Using satellite imagery and national surveys to identify lakes at risk for toxic cyanobacteria blooms in the US

Harmful algal blooms caused by cyanobacteria are a threat to global water resources and human health. Satellite remote sensing has vastly expanded spatial and temporal data on lake cyanobacteria, yet there is still acute need for tools that identify which waterbodies are at-risk for toxic cyanobacterial blooms. Algal toxins cannot be directly detected through imagery but monitoring toxins associated with cyanobacterial blooms is critical for assessing risk to the environment, animals, and people. The objective of this study is to address this need by developing an approach relating satellite imagery on cyanobacteria with field surveys to model the risk of toxic blooms among lakes. The Medium Resolution Imaging Spectrometer (MERIS) and United States (US) National Lakes Assessments are leveraged to model the probability among lakes of exceeding lower and higher demonstration thresholds for microcystin toxin, cyanobacteria, and chlorophyll a. By leveraging the large spatial variation among lakes using two national-scale data sources, rather than focusing on temporal variability, this approach avoids many of the previous challenges in relating satellite imagery to cyanotoxins. For every satellite-derived lake-level Cyanobacteria Index (CI_cyano) increase of 0.01 CI_cyano/km2, the odds of exceeding six bloom thresholds increased by 23–54%. When the models were applied to the 2,192 satellite monitored lakes in the US, the number of lakes identified with ≥75% probability of exceeding the thresholds included as many as 335 lakes for the lower thresholds and 70 lakes for the higher thresholds, respectively. For microcystin, the models identified 162 and 70 lakes with ≥75% probability of exceeding the lower (0.2 µg/L) and higher (1.0 µg/L) thresholds, respectively. This approach represents a critical advancement in using satellite imagery and field data to identify lakes at risk for developing toxic cyanobacteria blooms. Such models can help translate satellite data to aid water quality monitoring and management.

Impact/Purpose

Harmful cyanobacterial blooms can produce toxins which impair freshwater ecosystems used for drinking water, recreation, and habitat for aquatic biota. With increased awareness and reporting of cyanobacteria blooms, water managers need information about how to prioritize monitoring locations in surface waters that may be affected. This presentation highlights an analysis that combines data from the remote sensing Cyanobacteria Assessment Network and the National Lakes Assessments field surveys to determine the risk of toxic blooms in large lakes across the US. The audience for this presentation is the Pacific Northwest Section of the American Water Works Association. The Association is convening a Cascade to Coast Short School to support the continuing education of water and wastewater operators in the pacific northwest region of the country. Their feedback on this work will improve understanding of stakeholder needs regarding cyanobacteria blooms.

Citation

Handler, A., J. Compton, Ryan A Hill, S. Leibowitz, B. Schaeffer, AND M. Dumelle. Using satellite imagery and national surveys to identify lakes at risk for toxic cyanobacteria blooms in the US. Pacific Northwest Section of the American Water Works Association Cascade to Coast Short School, Albany, OR, February 27 - March 02, 2023.