Scientists don’t need to be out on the water collecting jars of algae to help measure a bloom – they can do it from space, too.
A team of scientists was able to use historical data from NASA ocean color satellites to measure the extent of Great Lakes algal blooms back to 1997, even before satellites were actively collecting the data. Michigan Tech Research Institute Co-Director Robert Shuchman said they wanted to answer the question on whether or not harmful algal blooms, or HABs, were getting worse year-to-year, focusing primarily on three areas: the western basin of Lake Erie, Green Bay in Lake Michigan and Saginaw Bay in Lake Huron. Thanks to a grant through the Great Lakes Restoration Initiative, they were able to begin the project about five years ago.
Using the data as a “time machine,” Shuchman said they were able to figure out the average extent of the blooms each year in those three basins. They found that all three locations seemed to behave independently of each other, even though they have similar weather patterns and are relatively near each other. While the extent of algal blooms on Lake Erie has been generally increasing, especially since 2006, Saginaw Bay has been fluctuating year-to-year. Green Bay blooms also fluctuate based on runoff and air temperature in the basin.
Michael Sayers, the researcher in charge of the study, said the lack of perennial HAB trends in those two bays compared to Lake Erie is possibly due to land use and geography. The worst of Lake Erie’s algal blooms is due to agricultural nutrients getting into the Maumee River during the spring, which in turn deposits them into Lake Erie.
Sayers said around 70-80 percent of the Maumee watershed is agricultural. In contrast, the Saginaw River and Fox River watersheds are closer to 40 percent agricultural. They also seem to react differently to weather factors like temperature, precipitation and seasonal climate – leading Sayers to believe that these blooms are “locally controlled phenomena.” The US Department of Agriculture’s Natural Resource Conservation Service has held community outreach efforts and directed money to farmers in the Saginaw River system to work with local agricultural producers to reduce sediment getting into the Saginaw Bay, Sayers said, so local factors could be playing a role beyond the weather, such as Michigan’s phosphorus-reduction legislation.
By correlating the satellite data with “resuspension events” involving winds and waves, the researchers found that resuspension of phosphorus into the water column from bottom sediments also does not seem to be the same issue in Green Bay and Saginaw Bay as it is in western Lake Erie. Sayers said looking in the areas where the blooms pop up repeatedly, there were few events that could have caused resuspension. He hypothesized that Green Bay’s narrow and long morphology may help protect the waterway from winds strong enough to cause resuspension, where phosphorus that has settled into the lake floor is churned back up into the water, providing new fuel for algal blooms.
Using satellites allows researchers to see a long-term analysis of the lakes and the blooms, adding some extra information on the cause and effects of HABs. There are some limitations, though. Shuchman said the land adjacent to the narrow Green Bay has a tendency to form cloud cover early in the day that doesn’t always clear up by the time the satellite moves overhead, and extended periods of cloud cover over parts of the lakes effectively blind the satellites from seeing surface conditions. Shuchman said aircraft now fly over Lake Erie once a week during the July-September HAB season, which helps collect data when it’s too cloudy for satellites. In the next few years, he hopes to add lower-flying drones to monitor the lakes on particularly cloudy days.
This information can be helpful from a public health standpoint as well. The toxicity of harmful algal blooms can make humans sick if ingested and cause rashes if touched, while it can outright kill dogs and other animals. Shuchman said the data is already used by water treatment facilities to protect their intake systems, and natural resources departments in each state for public safety regarding fishing and other uses of the water.
Sayers said satellites currently in use are primarily sensitive to plant-like green algae, but going forward researchers should be able to collect what’s known as hyperspectral data that can delve deep into subtle color differences. This would allow them to identify specific phytoplankton species and types, including some blue-green colored cyanobacterial algae like those found in toxic HABs. Sayer said the information would be helpful for resource managers and stakeholders in these areas, to find out what kind of toxicity they can expect from a bloom for planning water treatment and usage advisories. Green algae and blue-green algae species are not closely related, but both use the “algae” name based on being aquatic and being able to manufacture their own food using sunlight and nutrients in the water.
“Field measurements have been going on for a long time, but HABs are a complex issue, and remote sensing has added some information on cause-and-effect of HABs,” Sayers said.
Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.