What does the data tell us?

Posted on Apr 20, 2011

Frank Leavitt hauls a bucket of water to begin sampling.

Frank Leavitt hauls a bucket of water to begin sampling.

Darren McLellan and 77 other citizen scientists logged over 1,800 hours for Friends of Casco Bay last year alone. Our volunteers have been testing the water quality from Phippsburg to Cape Elizabeth for the past 19 years. For the past 6 years, they have been sampling twice a day, at 7 a.m. and at 3 p.m.

 

Research Associate Mike Doan analyzes the data that Friends of Casco Bay has amassed. “I know of no other program in the country that asks its volunteers to sample twice a day. This provides a unique opportunity to assess daily fluctuations in dissolved oxygen, temperature, salinity, pH, and dissolved inorganic nitrogen. Our data shows that water chemistry is clearly impacted by the cycle of photosynthesis, respiration, and decomposition of the microscopic plants called phytoplankton.”

 

In a general sense, the water quality of the Bay is lower in the morning and higher in the afternoon. Throughout the day, phytoplankton absorb sunlight and photosynthesize, releasing oxygen into the water. At night, the process is reversed; phytoplankton absorb oxygen from the water.

 

Peter Milholland says, “This work is groundbreaking. We never knew until we started testing twice a day how all the parameters would change from morning to afternoon. Water quality typically changes from a ‘worst case’ to a ‘best case’ scenario as the day progresses. Knowing that helps us better understand the rhythm of the Bay.”

 

In a general sense, the water quality of the Bay is lower in the morning and higher in the afternoon as oxygen levels in the water increase, pH rises, and nitrogen content decreases.

 

Some areas of the Bay experience dramatic daily swings in oxygen, pH, and nitrogen levels. Often these regions, such as narrow embayments in eastern Casco Bay, are where we find substantial crops of phytoplankton thriving in the water column. When these phytoplankton die and decay, the bacteria that break them down consume oxygen from the water, which other marine life needs. Decomposition of these marine plants can also release more carbon dioxide, raising the acidity of the sea water. This makes it harder for baby clams and other shellfish to build their protective shells.