For the 5th consecutive year, the National Centers for Coastal Ocean Science (NCCOS) will issue weekly forecasts for the extent, intensity and likely impacts of harmful algal blooms (HABs) in Lake Erie. These annual blooms of toxic cyanobacteria, or blue green algae, start in the summer as water temperatures increase. Typically the blooms reach maximum size sometime in August or September (Figure 1).
The detection is done using high temporal resolution satellite imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensor. The forecasts are issued on a weekly basis from the first week of June to the last week of October; generally they are issued a day after a clear satellite image that does not contain cloudy conditions. The satellite detected biomass is imported into a particle tracking software system developed by our colleagues in the Office of Response and Restoration, and the bloom movement is simulated using a two dimensional hydrodynamic model provided by the Great Lakes Environmental Laboratory. The image generally takes a day to be acquired and processed. The likely bloom trajectory is first written out into the likely current position, called a “nowcast”. The nowcast is then simulated with modeled current data, creating a forecast, predicting where the bloom will be up to 3 days past the current observed conditions. The forecasts consider the effects of water temperature as well as wind stress. Elevated wind stress will have a tendency to mix the cyanobacteria biomass throughout the water column, which can cause an underestimation from the satellite observation, as the satellite can only record what is within the top meter of the water column. Additionally, increased winds can cause the bloom to break up and weaken. Water temperature is another component. The blooms generally do better under warmer water temperatures and, tend to dissipate under cooler temperatures, so water temperature is also monitored. An example of one of last year’s forecasts is seen in figure 2.
The HAB bulletin was started in 2008 and only distributed to a select group of users. In 2009, the forecast system became demonstrational, and was posted on the internet (archived http://www2.nccos.noaa.gov/coast/lakeerie/bulletin/), as well as emailed to a list of subscribers. The subscriber list includes public health managers, water supply managers, beach managers, natural resource managers, and researchers. The number of forecasts and subscribers is seen in figure 3, and has generally trended upwards each year.
NCCOS Blogger Biography:
Tim Wynne is an physical scientist at NOAA’s NCCOS, CCMA, COAST Branch. He has been conducting remote sensing HABs research for over ten years. He received a B.S. in marine science from the Richard Stockton College of New Jersey and an M.S. in oceanography from Old Dominion University. He is currently pursuing a Ph.D. at the University of Maryland.