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Seasonal Sampling Across Casco Bay

Monitoring Surface Waters and the Water Column

Friends of Casco Bay’s Monitoring Program 

We maintain and continue to add marine water quality data to one of the largest and most important long-term data sets in New England.  The work we do today builds on our 26-year data set. We continue to monitor 22 sites on a regular basis to maintain seasonal, spatial coverage of Casco Bay, and, we have added a continuous monitoring station that collects data hourly, year-round.

How our data are used

Our science is essential to our advocacy and community engagement. Our data have been used for many purposes, large and small, by our staff and other organizations, agencies, researchers, and individuals. Our data continue to:

  • Ensure better long-term protections for the health of the Bay
  • Regulate and reduce pollution through state-issued discharge permits
  • Influence legislation and ordinances
  • Inform our community engagement
  • Identify challenged conditions in areas of the Bay where further study is needed
  • Advance science in Maine and throughout the Gulf of Maine
  • Assist in the education of our future oceanographers and marine scientists
  • Enable state and federal governments to document the health of Maine’s coastal waters
  • Assist others in innovative ways

Learn more about our data and how they have been used here.

How are we collecting data? What information is collected?

We use a YSI data sonde to measure temperature, salinity, dissolved oxygen, pH, 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.

A data sonde is an electronic monitoring device that can collect several parameters of water quality at once, using various carefully-calibrated sensors, thus making our data collection faster and more comprehensive. The data are downloaded to our database and then analyzed.

Water clarity (or Secchi depth) is determined by Secchi disk. Water samples are collected for analyses of levels of total nitrogen (TN) and dissolved organic nutrients (DIN).

See the surface data collected at all 22 sites.

The map shows data collected by Friends of Casco Bay staff using a data sonde and a Secchi disk, at 22 locations during our 2018 sampling season. Every few weeks from May through October, this the spatial, episodic data is collected at the surface and at profile sites as described above. The data are uploaded to this mapping tool just a few days after each sampling event, allowing you to view our most current data.

We encourage you to click on each dot to see our latest measurements. To see the data in more detail, click on a graph for a specific parameter. From there, you can also click on the button just above the dot graph (see example to the right) to read a description of the parameter.

One note: This mapping tool refers to “trends,” but these are really just the changes we have seen since May of this year. One sampling season does not provide enough data to meet the scientific analytic standard needed for a true trend. The data we collect through our Continuous Monitoring Station are building the long-term data set that we will be able use to analyze trends in the future.

Questions about the Bay  

Our Water Quality Monitoring, launched in 1993, initially was designed to address:

How healthy is the Bay? Where are the problem areas?

Spatial, episodic monitoring by staff and volunteers provided a “snapshot” of the environmental health of the Bay. From 1993-2017, staff scientists collected water quality data from the surface to the bottom, every month, at ten profile sites across Casco Bay. Volunteer Citizen Stewards sampled surface sites from shore, from April through October, using Secchi disks and water quality test kits specifically designed by us as “Casco Bay kits.”

This long-term monitoring has provided critically important baseline data and showed that the water quality of certain areas of the Bay has consistently remained healthy or challenged. After more than 25 years, we realized we were not learning new information. Given the constraints of time and funding, we assessed options and determined that we needed to shift our efforts to engage volunteers in new, more inclusive efforts, while significantly increasing the amount of data collected by staff using modern technologies.

 Learn more about the history of our Water Quality Monitoring Program  and our historic Citizen Steward Water Quality Monitoring Program.

We changed our Water Quality Monitoring Program in 2018 in order to address a new question: How is the Bay is changing?

This question inquires about trends in data, and detecting trends requires robust data sets.

In order to collect statistically-sound data, we needed to increase the frequency of our monitoring.

Episodic snapshots of the Bay cannot provide enough data to address the question: How is Casco Bay changing? More comprehensive, continuous data 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 water quality monitoring allows us to:

  • Continue to provide spatial and periodic coverage of the entire Bay
  • Collect data on additional parameters (total nitrogen, dissolved organic nutrients, and chlorophyll) at historic Citizen Stewards monitoring sites
  • Do more intensive examination of challenged areas
  • Collect continuous data

Continuing to collect episodic data at historic water quality sites

Our staff scientists continue to add to our important long-term data set by collecting data at the surface and at profile sites at 22 locations every three weeks from May through October. The stations are representative of different regions of the Bay, and water quality sites range from “healthy” to “challenged.” Staff can measure water quality in seconds using a data sonde, an electronic monitoring device that can collect several parameters of water quality conditions at once.  

Staff members visit these sites by land and by boat. Being on or near the water regularly provides our scientists and other staff the opportunity for frequent, first-hand views of conditions around the Bay. In addition to collecting data on water quality, we record observations of weather, sea state, wildlife, and unusual sightings and conditions.

More people are seeing the Casco Baykeeper/Friends of Casco Bay logo on our Baykeeper vessel and Baykeeper truck as we travel around the Bay. Increasing our visibility allows us to engage more often with locals who share with us information or concerns about what they are seeing on the Bay.

Monitoring Surface Waters

Of the 22 seasonal locations we monitor, 13 were chosen specifically to continue taking “snapshots” of data. This allows us to continue to build on this foundational data set of spatial conditions at 13 historic Citizen Stewards sites, over a broad range of conditions around the shoreline of the Bay, from South Portland to Harpswell and Brunswick. We visit these sites every three weeks from May through October.

Monitoring the Water Column—Profile Sampling

Our staff scientists collect water quality data from the deck of the Baykeeper boat. We monitor at 9 stations, collecting data at the surface, at one meter, and then every two meters to the bottom, to create a “profile” of the water column. These sites are monitored every three weeks from May through October.

The sampling is conducted in five regions. Three are individual profile sites that we have been monitoring for over a quarter of a century. These profiles are conducted at our three original sentinel sites (Clapboard Island, Fort Gorges, and Broad Sound). We continue to add to the long-term data sets on these sites which were monitored monthly, year-round, from 1993 to 2017.

Surface sampling by our Citizen Stewards, from 1993-2017, helped identify the Harraseeket and Fore River/Portland Harbor regions as challenged areas of the Bay. Currently, we collect data using three profile sites along transect lines, in each region. The Harraseeket and Fore River regions often have low dissolved oxygen, high chlorophyll, high nitrogen, low pH, or some combination, indicating challenged water quality. We are looking deeper for hints as to what causes these areas to have poor water quality. The transects provide better insight into water quality dynamics in each area.

You can help us keep Casco Bay blue

Learn more about our data and how it is used here.