Assessing Plankton Trends in Great Pond Using FlowCAM® Technology

By Marianne Ferguson ’14, Savannah Judge ’15, Sarah Large ‘14

Sarah Large ('14) enjoying a sunny day at work on the lake.

Sarah Large (’14) enjoying a sunny day at work on the lake.

As you may have seen in previous blog posts, Colby College recently deployed a high frequency monitoring buoy into Great Pond, affectionately known as Goldie, that relays environmental data to the website every 15 minutes. Two features of this buoy are the photosynthetically active radiation sensor and the fluorescence meter. These sensors can be used to understand variations in phytoplankton abundance due to the relationship between sunlight, the chlorophyll plankton contains, and the fluorescence plankton emits. Plankton are an important indicator of lake water quality and they form the base of the freshwater food web. However, the buoy and its sensors are stationary, which begs the question of whether or not Goldie’s data is representative of plankton populations in other parts of the lake. So, to test the reliability of these sensors as measures of phytoplankton biomass we are making weekly collections of water at various depths below the surface of Great Pond at the buoy and four other sampling sites.

Student research assistants on the lake, collecting data

Student research assistants on the lake, collecting data

To analyze the water samples for plankton, we use a FlowCAM. According to Fluid Imaging Technologies, Inc., the company that developed the FlowCAM, it is: “an integrated system for rapidly analyzing particles in a moving fluid. The instrument combines selective capabilities of flow cytometry, microscopy, and fluorescence detection. The FlowCAM automatically counts, images, and analyzes particles or cells in a sample or a continuous flow.” Basically, a pump draws water from the sample through a flow cell while laser technology monitors the fluorescence and light scatter of particles in the sample. If the particle triggers the laser with enough fluorescence or light scatter, the camera takes a picture. The images, as well as fluorescence and scatter properties, are saved within the FlowCAM’s computer program.

Image of a copepod from the FlowCam.

Image of a copepod from the FlowCam.

Using these images, we can assess the concentration and diversity of the plankton in our water samples. These weekly surveys can then be compared to relevant sensor data in order to calibrate the relationship between fluorescence and actual phytoplankton concentration. We are also studying zooplankton trends in conjunction with phytoplankton. Zooplankton are predators of phytoplankton and the two groups often have coupled population cycles. Going forward, we hope to classify the species in each sample, determine their ecological significance, and track population trends. This calibration and tracking of trends may allow us to understand and predict algal blooms from Goldie’s data.

Marianne Ferguson ('14, Colby College) at work on the Compass

Marianne Ferguson (’14, Colby College) at work on the Compass

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