POSTER Session 2

TEMPORAL CYANOBACTERIA TRENDS IN A HYPEREUTROPHIC LAKE USING REMOTE SENSING: FROM MULTISPECTRAL TO HYPERSPECTRAL

Cyanobacteria Harmful Algal Blooms (CHABs) and their associated toxicity are a significant concern for inland waters. Due to the extensive spatial coverage and frequent data availability of satellite-based sensors, multispectral remote sensing tools have demonstrated utility for monitoring, understanding, and managing these blooms in large lakes. The next frontier for remote sensing of CHABs in inland waters is hyperspectral data. Recent and upcoming hyperspectral satellite missions will have an enormous impact on our ability to measure and quantify cyanobacteria. This study compares the utility of multispectral and hyperspectral remote sensing tools for monitoring cyanobacteria blooms. We evaluated the temporal trends of CHABs in Clear Lake, CA, a hypereutrophic lake with diverse cyanobacteria populations during 38 sampling events over a 5-year water quality monitoring period (2019-2023). We validated the Sentinel-3 OLCI Cyanobacteria Index algorithm using in situ cyanobacteria measurements. This remote sensing data complemented our evaluation of cyanobacteria trends in Clear Lake. We then demonstrate the advantages of using hyperspectral remote sensing measurements for monitoring cyanobacteria blooms using in situ spectroradiometer measurements collected during 12 field events in 2021-2022 across all seasons. This hyperspectral dataset also includes three full-lake data acquisitions by the DESIS sensor during the Summer and Fall 2022, when we encountered the highest concentration cyanobacteria blooms during our 5-year sampling period. The results of this study will support the development of future tools utilizing satellite-based imaging spectroscopy data to identify the cyanobacteria genera present in a bloom, and thus the potential for cyanotoxin production.

*Samantha L. Sharp, University of California, Davis, USA, https://orcid.org/0000-0002-9297-2004

Alicia Cortés, University of California, Davis, USA, https://orcid.org/0000-0002-4873-4164

Alexander L. Forrest, University of California, Davis, USA, https://orcid.org/0000-0002-7853-9765

S. Geoffrey Schladow, University of California, Davis, https://orcid.org/0000-0003-4205-1001

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