A method for quantifying the number of U.S. lakes with cyanobacterial harmful algal blooms using satellite remote sensing

Cyanobacterial harmful algal blooms are the most common form of harmful algal blooms in freshwater systems throughout the world. However, in situ sampling of cyanobacteria in inland lakes is limited both spatially and temporally. Satellite data has proven to be an effective tool to monitor cyanobacteria in freshwater lakes across the United States. This study uses data from the European Space Agency MEdium Resolution Imaging Spectrometer and the Sentinel-3 Ocean and Land Color Instrument to provide a national overview of the percentage of lakes experiencing a cyanobacterial bloom on a weekly basis for 2008-2011 and 2017. A total of 2,370 lakes across the contiguous United States were included in the analysis. Bloom percentage was calculated for nine United States climate regions to examine regional patterns. Changes in cyanobacterial bloom percentage followed the well-known temporal pattern of freshwater blooms. The percentage of lakes experiencing a bloom increased throughout the year, reached a peak around October, and decreased through the winter. Wintertime data, particularly in the northern latitude regions, was consistently limited due to snow and ice cover. With the exception of the Southeast and South climate regions, regional patterns mimicked patterns found at the national scale. The Southeast and South regions exhibited an unexpected pattern as cyanobacterial bloom percentage peaked in the winter rather than the summer. Several environmental factors and potential satellite limitations can possibly explain these findings. Results from this research can help establish a baseline of annual occurrence of cyanobacterial blooms in inland lakes across the United States.