Comparing Field Data with Satellite Imagery to Improve Management of Toxin-Producing Cyanobacteria Blooms in Lakes

Abstract:

Increasing public concern has directed regulatory agencies in the United States to improve detection and mitigation of toxin-producing cyanobacteria blooms in freshwater ecosystems. The analysis of satellite imagery provides a promising, cost-effective method to help achieve these goals. However, water quality managers need a high degree of confidence that satellite derived data provide an accurate portrayal of bloom events. Here, we compared in situ time series data with data collected by the Sentinel 3 Ocean and Land Colour Instrument (OLCI) to assess how well satellite imagery captured the timing and magnitude of toxin-producing cyanobacteria blooms in a lake with high recreational value. During the summer of 2019, we monitored temperature, dissolved oxygen, chlorophyll a, phycocyanin, and pH at 15-minute intervals from 26 June to 19 September 2019 in Odell Lake, a eutrophic lake in the Cascades Mountains of central Oregon, USA that frequently experiences blooms of toxin-producing cyanobacteria from the genus Dolichospernum. For comparison, we monitored Crescent Lake, an oligotrophic lake in the same physiographic setting. We acquired corresponding OLCI-derived cyanobacteria cell counts from the US Environmental Protection Agency CyAN project. The Oregon Department of Health issued a public health advisory for the toxin microcystin in Odell Lake from August 2^nd to 18^th, 2019, whereas Crescent Lake remained bloom free during the study period. The in situ data indicated cyanobacteria bloom formation in Odell Lake two weeks prior to the issuance of the advisory, corresponding to when minimum daily surface water temperatures rose above 16 °C. Satellite derived cyanobacteria cell counts exhibited the same temporal pattern as in situ data for both lakes, although estimates were inherently more sporadic. Our results suggest that increasing the use of satellite-derived information can help water quality managers improve the timing of public health advisories for blooms of toxin-producing cyanobacteria and help identify lake conditions and watershed factors that trigger blooms.