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Satellite Imagery Used to Measure Algal Bloom Frequency—Steps Toward Understanding Exposure Risk

Map of the frequency of cyanoHAB occurrence above the WHO high threshold - Florida 2008 through 2011
Map of the frequency of observed cyanoHAB occurrence above the World Health Organization (WHO) high threshold for risk of 100,000 cells per milliliter (cells mL−1) in central Florida lakes from 2008 through 2011. A value of 1 indicates that the pixel was observed to have cyanoHABs above the WHO threshold in all observations, and a value of 0 indicates that the pixel had no cyanoHABs above the threshold. Modified from figure 7, Clark and others, 2017.

Study explores the utility and limitations of currently available remotely sensed satellite data for identifying the frequency of algal blooms in the Nation's lakes and reservoirs. This information provides a first step toward the goal of understanding exposure risk to protect the health of humans, pets, livestock, and wildlife.

Our Nation's lakes and reservoirs provide drinking water, habitat for wildlife, and recreational opportunities. Harmful algal blooms (HABs) can result in the loss of recreational opportunities and income, loss of aquatic habitat and important fisheries, and present health risks associated with exposure to the toxins these blooms can produce. One of the most common forms of HABs in inland lakes and reservoirs, cyanobacteria harmful algal blooms (CyanoHABs), can produce toxins that pose a range of health risks to humans, pets, livestock, and wildlife.

Although toxins cannot be directly measured from space, the pigments associated with algal blooms can be measured using remotely sensed data from satellites. Previous research indicates strategies to link toxin concentrations with pigments sensed remotely. There are questions as to the efficacy of the currently (2017) available remotely sensed data to identify algal blooms in small waterbodies used for recreation and drinking water, and the ability to use the data to understand trends in CyanoHABs over time.

Scientists developed an approach to assess the frequency of CyanoHABs over time at two test regions. This research was part of the Cyanobacteria Assessment Network (CyAN), which is a multiagency project among the National Aeronautics and Space Administration (NASA), National Oceanic and Atmospheric Administration (NOAA), U.S. Geological Survey (USGS), and the U.S. Environmental Protection Agency (EPA) to develop an early warning indicator system using historical and current satellite data to detect algal blooms in U.S. freshwater systems.

Scientists explored the utility and limitations of current satellite-based technology to determine CyanoHAB occurrence. Four methods of calculating CyanoHAB frequency above defined thresholds were developed for recreational and drinking water sources in Florida and Ohio from 2008 through 2011. Scientists determined that CyanoHAB occurrence patterns could be reliably estimated at these two test locations, indicating that the approach may be more broadly applicable throughout the Nation, particularly as satellites of sufficient resolution and sensing capabilities become available.

Limitations for successful implementation of the approach include satellite resolution and sensing capabilities. Currently available satellites with the highest resolution, such as Landsat, can capture 62 percent of lakes greater than 1 hectare (2.47 acres) and 95 percent of the lakes with public drinking water intake locations. Unfortunately, these satellites make less frequent flyovers and are not equipped with sensors capable of distinguishing CyanoHABs from other types of HABs. Lower resolution satellites capture less than 1 percent of waterbodies and only 33 percent of drinking water intakes but make flyovers that are more frequent and can identify CyanoHABs.

This study provides consistent and transferrable methods to characterize CyanoHAB frequency using remotely sensed data. The utility and limitations of the currently available satellite data for understanding CyanoHAB frequency is highlighted, including the importance of satellite resolution and sensing capability for measuring CyanoHABs on small inland lakes. This information can help identify and prioritize the resolution, observation frequency, and sensing capabilities needed for future imagers that are better equipped for algal bloom detection.

This study is part of a larger effort of the USGS Environmental Health Mission Area to provide information that will help resource managers understand how to effectively minimize potential risks to the health of humans and other organisms exposed to cyantotoxins and other biogenic toxins through recreation, drinking water, and other exposure routes.

This study was supported by the NASA Ocean Biology and Biogeochemistry Program/Applied Science Program (proposal NASA 14-SMDUNSOL14- 0001), the EPA, NOAA, and the USGS Toxic Substances Hydrology Program.

References

Clark, J.M., Schaeffer, B.A., Darling, J.A., Urquhart, E.A., Johnston, J.M., Ignatius, A.R., Myer, M.H., Loftin, K.A., Werdell, P.J., and Stumpf, R.P., 2017, Satellite monitoring of cyanobacterial harmful algal bloom frequency in recreational waters and drinking water sources: Ecological Indicators, v. 80, p. 84-95, doi:10.1016/j.ecolind.2017.04.046.

Stumpf, R.P., Davis, T.W., Wynne, T.T., Graham, J.L., Loftin, K.A., Johengen, T.H., Gossiaux, D., Palladino, D., and Burtner, A., 2016, Challenges for mapping cyanotoxin patterns from remote sensing of cyanobacteria: Harmful Algae, v. 54, p. 160-173, doi:10.1016/j.hal.2016.01.005.

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