Home » pH » Page 2

Tag: pH

Out and About with the Casco Baykeeper

Out and About with the Casco Baykeeper

As always, Casco Baykeeper Ivy Frignoca has been on the move, working across Casco Bay, the state—and the nation—on efforts to protect the environmental health of Casco Bay.

A peek into her appointment calendar shows some of the highlights so far this year, as she continued to track Legislative issues and to comment on proposed wastewater and stormwater discharge permits that the Department of Environmental Protection issues to municipalities.


I became coordinator of the Maine Ocean and Coastal Acidification Partnership (MOCA) for 2018.

I will help coordinate research and advocacy on ocean acidification with a strong statewide network of policy makers, fishermen, shellfish growers, and scientists. This year-long role supports our work examining coastal acidification and excess nitrogen.


I invited Portland’s Water Resources Manager, Nancy Gallinaro, and Portland Water District’s Director of Wastewater Services, Scott Firmin, to travel with me to meet the new Environmental Protection Agency (EPA) Region 1 Administrator, Alexandra Dapolito Dunn. We highlighted our joint efforts to reduce nitrogen pollution, combined sewer overflows, and stormwater pollution to Casco Bay. I shared our data showing the impacts of climate change on Casco Bay.

Our Casco Baykeeper meets EPA Administrator Alex Dunn.


Administrator Dunn accepted our invitation to come to Maine in June to attend a meeting of the Maine Nutrient Council, a group convened by Casco Bay Estuary Partnership. Afterward, Administrator Dunn will tour the Bay on our Baykeeper boat, a great opportunity for a close-up view of issues that threaten the water quality of Casco Bay.


Senator Angus King greets fellow Mainers Bill Mook, Hattie Train, Ivy Frignoca, and Richard Nelson.

I traveled to Washington, DC, at the invitation of Ocean Conservancy, to meet with our Congressional delegation and ask for full funding for the National Oceanic and Atmospheric Administration and the EPA. The measures we pressed for passed in the omnibus budget!

Back in Maine, I submitted comments opposing offshore drilling and then attended a meeting hosted by the Bureau of Ocean and Energy Management, to voice Friends of Casco Bay’s opposition to offshore drilling. I supported a resolve that was passed unanimously by our state legislature expressing its opposition to offshore drilling.


I testified at a public hearing as we worked to swiftly defeat a bill that would have practically eliminated the ability of municipalities to pass pesticide ordinances. If you contacted legislators after receiving our email alert about this issue, thank you! The bill was defeated!

I traveled to New Hampshire to attend a meeting of experts concerned about the rise in harmful algal blooms throughout the region, so we could learn more about new species appearing in Casco Bay.


I attended a meeting in West Bath, which drew together people who live and work along the New Meadows River, to discuss how expanding efforts in aquaculture may figure into the many uses of the estuary.

Research Associate Mike Doan gave Kate Simpson and Kayla McMurray, staffers for Senator Susan Collins, a ride to our Continuous Monitoring Station in Yarmouth. I met them at our “Cage of Science” as we demonstrated how we use technology to monitor the Bay hourly, 365 days a year. We explained that though we do not receive funding directly from the EPA, the Agency has a vital role in advising state regulators on strategies to reduce pollution, funding other research, and enforcing the Clean Water Act. This work helps us all protect the environmental health of Casco Bay.


The Portland Water District (PWD) hosted a ribbon-cutting ceremony to celebrate the completion of the massive, $12 million project that upgraded the aeration system at the East End Wastewater Treatment Facility. This improvement could ultimately reduce nitrogen in the treated sewage released into the Bay by up to 1000 lbs. a day! PWD’s General Manager Carrie Lewis recognized our contribution “to understanding the issues affecting Casco Bay and make positive contributions towards collaborative solutions.”

The Maine Ocean and Coastal Acidification Partnership (MOCA) is a volunteer partnership that seeks to coordinate the work of governmental agencies and private organizations and citizens who are studying and implementing means to reduce the impacts of or help adapt to ocean and coastal acidification.

The Maine Ocean and Coastal Acidification Partnership (MOCA) is a volunteer partnership that seeks to coordinate the work of governmental agencies and private organizations and citizens who are studying and implementing means to reduce the impacts of or help adapt to ocean and coastal acidification.

With my colleagues in the MOCA Partnership, I hosted a workshop for nearly 60 scientists, harvesters, policy makers, and advocates on What We Know about Ocean Acidification and Maine’s Lobsters. The event at Bowdoin College featured current research on the effects of climate change on lobsters and emphasized the need for ecosystem-level, long-term studies.

As the year progresses, I look forward to continuing to keep you updated on the biggest issues affecting the health of the waters we all love.

Interactive Casco Bay Health Index

Interactive Health Index

Friends of Casco Bay has developed the Casco Bay Health Index, an easy-to-interpret, visual guide to the health of the Bay. The Index allows us to integrate data from selected water quality parameters into a single value to compare and rank each site as Good, Fair, or Poor.


Now we have our new Interactive Health Index!

By clicking here, or the image below, you can see and interact with the Health Index. The Interactive Health Index will open in a new tab. By clicking on the dots you can see more about each sampling location.

Interactive Casco Bay Health Index

Overall, the water quality in Casco Bay is good, but there are instances when low oxygen, low pH, and murky waters are cause for concern. The 2016 Health Index reveals that over 31% of the sites are considered Poor, but more than 36% of the sites meet the Good standard.

The relative rankings were calculated by analyzing dissolved oxygen, water clarity, and pH data from shoreside sites that our volunteer Citizen Stewards monitored from 2012 to 2016. The values we chose to use were the 90th percentile of the dissolved oxygen percent saturation, the mean of the Secchi depth, and the mean of the diurnal differences in pH.

Commonly Asked Questions about the Casco Bay Health Index


What is the Casco Bay Health Index?

The Casco Bay Health Index was developed to provide a reliable, uncomplicated composite indicator of the Bay’s health, while also illustrating relative levels of eutrophication. The Index allows the scientifically-sound data collected through Friends of Casco Bay’s Water Quality Monitoring Program to be presented in a format that is easy to understand and to update.


What is the goal of the Index?

The goal of the Health Index is to present water quality information in an easy-to-understand visual format by condensing a large amount of existing data into a single score for each monitoring site. By summarizing a suite of environmental parameters into one score for each water quality monitoring site, each site can be ranked relative to one another, and trends—if there are any—can be more readily identified. This product, while quantitative in nature, should be considered a qualitative place to begin to determine environmental health. The sites are assigned colors—red, yellow or green, and are mapped to indicate the health of the waters around Casco Bay. Then we can ask: Which sites, based on the selected criteria, require a closer look? What is the relative condition of sites across a region? Are these conditions improving or degrading over time?


Where do the data for the Health Index come from?

The data used for the Health Index come from Friends of Casco Bay’s Citizen Stewards Water Quality Monitoring Program. Volunteers are well-trained using EPA-approved protocols developed by Friends of Casco Bay. They monitor specific sites and collect the data twice a day on 10 appointed Saturdays, between April and October. The Index incorporates the data for a 10-year span of time and can be updated annually by adding the most recent year’s data and eliminating the oldest. We can also look at the Index in five year increments to compare changes over time.


Which of the existing water quality parameters are most appropriate to use in the Index?

Friends of Casco Bay currently monitors five physical and chemical water quality parameters through our Citizen Stewards Water Quality Monitoring Program: temperature, salinity, dissolved oxygen (DO), Secchi depth, and pH. Of these, three have been selected for use in the Health Index—DO, Secchi depth, and pH.


Dissolved oxygen (DO) DO is expressed as Percent Saturation in order to incorporate temperature and salinity. When water holds all the oxygen it can at a given temperature and salinity, it is said to be 100% saturated. At a given site during a given sampling event, temperature and salinity are measured, and DO is measured in milligrams per liter (mg/l) and then compared with the mg/l for 100% saturation in those conditions. We look at the distribution of the Percent Saturation data; we consider the lowest 10th percentile as the worse-case conditions for a particular site. That 10th percentile threshold, expressed as a Percent Saturation number, becomes a component of the Health Index for that site.


Simply averaging all the DO data for a site might obscure the full extent of any challenged conditions. For example, if a site is eutrophic, wherein nitrogen pollution levels have resulted in a huge algal bloom, there will be large swings in DO levels between the morning and the afternoon; simply looking at the mean would obscure these swings.


Secchi depth Secchi depth is a measure of water clarity. The Index uses a mean of the data to characterize each site. Sites with more organic matter and sediments in the water will be murkier and will exhibit reduced clarity, resulting in shallower (lower) Secchi depth measurements.


pH pH is a measure of the acidity of the water. pH data exhibit tremendous variability—diurnal differences through the day and seasonal shifts through the year. The Water Quality Monitoring Program requires that measurements be collected at 7:00 a.m. and then again at 3:00 p.m. on each monitoring day. This allows for a look at the change in conditions over the course of a day. The pH at a site is influenced heavily by respiration and photosynthesis. Respiration by algae, both seaweeds and phytoplankton, adds carbon dioxide to the water, which lowers pH. Measurements collected in the early morning, at 7:00 a.m., reflect the conditions found after a night of respiration and no photosynthesis. Photosynthesis of course requires sunlight and removes carbon dioxide from the water, raising pH. By afternoon, at 3:00 p.m., pH measurements will reflect the result of photosynthesis. The change between the morning and afternoon measurements, termed the diurnal swing, can be indicative of the magnitude of respiration and photosynthesis, and, indirectly, the amount of algae in the water. Since an excessive bloom of algae is one symptom of nitrogen pollution, a large diurnal swing in pH can serve as an indicator of excess nitrogen. A small change in pH is expected in a healthy, productive coastal system, but a relatively large swing can indicate a challenged site. We calculate the difference between the morning and afternoon readings, the diurnal swing, then amass that dataset to calculate the mean for the Health Index for that site.


What ranges are most appropriate for the component parameters?

For each of the three components of the Health Index, we have defined ranges, between which we would expect to see worse-case and best-case conditions. These ranges have been defined by looking not only at data for Casco Bay, but also data from other regions, state and federal guidelines, and relevant scientific literature.


Parameter: 0 point value 100 point value
Percent Saturation of Dissolved Oxygen 65% 95%
Secchi Depth (meters) 0.2 m 3.0 m
pH (diurnal swing) 0.4 0.1


How is the Health Index score calculated?

Each of the components calculated for a given site is plotted along the scale for that parameter. We use a natural logarithm formula to determine where on the scale of 0 to 100 a particular component falls. For example, a site’s calculated 10th percentile threshold for the Percent Saturation parameter will fall between 65% and 95% at a specific point on the scale between 0 and 100. The same is done for the Secchi depth component and the diurnal swing in pH. Now we have three numbers which fall between 0 and 100. These are added together and divided by 3 to obtain the mean, which is the Health Index score for that site.


How are the final Health Index scores presented?

After each site has a Health Index score associated with it, it can be classified as Good, Fair, and Poor, determined by score thresholds. A score of 85 and above is considered “Good”, a score of 70 to 84 is “Fair”, and anything below 70 falls into the “Poor” category.


What is eutrophication?

Eutrophication occurs when too many nutrients (and occasionally other factors) fuel explosive plant growth. While nitrogen is an essential nutrient in marine systems, too much nitrogen can become a pollutant when it triggers excessive algal growth. This growth can result in low DO measurements, shallow Secchi depth readings, and wide variations in pH.

Seastars on Continuos Monitoring Station

Keeping an eye on the Bay 24/7

Seastars on Continuos Monitoring StationImagine 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 Yarmouth to collect data once an hour, every hour, year round. Appropriately, these high tech tools comprise our new Continuous Monitoring Station. These hard workers have been in place since July 2016.


Why is this hourly data vital?


The steady flow of data our Continuous Monitoring Station collects will help us detect and document how climate change and other emerging coastal stressors may (or may not) be affecting the Bay. Hourly data will help us identify daily, seasonal, and annual trends and better understand the extent to which ocean acidification may be impacting the water chemistry of Casco Bay. The station may also help us assess sea level rise. The station collects data on oxygen levels, carbon dioxide (CO2), pH (the level of acidity of the water), salinity, temperature, chlorophyll, and water depth.


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


Mike hauls up the anchored devices, uploads data from the CO2 sensor to his laptop, and scrapes off marine hitchhikers such as sea stars, tunicates, and algae. “It’s amazing how fast sea creatures occupy any available surface, including our instruments!” says Mike. Before he leaves, he replaces the datasonde with one freshly calibrated and lowers the entire Continuous Monitoring Station back onto the ocean floor. Such attention to detail provides quality assurance that the data is accurate.


While this station is busy year around, we continue to enlist volunteers to help us understand the overall health of our marine waters and to identify troubled areas of the Bay. From April to October each year, more than 90 volunteer Citizen Stewards monitor scores of shoreside sites where they measure five parameters of the surface water: pH, salinity, water temperature, water clarity, and oxygen level. If you are interested in becoming a water quality monitoring volunteer, you can learn more about the program here.


Our volunteers, staff scientists, and now our automated partners, all play a role in helping us to better understand what is going on in Casco Bay.



Thank you to funders of this project, including Casco Bay Estuary Partnership, Davis Conservation Foundation, Horizon Foundation, Schwartz Family Fund of the New Hampshire Charitable Foundation, and WEX. We also thank our Members and the many donors, local businesses, and foundations that give us operational support to do our work each year.



Althea McGirr at LIttle Diamond Island

Althea Bennett McGirr says, “It shucks to be a clam!”

Althea McGirr at LIttle Diamond Island
Althea Bennett McGirr, a Board member since 2011, doesn’t need Friends of Casco Bay to tell her that the chemistry of Casco Bay is changing. She has seen the effects of Coastal Acidification firsthand.

At the annual Labor Day clambake on Little Diamond Island, Althea and her sister Priscilla help out at the end-of-the-season event that draws the community together for a farewell to summer. While the lobsters, sweet potatoes, sausages, and corn are roasting in a fire pit outside the hundred year-old Casino, their job is to wash and de-sand freshly harvested Casco Bay clams.

Althea recalls scooping huge handfuls of clams into 8 heavy kettles to steam them for the feast. Nowadays, they have to place the clams into the pot delicately, or else the shells may end up chipped or even shattered. Althea says that the clams they buy now are smaller and more fragile than the ones she
recalls from years back.

Althea’s observations seem to correspond to observations Friends of Casco Bay has been making over the years. We are studying Coastal Acidification, the problem of increasing acidity from the ocean absorbing carbon dioxide released by the burning of fossil fuels, and, we believe, from excess nitrogen washing into coastal waters by stormwater runoff. Fertilizers, sewage discharges, and pet wastes trigger algae blooms that add excess carbon dioxide to coastal waters.

Pitted Clam
The pitted shell shows that life can be tough for a clam spat in acidic mud.

Our data shows that the acidity of Casco Bay has increased since we began our water quality monitoring program nearly 25 years ago. In 2011, we began sampling the pH (acidity) of mudflat sediments, where soft-shell clams live. We found that the mud nearest to shore was more acidic (had lower pH) than sediments further away from sources of land-based pollution. Higher acidity makes it harder for shellfish to extract calcium carbonate from their environment, the material that clams, mussels, and other mollusks need to build and strengthen their shells.

In the summer of 2014, Friends of Casco Bay installed several clam “condos” in the intertidal mudflats of Recompense Bay in Freeport. Our goal was to see what would happen when we exposed juvenile clams to acidic mud. Research Associate Mike Doan caged baby clams inside PVC tubes and left them in the mud for several days. Microscope photographs of the tiny clam spat showed that after just one week, their shells had become pitted, showing signs of dissolving.

The Double Whammy—Climate Change and Nitrogen Pollution

Photo by Kevin Morris

Nearly everyone has heard of the threat of global warming—as more carbon dioxide is released into the atmosphere through the burning of fossil fuels, the planet’s climate is changing. Not all carbon dioxide released into the atmosphere stays there; scientists estimate that nearly a third is absorbed by the oceans. As marine water absorbs this carbon dioxide, it forms carbonic acid, making the oceans more acidic. Scientists have discovered that over the past two hundred years, the average pH of the ocean has dropped 0.1 pH units. This means that the world’s oceans have become 30% more acidic than they were before the start of the Industrial Revolution. As more and more carbon dioxide is released into the atmosphere, the pH of the oceans continues to decline. This is known as Ocean Acidification.

Casco Bay suffers from a double whammy of carbon dioxide resulting from human activities. First, there are the effects on our local waters from Ocean Acidification. But we are finding excess nitrogen coming from onshore sources, namely polluted rainwater running off fertilized lawns and city streets, emissions from smokestacks and tailpipes, and sewage discharges, all of which send an overdose of nitrogen into our coastal waters. This nitrogen bonanza can stimulate the growth of large blooms of algae, beyond what animals in the ecosystem can consume. Much of these blooms end up dying and settling on the mud. This organic material decomposes; the bacteria responsible for decomposition respire during this process, removing oxygen and adding carbon dioxide. The carbon dioxide and seawater combine to form carbonic acid, lowering the pH of our water and our clam flats. This is called Coastal Acidification.

As more nitrogen pollution enters the Bay, more algae are produced, resulting in more decomposition, which adds more carbon dioxide to the water and sediments, lowering pH. This increased acidity can mean dissolution and death for young clams and other shellfish.


We See a Disturbing Trend in the pH of Bottom Water

At our sentinel sites over the past decade, pH has been trending in the wrong direction.
y = -0.01x + 36.6, R2 = 0.39*
*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.

Measurements at our sentinel sites show a decline in the pH of the bottom water. The points on the graph to the right show annual mean pH for each of thirteen years and illustrate high variability; the dots bounce all over the graph. While this is not surprising, given that coastal systems everywhere exhibit high variability, we did not expect to see this statistically significant downward trend in pH, with the overall slope of the line dropping 0.014 pH units per year over the thirteen-year period. This is a serious and disturbing trend.

Read the next section of the report Nitrogen—Can’t Live Without It, Can’t Live With Too Much of It

The Impact of Coastal Acidification—It Shucks to Be a Clam

In the summer of 2014, Friends of Casco Bay placed hatchery-reared baby clams in the mud at Recompence clam flat in Freeport, Maine, where we measured very low pH levels. Image A shows a clam prior to deployment in the mud. Image B shows a clam after just one week in the mud, where it became heavily pitted due to the high acidity of the mud. Image C is a close-up of the same clam. All of the deployed clams exhibited obvious signs of pitting.

As our coastal waters become more acidic (as the pH decreases), clams, mussels, and other shellfish are having a harder time building and maintaining their shells. Juvenile clams may dissolve outright. Our research has found a disturbing link between acidic mud and clam flats where it is no longer profitable for clammers to harvest shellfish.

In 2011, Friends of Casco Bay began to publicize and investigate coastal acidification. We developed a scientific procedure for sampling the acidity of mud on clam flats. We wanted to compare the pH of clam flats that are actively being harvested by clammers to those that are no longer productive.

This groundbreaking work assesses how acidified sediments threaten the survival of baby clams in Casco Bay. Three years of data show that areas with the highest acidity (lowest pH) are the same flats where clams are now scarce.

We found a strong correlation between high levels of nitrogen and carbon in the mud—indicating organic matter— and lower pH. In other words, a lot of dead, decaying stuff makes matters worse.

Many people are interested in the results of our cutting- edge coastal acidification research, including the 1,700 registered Maine diggers who support a $16.8 million-a-year industry harvesting soft-shell clams. Those of us who define summer as a delicious plate of steamers have a gastronomic interest, too!

Our research on mud pH on 30 clam flats around Casco Bay suggests that the more acidic the clam flat, the less hospitable it is for clams.

Read the next section of the report Lawns Are to Blame for Much of the Nitrogen and Toxic Chemicals in the Bay

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