Friends of Casco Bay is a nonprofit marine stewardship organization. Through science, advocacy, and community engagement, the organization has been working to improve and protect the health of Casco Bay since 1989. Friends of Casco Bay has monitored water quality through discrete sampling around the Bay for 30 years. The pace of climate change has necessitated the addition of automated continuous monitoring. Since 2016, one continuous monitoring station has been deployed near the middle of the Bay. Year-round, hourly data collection has provided the increased frequency needed to observe the daily, seasonal, and annual variability inherent in coastal systems. This rigorous approach is necessary for long-term tracking of change in the Bay. The goals of the continuous monitoring station include identifying seasonal variability and potential drivers of carbonate chemistry and documenting change in the water quality of the bay. Understanding current conditions and tracking change allows Friends of Casco Bay to more effectively raise awareness of, and advocate to address, climate change. The station collects hourly measurements of depth, temperature, salinity, dissolved oxygen (DO), chlorophyll, turbidity, pH and the partial pressure of carbon dioxide (pCO2). The pCO2 is measured with a Turner/Pro Oceanus C-Sense sensor via a PME data logger. All of the other parameters are collected with a YSI EXO 2 data sonde. Dissolved inorganic carbon, total alkalinity, and omega aragonite are derived from temperature, salinity, depth, pH, and pCO2 data, using the CO2SYS program.

Every two to three weeks, the data sonde and the pCO2 sensor are exchanged for clean, calibrated instruments. In this way, biofouling is dramatically reduced and data quality and continuity are ensured. The instruments are suspended in a modified lobster trap. The trap rests on the bottom in about 2-5 meters of water, depending on the tide. The instruments are fixed at about 0.3 meters off the bottom. The station is located near the middle of the bay at a site representative of much of the bay, with strong flushing and historically good water quality.