staff Scientist Mike Doan online at our latest Casco Bay Matters Event: What Casco Bay Is Telling Us.

Here is a recording of the event for those of you who were unable to attend or would like to revisit the conversation.

Every year, Ivy and Mike traverse the Bay by land and boat from May through October, collecting water quality samples and speaking with those who live, work, and play on the water. At last week’s Casco Bay Matters event, Ivy and Mike shared their observations from this past field season, what our data are telling us about the health of the Bay, and what we all need to do moving forward to keep Casco Bay blue.

If you don’t have time to watch the whole recording, here are a few clips of key moments you may find interesting:

CLIP #1: In this 90-second clip, Staff Scientist Mike Doan breaks down what he sees in the salinity data (the saltiness of seawater) from our Continuous Monitoring Station in Yarmouth. This year the Bay was particularly salty and Mike has thoughts as to why.

CLIP #2: What does the construction project surrounding Portland’s Back Cove have to do with the health of Casco BayIn this 2 minute clip, Casco Baykeeper Ivy Frignoca explains how the big construction project that you can see from I295 reduces pollution while accounting for the impacts of climate change.

CLIP #3: In this 90-second clip, Casco Baykeeper Ivy Frignoca explains how Volunteer Water Reporters are informing our advocacy and helping us track changing conditions seen on Casco Bay.

Want to watch the full 60-minute eventHere it is!

Data from our seasonal sampling program and our three Continuous Monitoring Stations can be viewed at cascobay.org/our-work/science/.

A View from the Hill: The Bay Rests

Friends of Casco Bay Board President Sandy Marsters recently wrote an ode to the Bay in fall, for his regular column with the Portland Phoenix. “There is calm as the Bay breathes with the tides,” writes Sandy, “great inhales and exhales that roll the stones round onshore, polish the sea glass, break in long whispers along the sand.” You can read Sandy’s full column about the beauty of the Bay in autumn, here.

You’re invited: What Casco Bay is Telling Us

Casco Baykeeper boat on the water at dawn

Casco Bay is changing and changing quickly. Join Casco Baykeeper Ivy Frignoca and Staff Scientist Mike Doan for a conversation about what Casco Bay is telling us and what we, as a community, need to do moving forward. On Wednesday, October 27, grab your lunch, log on to Zoom, and join the conversation. Ivy and Mike will be sharing with us their observations and experiences from this field season, what our data are telling us, and how you can help as we work to improve and protect the health of Casco Bay.

You must register to join this event. We would love for you to join us.

Register

What: What Casco Bay Is Telling Us: A Casco Bay Matters Event

When: Wednesday, October 27, Noon to 1 p.m. 

This event will take place via Zoom. We will send you instructions for joining the event after you register.