Assessing Cyanobacteria Blooms from Space

Frequent occurrence of cyanobacterial harmful algal blooms (CyanoHABs) has drawn support for more frequent and synoptic observation and assessment of inland-lake water quality. In this study, we present spatiotemporal dynamics of CyanoHABs in Continental United States (CONUS) lakes by using a bloom magnitude metric. We estimated bloom magnitude as the spatiotemporal mean of satellite-derived areal CyanoHAB biomass, which was calculated from Medium Resolution Imaging Spectrometer (MERIS) and Ocean Land Color Imager (OLCI) observations. CyanoHAB magnitudes in all satellite-resolvable CONUS lakes were calculated for the MERIS (2003-2011) and OLCI (2016-present) time series. In total, 2,369 lakes were resolved in MERIS/OLCI data, with the majority of these lakes in Minnesota, Maine, Michigan, Texas, and Florida. About 40% of all the lakes had CyanoHAB magnitude in the high risk category, as per World Health Organization guidelines using only biomass, comparable to the one-third of lakes in the National Lake Assessment with cyanotoxins present. These lakes with CyanoHAB issues were found in all regions of the country. We also complemented this analysis by integrating other published bloom metrics such as the spatial extent and temporal frequency to draw actionable insights about the bloom, which may be usable by water-quality managers to prioritize lake management strategies. The proposed framework may serve as a national-level CyanoHAB screening tool for larger lakes, and would allow for annual evaluation of recreational and drinking water lakes.