Technical note—Performance evaluation of the PhytoFind, an in-place phytoplankton classification tool

In 2019, the U.S. Geological Survey evaluated the performance of the Turner Designs, Inc. PhytoFind, an in-place phytoplankton classification tool. The sensor was tested with sample blanks, monoculture and mixed phytoplankton cultures, and turbidity challenges in a laboratory, and was tested on a 120-mile survey of the Caloosahatchee and St. Lucie Rivers in Florida, including Lake Okeechobee. Results include the following:

• The mixed phytoplankton group fluorescence channel (green excitation sensor) of the PhytoFind can be sensitive to interference.
• The PhytoFind generally overestimated chlorophyll concentration relative to laboratory-measured chlorophyll a concentrations.
• Turbidity interference may be less apparent in samples where green algae (chlorophytes) represent a high relative percentage of biovolume.
• The dissolved organic matter compensation feature was effective in the environmental waters sampled during this evaluation.
• The correlation between percent chlorophyll contribution per phytoplankton group measured by the PhytoFind and relative percent biovolume per phytoplankton group measured in the laboratory varied and was not explicitly determined to be related to dominant taxa, phytoplankton community composition, or environmental conditions.