Citation:

Whitman, P., B. Schaeffer, W. Salls, M. Coffer, S. Mishra, B. Seegers, K. Loftin, R. Stumpf, AND P. Werdell. A validation of satellite derived cyanobacteria detections with state reported events and recreation advisories across U.S. lakes. Harmful Algae. Elsevier B.V., Amsterdam, Netherlands, 115:102191, (2022). https://doi.org/10.1016/j.hal.2022.102191

Impact/Purpose:

Satellite-based monitoring and methods may serve as a complement to traditional in situ methods by providing frequent synoptic observations of cyanoHABs that are standardized across space and time. The primary objective of this study was to examine the agreement between a satellite-based approach for cyanoHAB monitoring with state reported cyanoHAB events and advisories. This is the first study to quantitatively evaluate satellite algorithm performance for detecting cyanoHABs with state reported events and recreation advisories. The combined NRDC events and state recreation advisories represented a broad geographical distribution across the US commensurate with previously reported human and animal cyanobacterial exposure. This study found that CI_cyano detected cyanobacteria presence during 60% of the NRDC events and 69% of the state recreation advisories. CI_cyano also detected a reduction or absence in biomass after 76% of the advisories were lifted. The algorithm had an overall agreement of 73% with state advisories, and, while the effect sizes varied from small to large, CI_cyano bloom frequency, extent, and magnitude were each greater during state recreation advisories compared to non-advisory times.

Description:

Cyanobacteria harmful algal blooms (cyanoHABs) negatively affect ecological, human, and animal health. Traditional methods of validating satellite algorithms with data from water samples are often inhibited by the expense of quantifying cyanobacteria indicators in the field and the lack of public data. However, state recreation advisories and other recorded events of cyanoHAB occurrence reported by local authorities can serve as an independent and publicly available dataset for validation. State recreation advisories were defined as a period delimited by a start and end date where a warning was issued due to detections of cyanoHABs over a state's risk threshold. State reported events were defined as any event that was documented with a single date related to cyanoHABs. This study examined the presence-absence agreement between 160 state reported cyanoHAB advisories and 1,343 events and cyanobacteria biomass estimated by a satellite algorithm called the Cyanobacteria Index (CIcyano). The true positive rate of agreement with state recreation advisories was 69% and 60% with state reported events. CIcyano detected a reduction or absence in cyanobacteria after 76% of the recreation advisories ended. CIcyano was used to quantify the magnitude, spatial extent, and temporal frequency of cyanoHABs; each of these three metrics were greater (r > 0.2) during state recreation advisories compared to non-advisory times with effect sizes ranging from small to large. This is the first study to quantitatively evaluate satellite algorithm performance for detecting cyanoHABs with state reported events and advisories and supports informed management decisions with satellite technologies that complement traditional field observations.

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