Cyanobacterial harmful algal blooms (cyanoHABs) can harm people, fauna, and affect water quality and recreational use of inland waters. Measuring and monitoring cyanobacteria is limited, while chlorophyll-a (chl-a) is a common water quality metric and has been shown to have a relationship with cyanobacteria. The World Health Organization (WHO) has recently updated their previous 1999 cyanoHAB guidance values (GVs) to be more practical by basing the GVs on chl-a concentration. This creates an opportunity for widespread monitoring of cyanoHABs based on chl-a proxy measures, with satellite remote sensing (SRS) being a potentially powerful tool. This study assessed the comparability of SRS of chl-a for cyanotoxin public health advisories. We used Sentinel-2 and 3 to map chl-a and cyanobacteria, respectively, and classified the values according to WHO GVs. We then compared them to the existing GVs set by the Department of Water Resources (DWR) at San Luis Reservoir, the largest off-stream reservoir in the United States and a key piece of infrastructure in California’s water system. We found mismatches between the SRS-derived WHO 2021 chl-a GV and DWR GVs. However, SRS-based chl-a GVs never missed a bloom detected by the DWR, and warning levels were typically no more than a level off. SRS can help fill temporal data gaps and provide greater spatial information not available from using only in-situ measurements. Using SRS-based chl-a GVs as an early indicator for possible exposure advisories and as a trigger for in-situ sampling may be effective to improve public health warnings.

Primary Presenter: Brittany Lopez Barreto, University of California, Merced (blopezbarreto@ucmerced.edu)

Authors:

Brittany Lopez Barreto, University of California, Merced  (blopezbarreto@ucmerced.edu)

Erin Hestir, University of California, Merced  (ehestir@ucmerced.edu)

Christine Lee, NASA Jet Propulsion Laboratory  (christine.m.lee@jpl.nasa.gov)

Marc Beutel, University of California, Merced  (mbeutel@ucmerced.edu)