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Thousands of years ago, the receding Laurentide Ice Sheet gave North America a gift: five large lakes.

color photo of cladophora on Lake Michigan shoreline
Cladophora washes up on the shore of Lake Michigan at Chicago.

Today, those interconnected Great Lakes, on or near the border of the United States and Canada, represent roughly 20% of the surface freshwater in the world and 90% in the United States.

More than 3,500 plant and animal species inhabit the complex ecoregion of open water, tributaries, wetlands, forests, and dunes. Serious threats to the region’s health range from climate change and invasive species to pollution and development.

Identifying and addressing these threats on a large scale is a daunting task for the limited resources of the eight States and single Province that border the lakes. Field research, monitoring, and restoration measures can be expensive and labor-intensive. But Landsat and other remote sensing tools have helped make some efforts more manageable, especially since a new initiative came about to accelerate progress.

In 2010, the Great Lakes Restoration Initiative (GLRI) began as a nonregulatory program to accelerate efforts to protect and restore the Great Lakes by multiple Federal agencies in collaboration with State, Tribal, and local governments; universities; and nongovernmental organizations. During FY2010-2020, the U.S. Environmental Protection Agency (EPA) received approximately $3.5 billion in federal funds for the GLRI. With those funds, the EPA and other Federal agency partners, including the U.S. Geological Survey (USGS), identify and implement programs and projects that will best advance progress toward achieving long-term Great Lakes goals in partnership with the nonfederal stakeholders. Information about past and current efforts can be found at

If USGS coastal wetland ecologist Dr. Kurt Kowalski had to pick one word to describe GLRI’s effect on Great Lakes restoration, it would be “transformational.”

Kowalski lists several benefits already gained: “a tremendous amount of cleanup of harbors and sediments”; strides made in combating Asian carp, zebra mussels, problematic algae (Cladophora), and invasive plants like Phragmites; and efforts with nutrient runoff and harmful algal blooms.

“It’s hard to overstate the impact and the positive effect that GLRI has had on the ecosystems,” said Kowalski, who works out of the USGS Great Lakes Science Center in Ann Arbor, MI.

Collaboration Is Key to Accomplishing Big Things

The collaboration benefits from a planning process in which projects are developed well in advance by the agencies relevant to certain key areas. The five key areas in GLRI’s current five-year action plan are: toxic substances, invasive species, nearshore health and nonpoint source pollution, habitats and species, and foundations for future restoration.

“The action plan drives it,” said Jon Hortness, the USGS GLRI Program Coordinator. “The agencies find their niche. It’s definitely not a competition. It’s a very collaborative approach.”

Photo of Kurt Kowalski and invasive phragmites
Dr. Kurt Kowalski, a coastal wetland ecologist with the U.S. Geological Survey, stands among towering invasive Phragmites near Lake Erie.

It’s an approach that gets a lot done in the fight against big threats—with “unprecedented results,” the current action plan states, such as preventing more than 1 million pounds of phosphorus used in agriculture from entering the Great Lakes. In the action plan, financial and technical support will continue for farmers who adopt conservation practices and further reduce phosphorus runoff.

The agencies each play their part. “The goal is to support the restoration and really to get work done in the right places,” Hortness said. “From the USGS perspective, we’re not doing any of the actual restoration, but we’re trying to make all of those restoration efforts better. We’re providing the science to inform the restoration.”

The GLRI has funded several thousand projects to date, with costs ranging from thousands to millions of dollars. Here’s a look at a couple of Great Lakes problems that use Landsat as a monitoring tool: the nuisance Cladophora, or benthic green algae, and Kowalski’s work with the invasive plant Phragmites, or common reed.

Mapping Cladophora—stinky, slimy nuisance algae

Dr. Bob Shuchman and Dr. Michael Sayers use remote sensing to help study Great Lakes water quality at the Ann Arbor-based Michigan Tech Research Institute (MTRI), an organization with a history of providing science and engineering expertise to Federal agencies.

GLRI has enhanced the scientists’ research of submerged aquatic vegetation (SAV) such as Cladophora, native green algae that grows on rocky surfaces underwater, especially in areas with high concentrations of nutrients like phosphorus. Cladophora becomes a nuisance when wave action—particularly during storms—causes it to slough off the substrate and float to shore.

“It stinks, it’s slimy,” Shuchman said, and it can harbor botulism bacteria that endanger shorebirds and other wildlife.

Cladophora has even disrupted power by entering a water intake cooling system for a Toronto nuclear power plant on Lake Ontario. If Asian carp invade the Great Lakes, Shuchman predicts the fish will be drawn to areas of Cladophora growth to feed on.

For a GLRI project to map SAV across the Great Lakes Basin, Landsat 5 data were used to differentiate and map dense vegetation, sparse vegetation, or no vegetation on the nearshore bottom of the lower four Great Lakes, where Cladophora is more prevalent, mostly using scenes from 2008-2011. For five specific sites, including Sleeping Bear Dunes National Lakeshore in Michigan, Landsat images were used every five years from 1975-2010.

Landsat, which captures 30-meter pixels of the Earth’s surface every 8-16 days, has amassed an unrivaled archive of imagery stretching back almost 50 years.

“We like to think about Landsat as being, for this particular problem, sort of the sweet spot—the perfect asset,” Sayers said, adding they had considered using a variety of sensors at different resolutions. “We found Landsat was really good at mapping the bulk of biomass for this particular test area we were looking at.”

Interesting Discoveries With Map Update

Color map of change to submerged aquatic vegetation in Michigan
This map of Sleeping Bear Dunes National Seashore on Lake Michigan shows the change in submerged aquatic vegetation (SAV) between 2010 and 2018. Blue shows SAV loss; orange shows SAV gain. Green was SAV in both years; tan was sand in both years. (Map courtesy of Bob Shuchman and Michael Sayers)

Shuchman and Sayers recently used Landsat 8 data to update the SAV map. The number of cloudy days in the region, along with turbidity from rivers and tributaries entering the Great Lakes, can make it a challenge to find clear Landsat images, so data from the European Space Agency (ESA) Copernicus Sentinel-2 satellites helped complement the update with more frequent looks.

Comparing 2010 and 2018 showed where SAV had gains or losses. Historically, nutrients have encouraged Cladophora growth. As efforts to improve water quality reduced nutrients, light traveling through clearer water has become a significant factor in Cladophora growth in the Great Lakes, Sayers and Shuchman said.

A main reason for the mixed-blessing clarity is the invasion of quagga and zebra mussels, which act as filters for the water. Mussel shells also stack up on the lakebed as a hard substrate. “You can imagine that extending through these sandy areas, it’s extending the amount of area that’s suitable for Cladophora to grow,” Sayers said.

In the Great Lakes Basin overall, the latest study showed a “negligible gain” in Cladophora, Sayers said. Most interesting to the researchers were the sites of gains and losses, and the reasons for the changes.

“It wasn’t constant across the lakes—real unique localized things, which the remote sensing is really nice for,” Sayers said.

“The Landsat resolution just did its job,” Shuchman added. “It was literally optimum to give us the tradeoff between synoptic coverage and enough detail to tell the ecological story.”

For example, when time series imagery of Sleeping Bear Dunes National Seashore on the northwestern side of Lower Michigan showed several areas of SAV gains and losses, the pair took a boat out to verify the conflicting results. The losses, they discovered, were caused by degradation and sand cover of mussel shells after the mussels had died. “So it’s actually coming back around that these altered shell bed areas are no longer suitable for Cladophora,” Sayers said.

Meanwhile, recent increasing water levels have encouraged Cladophora to grow closer to some shores.

Dealing With Dense Phragmites Reeds

Kowalski has been studying the invasive Phragmites for more than 15 years. Unlike the smaller and less dense native Phragmites that “plays together with other plants better,” the invasive subspecies towers above and dominates wetlands.

Thriving in disturbed areas, such as Great Lakes coasts with fluctuating water levels and high nutrients, invasive Phragmites stands grow thickly and aggressively. They ruin habitats, views, and beaches and can reduce property values. When they dry out, they can become fire hazards.

Managers have several options to fight invasive Phragmites, including cutting it down, implementing a controlled burn, flooding it, or using herbicide. “Depending on the situation and the resources that people have available, they use combinations of those various tools to try and manage it,” Kowalski said.

map of phragmites online tool
The Phragmites Decision Support Tool shows Phragmites stands in yellow here.

Kowalski is part of the leadership of the Great Lakes Phragmites Collaborative, established by the USGS and the Great Lakes Commission with GLRI funding. Kowalski has played a key role in setting up the collaborative’s Phragmites Adaptive Management Framework, in which land managers volunteer to monitor and provide data about certain Phragmites sites. The data feed into an evolving model that can provide guidance to other managers about what treatment might work best in their situations.

Landsat data fused with radar data—to get around cloud cover issues—helped Kowalski and Phragmites researchers at MTRI, led by Dr. Laura Bourgeau-Chavez, complete the first basin-wide map of large Phragmites stands. That map and a map showing areas suitable for Phragmites growth form the foundation of a Phragmites Decision Support Tool, a resource appreciated by managers throughout the Great Lakes basin.

GLRI has encouraged that large-scale thinking and action—and results. “The vast majority of my research and support for resource managers has been funded by GLRI since 2010,” Kowalski said. “And I’m just one scientist in one agency. There’s tremendous cooperation and collaboration.”

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