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Satellites See Red, Blue and Green: Monitoring Harmful Algal Blooms from Space

 

 

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Friday, December 11, 2015

The use of satellites to track harmful algal blooms goes back nearly 30 years, to the fall of 1987, when scientists used NOAA satellite data to track a bloom of Karenia brevis -- the algal species responsible for “Florida red tide”-- off the coast of North Carolina.

S-NPP true-color image of Lake Erie algal bloom on August 16, 2015.
NOAA/NASA’s Joint Polar Satellite Systems’ Suomi NPP satellite captured the above true color image of the Lake Erie algal bloom on August 16, 2015.


“The most severe this century,” that was how scientists at NOAA’s National Centers for Coastal Ocean Science and the Great Lakes Environmental Research Laboratory characterized the immense harmful algal bloom (HAB) in Lake Erie’s western basin this past summer.

Over a 40-day period from late July to the end of August, satellites detected the HAB’s biomass at the highest levels ever recorded. On August 5, dense green scum covered up to 300 square miles of the lake’s western basin—and then it happened a second time on August 15.

HABs can occur in marine, estuarine and fresh waters, and appear to be increasing along the coastlines and in the surface waters of the United States. In marine environments, HABs are estimated to have an average annual cost of $82 million due to impacts on public health, tourism and the seafood industry.

Although HABs occur naturally, human activities that disturb ecosystems seem to be playing a role in their increased occurrence. Excess nutrient and pollution from agricultural runoff, food web alterations, introduced species, water flow modifications, and climate change have all been implicated.

Blooms of harmful algae have become commonplace—every U.S. coastal state has experienced at least one during the past 10 years. Yet, the use of satellites to track HABs goes back nearly 30 years. In the fall of 1987, scientists used data from NOAA’s polar orbiting environmental (POES) satellites to detect ocean thermal features associated with a bloom of Karenia brevis off the coast of North Carolina and provided a means for tracking it. (K. brevis is the algal species responsible for “Florida red tide.”)

According to a group of NOAA scientists who wrote about the episode in an article for Harmful Algae News, the North Carolina bloom “illustrated the need for near real-time satellite data and gave birth to NOAA’s CoastWatch Program.” Today CoastWatch, a program within NOAA’s Satellite and Information Service, provides a variety of satellite-derived environmental data, including products to identify blooms and predict HABs.

Bar graph showing the Lake Erie bloom severity index for 2002 - 2015.
This graph shows the bloom severity index for 2002 - 2015. 2011 is 10, 2015 is 10.5. The index is based on the amount of biomass over the peak 30-day period.

“NOAA CoastWatch uses data from the MODIS instrument on NASA's Aqua satellite and from the VIIRS instrument on Joint Polar Satellite Systems NOAA/NASA Suomi-NPP satellite to generate the chlorophyll concentration and chlorophyll anomaly products,” said Ron Vogel, operations manager for CoastWatch’s East Coast Node. “Chlorophyll concentration, the primary satellite data used in monitoring and forecasting harmful algal blooms, shows high concentration in the presence of algae, or phytoplankton. Chlorophyll anomaly (or “hot spot”) products highlight regions where the chlorophyll is abnormally high on a given day compared to concentrations over a two-month period.”

A Boon to Resource Managers

CoastWatch also sends the chlorophyll concentration data to NOAA’s National Centers for Coastal Ocean Science (NCCOS) for itsHarmful Algal Bloom Operational Forecast System. Launched in January 1999, the forecasts combine the chlorophyll data with wind, water current and other modeled and observed data to identify the location, size and trajectory of harmful blooms so that health officials and resources managers can take protective measures.

The forecast protects public health while saving time and money. For example, before the forecast was available, decision-makers in Florida would have had to close a wide swath of beaches just to be on the safe side, losing tourism dollars. With the forecast in place, local authorities can pinpoint which beaches to close and for how long. This helps minimize the economic impact of beach closures.

VIIRS Chlorophyll-a image of the Gulf of Mexico
Images such as this VIIRS Chlorophyll-a image of the Gulf of Mexico are used to generate Anomaly products used along with other environmental and in situ data to determine the extent of algal bloom formation.

Currently, NCCOS’s operational HAB forecasts focus on the Gulf Coasts of Florida and Texas to monitor and predict blooms of K. brevis. NCCOS’s goal is to provide regionalized HAB forecasts that support all states affected by harmful algal blooms. To make this goal a reality, NOAA has begun demonstration and research projects in five regions—the California Coast, the Chesapeake Bay, the Gulf of Maine, the Washington Coast and, as suggested at the outset of this article, Lake Erie—where HABs are a critical problem to federal, state, and local resource managers.

Postscript: NOAA Announces “Early Warning System” Partnership

Last April, NOAA announced a $3.6 million research effort in partnership with NASA, the U.S. Environmental Protection Agency, and the U.S. Geological Survey to develop an early warning system for toxic and nuisance algal blooms in freshwater systems by using satellites that can gather color data from freshwater bodies during scans of the Earth.

The project also includes a research component to improve understanding of the environmental causes and health impacts of algal bloom across the United States.