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Spring Blooms in Casco Bay

What signs tell you that spring has arrived? Grass turning green? A robin in your yard? Ospreys returning to their nests?

What about huge blooms of phytoplankton in Casco Bay?

The chlorophyll fluorescence measurements in the graph above were recorded by our Continuous Monitoring Station, which has been in place for almost two years.

Chlorophyll fluorescence is a measure that provides an estimate of phytoplankton abundance. Chlorophyll is the green pigment in plants that traps the energy of the sun for photosynthesis.

The graph tells us that this year’s spring bloom of phytoplankton started around the same time as last year, but was bigger in magnitude this year than in 2017.

Why do we care about chlorophyll levels? Phytoplankton are the single-celled plants that make up the foundation of the ocean food web. Phytoplankton also provide half of all the oxygen we breath—so thank phytoplankton for every other breathe you take. You can read more about phytoplankton and chlorophyll in our recent post.

Photography by Kevin Morris

Every hour and every day, the Continuous Monitoring Station—a.k.a our “Cage of Science”—is building a more complete picture of the seasons beneath the Bay. Thanks to support from Casco Bay Estuary Partnership and generous donors, the Station collects measurements of temperature, salinity, pH, dissolved oxygen, carbon dioxide, and chlorophyll fluorescence year-round. Every other week, Research Associate Mike Doan cleans and calibrates the equipment, and downloads and graphs the data to track conditions in the Bay.

Spring starts early in Casco Bay!

Our Continuous Monitoring Station chronicles the rise and fall of microscopic blooms in Casco Bay. This graph of chlorophyll fluorescence tells us that the spring bloom of phytoplankton beneath the ocean happens well before plants on land emerge from beneath the snow.

 

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 web. Like plants on land, they respond to increasing sunlight by bursting into bloom. By mid-February, daylight has increased by over an hour since December 21st, and the phytoplankton are flourishing.

Last January, 2017, there was an early bloom of phytoplankton in Casco Bay. How do we know? Friends of Casco Bay maintains an underwater sentinel that collects information about the water of the Bay every hour, 24 hours a day, 365 days a year. It is our Continuous Monitoring Station.

We will soon be crunching the January-February 2018 data, looking for confirmation of this year’s phytoplankton bloom.

A modified lobster trap houses a carbon dioxide sensor and a data sonde, electronic devices that continually take the pulse of the Bay. Together, they provide evidence of how our coastal waters may be changing over time. This long-term monitoring station, fondly known as “the Cage of Science,” is anchored just above the sea floor off Cousins Island in Yarmouth.

We now have over a year of hourly data on oxygen levels, carbon dioxide, pH (the level of acidity of the water), salinity, temperature, water clarity, water depth, and chlorophyll fluorescence, a measure that provides an estimate of phytoplankton abundance. Chlorophyll is the green pigment in plants that traps the energy of the sun for photosynthesis.

Phytoplankton provide food for the smallest zooplankton. These tiny floating animals are eaten by larger zooplankton, such as copepods, shrimplike creatures. Both phytoplankton and zooplankton are at the mercy of the currents, winds, and tides.

The data from the Continuous Monitoring Station documents the changes in the water’s chemistry as a result of these blooms. The net positive effect in Casco Bay over the course of the spring season is more oxygen and less acidic water, thanks to those early-blooming phytoplankton.

Beyond Casco Bay, in the Gulf of Maine, a circular current called a gyre distributes marine life around the Gulf. The gyre transports phytoplankton to where zooplankton are hatching, just in time to feed emerging copepods, which in turn feed baby fish, clams, and other sea creatures.

Success in the ocean food web, like in much of life, depends on being in the right place at the right time.

Our Continuous Monitoring Station has been in place for about a year and a half, too soon perhaps to provide data that might indicate whether or not Casco Bay’s food web is changing. Still, every hour and every day, our cage of science is building a more complete picture of the seasons beneath the Bay, giving us insight into how climate change may alter the food web of our coastal water in years to come.

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.

Volunteers do a great service to Casco Bay

Citizen Stewards received recognition for milestones in Water Quality Monitoring: John Todd, Michelle Brown, Debora Price, Sheila McDonald, Dick Stevens and Erno Bonebakker. Photograph by Kevin Morris

More than 125 volunteers and supporters of Friends of Casco Bay came to the Volunteer Appreciation Celebration on January 23to recognize those who give their time to monitor the water quality of the Bay, clean up shorelines, stencil storm drains, participate in community outreach events, and serve on its Board.

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At the event, ten Citizen Stewards received recognition for milestones in Water Quality Monitoring. Sarah Lyman, Community Engagement Coordinator for Friends of Casco Bay, recognized each of the honorees, remarking, “There is so much power and synergy in being able to connect data and connect people.”

 

Those recognized for their milestones in service:

Erno Bonebakker (25 Years)

Erno has been volunteering since 1993, the first full year of the Friends of Casco Bay’s water quality monitoring program. He and his family moved here from California in 1988, and within a week, Erno attended a meeting about the health of Casco Bay. His passion for Casco Bay has only deepened as he continues to explore, study, and care for it. He divides his time between Chebeague Island and Portland.

 

Dick Stevens (15 Years)

Dick Stevens has been active in the Gulf of Maine Ocean Racing Association and the Portland Yacht Club–winning a few trophies along the way. Sailing the coast and kayaking the lakes and rivers of Maine has given Dick a closer appreciation of the delicate nature of this rugged environment. This inspired him to volunteer as a Citizen Steward for Friends of Casco Bay.

 

Sheila McDonald and Debora Price (10 Years)

Sheila MacDonald and Debora Price have shared a sampling site at Mere Point Boat Launch in Brunswick, where they have found enthusiastic support whenever they explained why they were sampling the water quality of Casco Bay. Sheila serves as deputy director of the Maine State Museum. Debora is retired after teaching, owning a local real estate business, and co-founding an eldercare service, Neighbors, Inc.

 

Michelle Brown (5 Years)

Michelle has a professional background in wildlife management and natural resource conservation. Throughout her career, she has witnessed the power of volunteers and volunteering, so when she and her husband moved to Peaks Island, she was delighted to find out about the Friends of Casco Bay Citizen Stewards Program and how the data that volunteers collect provide important information about the Bay.

 

Craig Burnell (5 Years)

Craig always knew he wanted to become involved in the sciences, studying and learning about our environment. He works at Bigelow Laboratory for Ocean Sciences as a Research Associate in the Bigelow Analytical Services facility. When not working, he is likely to be training for his next bike race, which will include a race across the country this summer.

 

John Todd (5 Years)

John and his wife Cathie have summered in Phippsburg since the 1960s. They finally moved there full time in 2005 after John retired from a career in international development. They love living on The Basin, where they enjoy swimming and kayaking, especially with their grandchildren.

 

Jan Flinterman (5 Years)

Jan has shared coverage of a water quality site at The Basin, a saltwater inlet on the New Meadows River in Phippsburg, with John Todd and Jim Sidel. Data collected by Citizen Stewards helped convince the Maine Legislature to upgrade this popular anchorage to the highest level of water quality protection, Class SA.

 

Rob Sellin and Natalie West (5 Years)

Rob and Natalie spent many years sailing the world before arriving in Maine in 2011 aboard S/V Wilhelm, their 44-foot steel cutter. They settled in South Portland and have been sampling water quality at the pier at Southern Maine Community College since 2012. They sail the coast of Maine every summer, exploring the extraordinary bays and offshore islands of our state, often accompanied by their adult children and their grandchildren.

Keeping you up to date as we keep an eye on the Bay

Photograph by Kevin Morris

Casco Bay, like ocean water around the world, is changing and changing quickly.

We want you to know that we have changed our volunteer Citizen Stewards Program and our staff-led Water Quality Monitoring efforts in order to stay on top of the science of how the Bay may be changing.

When our organization started in 1989, no one knew the health of the Bay. That was the question we were asked—“How healthy is Casco Bay”—and that is what our first quarter-century of monitoring has enabled us to address.

Thanks to the data that hundreds of our volunteer Citizen Stewards have helped us collect over the past 25 years, in addition to data collected by our staff, we can identify where regions of the Bay are challenged, and where, generally speaking, the Bay is healthy. The snapshots of data volunteers collected are a key aspect of our Casco Bay Health Index and have been vital to our advocacy efforts. This 25-year data set has provided us with a solid foundation from which to launch this next phase of data collection.

Looking forward, our monitoring goals are to:

  • Understand how Casco Bay is changing with respect to climate change, ocean and coastal acidification, sea level rise, and other stressors
  • Conduct more intense data collection efforts in challenged regions of the Bay to try to understand why water quality is so poor, in places such as Portland Harbor and the mouth of the Harraseeket River
  • Involve more volunteers in our efforts to keep Casco Bay blue. While we are utilizing more technology to help us achieve our first two goals, technology will never replace the connections, energy, visibility, and goodwill that volunteers like you provide as ambassadors for the Bay.

In order to meet these goals, we are now monitoring Casco Bay through these four ways:

  1. Our Continuous Monitoring Station collects hourly data to help us address the question “How is Casco Bay changing?” We launched this station more than a year ago, and we are excited about how much we have learned about the Bay in a short time. We intend to keep this Station operating in perpetuity.
  2. Using data sonde technology, our staff will continue to collect data at 12 legacy volunteer Citizen Steward sites—these sites were chosen as representative of regions around the Bay and include healthy sites, challenged sites, and those in between. We think of this monitoring as “the Bay getting a checkup.” How are regions of the Bay doing? Are healthy areas remaining healthy? Are challenged areas continuing to show problems, or might they be improving?
  3. Using our Baykeeper boat, our staff will conduct more intensive efforts in challenged regions of the Bay. If you have seen our Health Index, you have seen that there are “red dot” areas. We are looking closer at those red dot areas and asking, “what may be causing the trouble?” We began this work in 2017, as we conducted transects, from surface to bottom, and across regions, in Portland Harbor and in the Harraseeket River. We will continue to look intensively at these regions.
  4. Using volunteer citizen scientists, we will engage the community to help us collect data and observations on a changing Casco Bay. Our volunteer program is going through a large transition. We are significantly changing the time commitments required to become a citizen scientist, and we are changing the parameters that volunteers collect. We will be asking Citizen Steward Volunteers to collect new kinds of data and record observations on changes in Casco Bay.

In 2016, you may remember that we organized a citizen science “flash mob to Nab Nitrogen.” The event was an incredible success, signaling that there is a huge reservoir of goodwill from people who want to help protect the health of the Bay and are willing to do that in short bursts of data collection efforts. We learned that we can count on our community to help us grab vast amounts of data if we make sampling easier and reduce the time commitment.

For example, we are piloting having volunteers measure the color of our waters as a biological indicator. The general public often considers blue water to indicate healthy oceans and dirty-brown water to indicate polluted water. In fact, scientists attest to color being an excellent indicator of what is happening in our oceans. For more than a century, marine scientists have used the Forel-Ule scale to document the color of oceans and lakes.

The color of our water, measured by this scale, can be an excellent environmental indicator. By using a specially designed smartphone app and a secchi disk, volunteers can help us collect scientific data on the color and clarity of our waters. The protocols for this data collection are easy to follow, and the data helps address a question we often hear: “How is the Bay changing?”

We will also ask volunteers to help us observe and keep track of nuisance and harmful algal outbreaks, which have plagued our waters these past two summers.

By revamping our volunteer monitoring efforts, we have the opportunity to broaden our network of knowledgeable ambassadors for our coastal waters—and make strides in our understanding of the Bay.

In our experience, our volunteers are some of the most active, outspoken, and well-spoken members of our community. We look forward to engaging more volunteers than ever this year. The commitment of these volunteers will send ripple effects through towns around the Bay.

The looming question for the future— How is Casco Bay changing?

Photograph by Kevin Morris • Aerial support provided by LightHawk

We see water itself as fundamental habitat. When water quality deteriorates, eelgrass, plankton, clams, and other marine creatures suffer. Thanks to our 25-year data set on water quality in Casco Bay, we now have a better overall understanding of the health of the Bay. We understand when and which areas of the Bay are likely to exhibit challenged water quality conditions.

Armed with this baseline data, we can now begin to address the question How is the Bay changing?—thus, the establishment last year of our first automated Continuous Monitoring Station. We will also continue to monitor selected sites at the surface, to supplement the historical data set compiled by our Citizen Stewards Program. And, we will look more intensively, using surface-to-bottom transects, at those regions of the Bay which present challenged conditions. New data and observations may help us begin to understand how climate change, excess nitrogen, and the changing chemistry of Casco Bay may be impacting the ocean food web.

Our Nabbing Nitrogen event in 2016 signaled to us that there is a huge reservoir of goodwill from people who want to help protect the health of the Bay and are willing to do that in short bursts of data collection efforts. We foresee new volunteer opportunities in this type of data collection, as well as in expanding other community service projects, such as coastal clean-ups, storm drain stenciling efforts, and issue-education events to inspire Champions for the Bay.

Citizen Steward volunteers will continue to be key to our organization as they help us move into this next phase of work to improve and protect the environmental health of Casco Bay. Casco Bay belongs to all of us, and this Bay is fortunate to have so many Friends.

Cathy L Ramsdell, CPA, CGMA
Executive Director

Cathy Ramsdell Interview

What we have learned from 25 years of water quality data

Since 1992, more than 650 volunteers have gotten their hands wet in our Citizen Stewards Water Quality Monitoring Program, complementing the work of our staff scientists in assessing the environmental health of Casco Bay. This science is the foundation of much of our community engagement and advocacy efforts.

Volunteer Citizen Stewards measured dissolved oxygen, temperature, salinity, water clarity, and pH at nearly 40 shoreside sites on the same date and time on ten Saturdays from April through October, to create a simultaneous snapshot of surface conditions around the Bay.

Our staff scientists have monitored offshore at 10 stations, from surface to sea floor, aboard our research vessel, every month of the year.

The data allowed us to address these questions:

  • How healthy is the Bay?
  • Where are problem areas?
  • What influences the health of the Bay?

 

What we have learned

  • Casco Bay is generally healthy, compared with other estuaries.
  • Year after year, our data has identified Portland Harbor, the New Meadows embayment, and the mouth of the Harraseeket River as the most environmentally challenged areas in Casco Bay.
  • The healthiest regions of the Bay are Broad Sound, Maquoit and Middle bays, and the offshore waters near Halfway Rock.
  • By sampling both along the shore and offshore, we determined that land-based origins contribute significant sources of excess nitrogen.
  • The bottom water of the Bay has become more acidic, a worrying trend that mirrors what is happening worldwide.
  • Summer is lasting longer beneath Casco Bay. Water temperatures are staying warmer into the fall.
  • In order to better understand how the Bay is changing, we are increasing the frequency of data collection.

Volunteer Appreciation & Annual Member’s Meeting

Friends of Casco Bay’s 2016 Volunteer Appreciation Celebration & 2018 Annual Members Meeting

Volunteer Appreciation Celebration
& 2018 Annual Members Meeting

Thank you all for a great event! You can see more about our Citizen Steward awardees and the photos here: https://www.cascobay.org/2018/01/25/volunteers-great-service-casco-bay/

Join us as we recognize those who help us protect the health of Casco Bay. We will provide the updated Casco Bay Health Index based on data collected by volunteer Citizen Stewards over the past 25 years, and we will share new program directions.

When: Tuesday, January 23, 2018, 5:30-8 p.m.
5:30 Hors d’oeuvres, cash bar, Program begins at 6:30

Our event is on for Tuesday, January 23! We have been watching the weather closely—the messy wintery mix will turn into rain and 40 degree weather by midday on Tuesday, January 23, and temps will stay in the 40s until well past our event.

Parking is easy and FREE at DiMillo’s—if you are driving with guests, you can drop your passengers off right at the ramp under the drive-thru overhang leading to the floating restaurant.

WhereDiMillo’s On the Water, 25 Long Wharf, Portland, ME 04101
Free parking while at event.

Donation to attend is appreciated, not required. Suggested donation: $10 per person
If making a donation to attend this event, RSVP here

If you want to RSVP without making a donation, email Sarah Lyman at slyman [at] cascobay [dot] org or call our office at (207) 799-8574.

 

Continuous Monitoring Station

Monitoring a Changing Casco Bay 365 Days a Year

Continuous Monitoring Station
When we haul up the Continuous Monitoring Station to download data and recalibrate the equipment, we also track marine creatures that may have found a home on our “cage of science.”

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 is our Continuous Monitoring Station, which will help us answer the question “How are our coastal waters changing over time?” Research Associate Mike Doan calls it “the cage of science.”

It has been just over a year since we placed a carbon dioxide sensor and a data sonde—an electronic device that records temperature, pH, and other characteristics of water quality—inside this modified lobster trap and moored it in healthy waters near the center of Casco Bay off Cousins Island in Yarmouth.

After one full year, we have over 8,760 hours of data on oxygen levels, carbon dioxide, pH (the level of acidity of the water), salinity, temperature, chlorophyll fluorescence (estimated phytoplankton abundance), water clarity, and water depth.

Thanks to our 26-year data set on water quality in Casco Bay, we understand when and which areas of the Bay are likely to exhibit challenged water quality conditions that require further study. Armed with this baseline data, we can now consider how to address the question, How is the Bay changing?

The steady flow of data from the Station already is helping us detect and document how climate change and emerging coastal stressors may be affecting the Bay. Hourly data helps us identify daily, seasonal,
and annual trends to better understand the extent to which ocean acidification may be impacting the water chemistry of Casco Bay. In future years, we hope to deploy two more “cages of science,” one in challenged waters in Portland Harbor and one near Harpswell to help detect the influence the Kennebec River has on Eastern Casco Bay.

What is a data sonde?
A data sonde, such as the one being used by Research Associate Mike Doan, is an oceanographic
monitoring instrument that takes multiple measurements of water quality simultaneously. In
addition to being used as part of our Continuous Monitoring Station, data sondes are used by
staff scientists in other water quality monitoring efforts from shore and by boat. The data is
downloaded to a computer and analyzed to provide a long-term picture of water quality over
time. We thank Casco Bay Estuary Partnership and our generous members for helping fund
our Continuous Monitoring Station’s first year.

 

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.

2016 Casco Bay Health Index

Casco Bay Health Index – Updated with 2016 data

2016 Casco Bay 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.

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.