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Continuous Monitoring Station

Imagine Working 365 Days a Year.

Friends of Casco Bay is doing just that, using technology in our Continuous Monitoring Station. The station consists of a data sonde, an instrument that can measure several properties of water at once, and a separate device that measures carbon dioxide. These electronic devices are secured together in a repurposed lobster trap on the ocean floor. This station, located off Yarmouth near the coastal midpoint of Casco Bay, was launched in 2016. The station collects data once an hour, every hour, year round.

Long-term data sets, collected hourly, are proving indispensable to monitoring the changing health of Casco Bay. These data not only support our advocacy and education efforts, but also inform the work of other scientists, government officials, and activists working to protect the health of Casco Bay.

Continuous Monitoring Station Data

Monthly Mean Graphs

Click on the parameter below (in the blue boxes) to see monthly mean values based on the data and measurements we are collecting. We add data to these graphs monthly to document changes in water quality conditions in Casco Bay.

Temperature

Water Temperature in Celsius (C)
The temperature of the water, measured in degrees Celsius. The growth, reproduction, and survival of marine life are influenced by temperature.

Salinity

Salinity in parts per thousand (ppt)
Salinity is the saltiness of seawater — the amount of salts dissolved in water, measured in parts per thousand. The open ocean averages 35 ppt (that is 3.5% saltiness) and the Casco Bay estuary typically ranges from 5 to 33 ppt. Salinity levels are influenced by tides and the volume of fresh water and runoff flowing into the Bay. Marine life in estuaries such as Casco Bay normally can tolerate a larger range of salinity than those living in the open ocean.

Dissolved Oxygen

Dissolved Oxygen in milligrams per liter (mg/L)
Dissolved oxygen (DO) measures how much oxygen is available to marine life. When the concentration of Dissolved Oxygen falls below 5.5 mg/L (5.5 milligrams of oxygen dissolved in one liter of seawater), fish and other marine life can become stressed. Dissolved Oxygen levels less than 2.0 mg/L may be life-threatening to marine animals.

Dissolved Oxygen % Saturation

Dissolved Oxygen Percent Saturation (%)
Dissolved Oxygen Percent Saturation is a measure of oxygen. When water holds all the oxygen it can at a given temperature and salinity, it is said to be 100% saturated. Dissolved Oxygen Percent Saturation compares the actual dissolved oxygen concentration compared to the theoretical 100% saturation of dissolved oxygen concentration under the measured temperature and salinity conditions.

Chlorophyll

Chlorophyll Fluorescence in micrograms per liter (µg/L)
Measurements of chlorophyll—the green pigment that enables plants to photosynthesize—provide an estimate of phytoplankton abundance. Phytoplankton are the tiny marine plants that are at the bottom of the ocean food chain.

pH

pH

pH is a measure of the acidity of seawater. As more carbon dioxide is absorbed by the ocean from the burning of fossil fuels and the decomposition of marine plants, the pH of the water drops, becoming more acidic. Ocean acidification threatens the ability of marine life such as clams, mussels, and oysters, to grow healthy shells. Pure fresh water has a pH of 7; typically, seawater pH is between 7.5 and 8.4. Casco Bay receives a lot of fresh water and runoff, resulting in lower pH measurements.

Partial Pressure of Carbon Dioxide
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Partial Pressure of Carbon Dioxide in parts per million (pCO2)

Partial Pressure of Carbon Dioxide is a measure of the amount of Carbon Dioxide dissolved in the water, which varies with alkalinity, latitude, depth, and temperature. In addition, marine plants can add carbon dioxide to the water through respiration and remove it via photosynthesis. Dissolved Carbon Dioxide can also be exchanged with the atmosphere. Data on carbon dioxide, which has an impact on the acidity of our coastal waters, support our work to protect the health of Casco Bay.

Total Alkalinity

Total Alkalinity* in millimoles per kilogram (mmol/kg)

Total Alkalinity is a measure of the buffering capacity of the water, indicating how resistant the ocean is to acidification.

Dissolved Inorganic Carbon

Dissolved Inorganic Carbon* in millimoles per kilogram (mmol/kg)

Dissolved Inorganic Carbon is the sum of the concentrations of Carbon Dioxide, Carbonate, and Bicarbonate in the water. This is one of the parameters that provides a more complete picture of acidification in the Bay. 

Omega Aragonite

Omega Aragonite*

Omega Aragonite assesses the state of calcium carbonate in suspension in the water. Calcium carbonate is the material that marine life such as clams and oysters use to build their shells. When the level of Omega Aragonite in seawater falls below 1.5, it can be difficult for shell-bearing marine organisms to build and maintain their shells.

*Total Alkalinity, Dissolved Inorganic Carbon and Omega Aragonite are calculated from measurements of Temperature, Salinity, pH and pCO2 using CO2SYS software.

Understanding a Changing Casco Bay

The flow of hourly data that our Continuous Monitoring Station collects helps us detect and document how climate changes and other emerging coastal stressors may (or may not) be affecting Casco Bay. The amount of data collected—high frequency data—allows us to statistically “crunch” the numbers with better levels of scientific veracity than simply taking the occasional snapshot of conditions. While the snapshots are also important for monitoring the health of the Bay, this hourly data set can help us identify daily, seasonal, and annual trends and better assess the extent to which ocean acidification may be impacting the water chemistry of the Bay.

By deploying the data sonde and carbon dioxide sensor, we are able to collect hourly data on temperature, salinity, dissolved oxygen, pH, chlorophyll, and carbon dioxide (partial pressure). While vital in and of themselves, these measurements can also be used to calculate additional parameters, such as alkalinity, dissolved inorganic carbon, and calcium carbonate saturation state. By looking at these additional, calculated parameters, we get a more complete picture of acidification in the Bay. When we check the station to download data and swap out the equipment with freshly calibrated sensors, we also measure the color of the water, as well as Secchi depth, we collect nutrient samples for lab analysis, and we note marine critters (including invasive species) present in the trap.

This station, located off Yarmouth near the coastal midpoint of Casco Bay, was launched in 2016. Long-term data sets, collected hourly, are proving indispensable to monitoring the changing health of Casco Bay.

What We Are Learning

Research Associate Mike Doan nicknamed our monitoring station “the cage of science.” Having more data on carbon dioxide, which has an impact on the acidity of our coastal waters, not only supports our advocacy and education efforts, but also informs the work of other scientists, government officials, and activists working to protect the health of Casco Bay.

Periodically, we post findings and updates, based on data from the station, which you can find below.

More from our Continuous Monitoring Station

See what is going on beneath the surface. Check out our data!

January 23, 2019

On July 20, 2016, our Continuous Monitoring Station began recording data hourly, 365 days a year. We are excited to share the first two and half years of data, collected at our water quality monitoring site in Yarmouth, near the coastal midpoint of Casco Bay. We will update these graphs monthly, so come back… Read more

Water Temperatures Are Changing in Casco Bay

November 13, 2018

Friends of Casco Bay’s newest workhorse—our Continuous Monitoring Station (CMS)—has been amassing hourly data on the health of the Bay for over two years now. Research Associate Mike Doan is excited to be able to look at the daily, weekly, and seasonal changes in the Bay in far more detail… Read more

See sea critters and our Cage of Science

August 24, 2018

Watch this short video about the Cage of Science! You may know that Friends of Casco Bay’s Continuous Monitoring Station—AKA our “Cage of Science”—gives us vital data about the health of the Bay. But did you also know that observations of what sea life is growing on and hanging out… Read more

The Care and Maintenance of Our Submerged Monitor

Research Associate Mike Doan prepares our Continuous Monitoring Station for cleaning and re-calibration.

The only way to collect reliable data is to employ impeccable data collection methods. To that end, Mike swaps out the data sonde with freshly calibrated sensors, on a rigorously adhered to schedule. Our goal is to be able to capture 8,760 hourly data sets each year, or as close to that as equipment conditions allow.

Mike hauls up the anchored cage of devices and uploads to his laptop the data from the carbon dioxide sensor. He scrapes off marine hitchhikers, such as sea stars, tunicates, and algae, and makes note of any invasive species attached to the equipment or the cage. He often exclaims “It is amazing how fast sea creatures occupy any available surface under water, including our instruments!”

He swaps the data sonde for the one with freshly calibrated sensors, and checking to make sure the devices are secured, he then lowers the cage back onto the ocean floor. The retrieved data sonde is brought back to our lab, the data is downloaded and housed, and the sonde and its sensors are cleaned, soon to be re-calibrated for re-deployment. Such attention to detail provide quality assurance about the accuracy of the data.